Experimental Design and Scientific Method Practice Questions — ACT — Page 4

A student proposes the following hypothesis regarding the thermal stability of Group 2 metal carbonates:

*Hypothesis*: The decomposition temperature of a Group 2 metal carbonate is directly proportional to the charge density of its metal cation. Because charge density decreases as ionic radius increases, metal carbonates with larger metal cations will decompose at lower temperatures.

A chemist conducts an experiment to test this hypothesis by measuring the decomposition temperature ( $T_d$ , the temperature at which the carbonate decomposes into a metal oxide and carbon dioxide) of four Group 2 metal carbonates. The results are shown in Table 1.

### Table 1

Metal Carbonate	Metal Cation	Cation Ionic Radius ( $\text{pm}$ )	Decomposition Temperature ( $^\circ\text{C}$ )
$\text{MgCO}_3$	$\text{Mg}^{2+}$	72	350
$\text{CaCO}_3$	$\text{Ca}^{2+}$	100	825
$\text{SrCO}_3$	$\text{Sr}^{2+}$	118	1,100
$\text{BaCO}_3$	$\text{Ba}^{2+}$	135	1,360

Based on Table 1, is the student's hypothesis supported by the experimental results, and how should the hypothesis be modified?

Yes; the data show that as the ionic radius of the metal cation increases, the decomposition temperature also increases.

No; the hypothesis should be modified to state that as the ionic radius of the metal cation increases, the decomposition temperature increases.

No; the hypothesis should be modified to state that the decomposition temperature of a Group 2 metal carbonate is independent of the metal cation's ionic radius.

Yes; the data show that

\text{MgCO}_3

, which contains the metal cation with the highest charge density, decomposes at the lowest temperature.

Show answer & explanation

Answer: No; the hypothesis should be modified to state that as the ionic radius of the metal cation increases, the decomposition temperature increases.

Answer

The student's hypothesis is not supported because the experimental data show that as the ionic radius of the metal cation increases, the decomposition temperature increases. Therefore, the hypothesis should be modified to state that as the ionic radius of the metal cation increases, the decomposition temperature increases.

The experimental results show that as the ionic radius increases, the decomposition temperature increases. This trend is the opposite of the student's prediction that larger cations would decompose at lower temperatures. Thus, the hypothesis is not supported and must be modified to state that as the ionic radius of the metal cation increases, the decomposition temperature increases.

Step-by-Step Solution

1

Determine the prediction made by the student's hypothesis.

The student predicted that since charge density decreases as ionic radius increases, larger metal cations would lead to lower decomposition temperatures (an inverse relationship between ionic radius and decomposition temperature).

To evaluate a hypothesis, we must first clearly define the relationship it predicts.

2

Analyze the experimental data in Table 1 to identify the actual trend.

As the ionic radius of the cation increases from

72\text{ pm}

(

\text{Mg}^{2+}

) to

135\text{ pm}

(

\text{Ba}^{2+}

), the decomposition temperature increases from

350\ ^\circ\text{C}

to

1,360\ ^\circ\text{C}

(a direct relationship).

This establishes the empirical relationship demonstrated by the experiment.

3

Compare the predicted trend with the observed trend.

The observed direct relationship is the opposite of the predicted inverse relationship, meaning the hypothesis is not supported.

Comparing predictions with actual data determines whether the hypothesis is supported or refuted.

4

Formulate the correct modification to the hypothesis.

The hypothesis should be modified to state that as the ionic radius of the metal cation increases, the decomposition temperature increases.

Modifying a refuted hypothesis requires aligning it with the experimental evidence.

Key Concept

Evaluating and modifying a hypothesis based on empirical data trends

Question 62Question →

Suppose a scientist wants to modify an electroplating procedure to isolate the specific effect of temperature on the deposition rate of copper and determine the activation energy of the reaction. The scientist must ensure that concentration depletion and current fluctuations do not confound the results. Arrange the following steps in the correct chronological order to design and execute this modified follow-up experiment.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence begins with preparing the high-volume electrolyte bath to maintain constant concentration. Next, preliminary trials are run to determine the optimal constant current. Once the current is established, the temperature-controlled trials are executed. After the trials, the deposited mass is measured to calculate rates. Finally, these rates are plotted against the reciprocal of absolute temperature to calculate the activation energy.

The correct sequence begins with preparing the high-volume electrolyte bath to ensure concentration remains constant. Next, preliminary trials must be run to determine the optimal current. Once the current is established, the temperature-controlled trials are executed. After completing the trials, the mass of deposited copper is measured to calculate rates. Finally, these rates are plotted to calculate activation energy.

Step-by-Step Solution

1

Prepare the constant concentration electrolyte bath.

Maintains a stable chemical environment.

This must be done first so that all subsequent trials, including preliminary calibration, use the same electrolyte concentration.

2

Run preliminary trials to select the operating current.

Determines the optimal constant current value.

A constant current must be selected prior to running the main experimental trials to properly control this variable.

3

Execute the temperature-controlled trials.

Generates copper deposition at different temperatures.

This step uses the selected current and prepared bath to collect raw data across the independent temperature variable.

4

Measure mass and calculate deposition rates.

Obtains the rate of deposition for each temperature.

The rate data is the dependent variable required for the final activation energy calculation.

5

Construct an Arrhenius plot.

Determines the activation energy.

This final analytical step uses the rates calculated from the trials to perform the mathematical analysis.

Key Concept

Isolating independent variables and controlling confounding factors in a multi-step sequence for follow-up experimental design.

Estimated Time:3m 0s

Question 63Question →

A student wants to investigate how the volume of water affects the time it takes for the water to boil. In Trial 1, the student heats $100\text{ mL}$ of water in a glass beaker on a hot plate set to High (Level $10$ ). In Trial 2, the student heats $200\text{ mL}$ of water in an identical glass beaker on a different hot plate set to Medium (Level $5$ ). Which of the following is an uncontrolled variable in this experiment that prevents the student from drawing a valid conclusion?

The boiling time of the water

The volume of water used in each trial

The heat setting of the hot plates

The material of the beakers

Show answer & explanation

Answer: The heat setting of the hot plates

Answer

The heat setting of the hot plates

To determine how water volume affects boiling time, all other variables, such as the heat setting of the hot plates, must be kept constant. Because the hot plates were set to different levels (High in Trial 1 and Medium in Trial 2), the heat setting is an uncontrolled variable that confounds the results.

Step-by-Step Solution

1

Identify the independent variable (what is intentionally changed to test its effect) and the dependent variable (what is measured).

The independent variable is the volume of water (

100\text{ mL}

vs.

200\text{ mL}

). The dependent variable is the boiling time.

This establishes the core relationship the student intends to study.

2

Examine the experimental procedure for any variables other than the independent variable that changed between trials.

The heat setting changed between trials (Level

10

in Trial 1, Level

5

in Trial 2).

Any variable that changes alongside the independent variable acts as a confounding variable, making it impossible to determine which factor caused the observed change in the dependent variable.

3

Identify the variable that was kept constant to confirm it is not confounding.

The beaker material was kept constant (both were identical glass beakers).

Controlled variables do not introduce experimental error or confound the results.

Key Concept

Identifying Sources of Error and Confounding Variables

Estimated Time:45s

Question 64Question →

To investigate how reactant surface area affects the rate of a chemical reaction, students performed three trials. In each trial, $5.0\text{ g}$ of calcium carbonate ( $CaCO_3$ ) was added to $100\text{ mL}$ of $1.0\text{ M}$ hydrochloric acid ( $HCl$ ) at an initial temperature of $20.0^\circ\text{C}$ in an uninsulated beaker. The reaction is represented by the following equation:

CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + CO_2(g) + H_2O(l) + \Delta H

The students recorded the particle size of the $CaCO_3$ , the time required for the reaction to go to completion, and the maximum temperature reached during each trial. The results are shown in the table below:

Trial	$CaCO_3$ Particle Size	Time to Completion (s)	Maximum Temperature Reached ( $^\circ\text{C}$ )
$1$	Large chunks	$240$	$21.5$
$2$	Small chips	$120$	$26.2$
$3$	Fine powder	$30$	$38.8$

Which of the following statements best explains how the maximum temperature reached acts as a confounding variable that prevents the students from drawing a valid conclusion about the effect of particle size on the reaction rate?

The maximum temperature reached is the independent variable, which the students should have controlled by varying the initial mass of the calcium carbonate added to each beaker.

The temperature differences indicate that Trial 1 was conducted in a colder room than Trial 3, showing a failure to keep the ambient experimental environment constant.

The unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size.

The maximum temperature is a controlled variable because the reactants in all three trials began at the same initial temperature of 20.0°C.

Show answer & explanation

Answer: The unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size.

Answer

The correct answer explains that the unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size.

The correct answer explains that the unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size. Since temperature is known to affect reaction rate, the fact that the temperature rose much higher in the fine powder trial than in the large chunks trial means that both temperature and surface area changed simultaneously, confounding the results.

Step-by-Step Solution

1

Identify the independent, dependent, and controlled variables in the setup.

The independent variable is the particle size of calcium carbonate, and the dependent variable is the time to completion. The controlled variables include the mass of calcium carbonate, the volume and concentration of hydrochloric acid, and the initial temperature.

Establishing the variable roles is necessary to detect any extraneous variables that are not properly controlled.

2

Analyze the maximum temperature data across the trials.

The maximum temperature rose from

21.5^\circ\text{C}

in Trial 1 (slowest) to

38.8^\circ\text{C}

in Trial 3 (fastest).

This temperature difference shows that a variable influencing reaction rate (temperature) was not constant across trials during the reaction.

3

Determine how this temperature variation affects the interpretation of the results.

Higher temperatures increase the kinetic energy of reactants, which accelerates the reaction. Therefore, the faster rate in Trial 3 is caused by both the smaller particle size and the higher temperature.

This shows that temperature acts as a confounding variable, making it impossible to isolate the effect of particle size alone.

Key Concept

A confounding variable is an uncontrolled factor that varies systematically with the independent variable, making it impossible to isolate the true cause of the observed changes in the dependent variable.

Estimated Time:2m 0s

Question 65Question →

In scientific investigations, identifying potential sources of error and confounding variables is critical to ensuring the validity of experimental results. Match each experimental scenario to the primary uncontrolled confounding variable that threatens the validity of its results.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The plant growth experiment matches with differences in sunlight exposure; the salt water boiling experiment matches with variations in water purity; and the ice melting experiment matches with differences in ambient temperature.

Each correct pairing links an experimental setup that fails to keep a background condition constant with the specific environmental or chemical factor that was allowed to vary.

Step-by-Step Solution

1

Analyze the plant growth experiment to identify the variables.

The independent variable is fertilizer amount, but the groups also differ in location (sunny window vs. dark closet), which introduces sunlight as an uncontrolled variable.

To ensure a fair test, all factors other than the fertilizer amount must be kept constant.

2

Analyze the salt water boiling point experiment to identify the variables.

The trials use different types of water (tap vs. distilled), introducing chemical impurities as a confounding variable.

Impurities in solvent can alter boiling point, confounding the effect of the added salt.

3

Analyze the ice melting experiment to identify the variables.

The trials are performed in different locations with different ambient temperatures (indoor air-conditioning vs. outdoors), introducing temperature as an uncontrolled variable.

Ambient temperature directly affects the rate of heat transfer and ice melting.

Key Concept

Identifying Sources of Error and Confounding Variables

Question 66Question →

A student conducted an experiment to investigate the effect of light wavelength on the rate of photosynthesis in *Elodea* plants. The student formulated the following hypothesis:

*Hypothesis:* The rate of photosynthesis, as measured by the volume of oxygen ( $O_2$ ) gas produced per hour, increases continuously as the wavelength of light increases from $400\text{ nm}$ to $700\text{ nm}$ .

The student exposed identical *Elodea* plants to different wavelengths of light for 1 hour each, keeping all other environmental variables constant. The results are shown in the table below:

Wavelength	Volume of $O_2$ produced
$400\text{ nm}$	$1.2\text{ mL}$
$450\text{ nm}$	$4.5\text{ mL}$
$550\text{ nm}$	$0.3\text{ mL}$
$650\text{ nm}$	$5.8\text{ mL}$
$700\text{ nm}$	$1.0\text{ mL}$

Based on the results of the experiment, does the data support the student's hypothesis, and how should the hypothesis be modified?

Yes; the data show that the overall rate of photosynthesis increases continuously from

400\text{ nm}

to

700\text{ nm}

.

No; the rate of photosynthesis does not increase continuously, so the hypothesis should be modified to state that photosynthesis peaks under blue (

450\text{ nm}

) and red (

650\text{ nm}

) light.

Yes; the rate of photosynthesis is highest at

650\text{ nm}

, which is greater than the rate at any lower wavelength tested.

No; the rate of photosynthesis decreases continuously, so the hypothesis should be modified to state that the rate is inversely proportional to wavelength.

Show answer & explanation

Answer: No; the rate of photosynthesis does not increase continuously, so the hypothesis should be modified to state that photosynthesis peaks under blue ( $450\text{ nm}$ ) and red ( $650\text{ nm}$ ) light.

Answer

No; the rate of photosynthesis does not increase continuously, so the hypothesis should be modified to state that photosynthesis peaks under blue (

450\text{ nm}

) and red (

650\text{ nm}

) light.

The correct answer is correct because the experimental results show that oxygen production does not increase continuously. Instead, it rises and falls, reaching local maxima at

450\text{ nm}

and

650\text{ nm}

, and a minimum at

550\text{ nm}

. Therefore, the hypothesis is unsupported and must be modified to state that photosynthesis is most efficient (peaks) at specific wavelengths corresponding to blue and red light.

Step-by-Step Solution

1

Analyze the student's hypothesis.

The hypothesis predicts a continuous, monotonic increase in oxygen production as wavelength increases from

400\text{ nm}

to

700\text{ nm}

.

Understanding the prediction is necessary to evaluate it against the experimental data.

2

Examine the trend in the data table.

The volume of oxygen increases from

1.2\text{ mL}

(at

400\text{ nm}

) to

4.5\text{ mL}

(at

450\text{ nm}

), drops to

0.3\text{ mL}

(at

550\text{ nm}

), increases to

5.8\text{ mL}

(at

650\text{ nm}

), and drops again to

1.0\text{ mL}

(at

700\text{ nm}

).

This determines whether the actual rate of photosynthesis increases continuously.

3

Compare the data to the hypothesis and determine the appropriate modification.

Because the trend shows peaks at

450\text{ nm}

and

650\text{ nm}

rather than a continuous increase, the hypothesis is not supported and should be modified to describe these dual peaks.

Formulating a modified hypothesis must accurately represent the observed experimental results.

Key Concept

Formulating and Modifying Hypotheses

Estimated Time:1m 30s

Question 67Question →

A student conducted an experiment to measure the distance a $50\text{ g}$ toy car traveled along a flat floor after rolling down a $1\text{ m}$ wooden ramp set at an angle of $30^\circ$ . The student performed 3 trials using the same car and ramp. Suppose the student wants to design a follow-up experiment to determine how the mass of the car affects the distance it travels. Which of the following modifications to the procedure should the student make to test this relationship?

Test the original

50\text{ g}

toy car on ramps of different materials and different lengths.

Test toy cars of different masses while increasing the ramp angle for each heavier car.

Test toy cars of different masses while keeping the ramp angle, ramp length, and ramp material the same.

Measure the time it takes the original

50\text{ g}

toy car to reach the bottom of the ramp at various release heights.

Show answer & explanation

Answer: Test toy cars of different masses while keeping the ramp angle, ramp length, and ramp material the same.

Answer

Test toy cars of different masses while keeping the ramp angle, ramp length, and ramp material the same.

The correct answer proposes varying only the mass of the toy car while keeping all other parameters—such as ramp angle, length, and material—constant. This isolates the car's mass as the single independent variable, which is necessary to determine its direct effect on the distance traveled.

Step-by-Step Solution

1

Identify the independent variable that needs to be tested in the follow-up experiment.

The independent variable is the mass of the toy car.

The student wants to determine the specific effect of the car's mass on the distance it travels.

2

Identify the controlled variables that must remain constant.

The ramp angle (

30^\circ

), ramp length (

1\text{ m}

), and ramp material (wooden) must remain unchanged across trials.

To ensure a fair test, all variables except the one being tested must be controlled.

3

Evaluate the choices to find the one that alters only the mass of the car while keeping the ramp conditions constant.

Testing cars of different masses with the same ramp setup is the correct design.

This isolates the mass of the car as the single independent variable affecting the dependent variable (distance traveled).

Key Concept

To isolate the effect of a new independent variable in a follow-up experiment, only that variable should be changed, while all other variables from the original design must be controlled.

Question 68Question →

A student group is designing various laboratory investigations. During their planning phase, they identify potential sources of error and confounding variables in their experimental setups. Match each described experimental procedure with the primary source of error or confounding variable that threatens its validity.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Testing yeast respiration temperature effects matches with light exposure confounding; comparing plant transpiration in clay vs. plastic pots matches with container permeability differences; determining pH effects on enzymes using different buffers matches with chemical interference from buffer salts; investigating wind speed effects at different times of day matches with fluctuating ambient humidity.

Each experimental procedure is correctly matched to its confounding variable: testing yeast at different temperatures under different light conditions introduces light as an uncontrolled variable; using different pot materials (clay vs. plastic) introduces container permeability as a confounder; using different buffer compounds introduces chemical interference; and conducting evaporation trials at different times of day introduces fluctuating relative humidity as an uncontrolled factor.

Step-by-Step Solution

1

Analyze the yeast respiration procedure.

The yeast respiration experiment varies both temperature (

30^\circ\text{C}

vs.

20^\circ\text{C}

) and light exposure (dark incubator vs. lit window). This introduces light as a confounding factor.

Identifying that multiple independent variables are changing at once highlights the source of error.

2

Analyze the plant transpiration comparison.

The plant transpiration experiment uses porous clay pots for one species and non-porous plastic pots for another. Clay pots allow water evaporation through their walls, introducing container permeability as an uncontrolled variable.

Isolating structural differences in experimental containers reveals the confounding factor.

3

Analyze the enzyme pH activity experiment.

Using different buffer formulations to vary pH introduces different chemical salts. If these salts bind to the enzyme, the observed activity changes may stem from chemical interference rather than pH.

Recognizing that changing buffer types introduces new chemical species explains the confounding effect.

4

Analyze the soil evaporation and wind speed experiment.

Running wind speed trials at different times of day (morning vs. night) in an environment with fluctuating relative humidity introduces humidity as an uncontrolled variable.

Identifying temporal differences in testing conditions reveals the environmental confounding variable.

Key Concept

Identifying uncontrolled variables and confounding factors that prevent researchers from drawing valid conclusions about the relationship between the independent and dependent variables.

Question 69Question →

An investigator designed an experiment to determine how pH affects the rate of starch hydrolysis by the enzyme amylase. The investigator prepared four test tubes, each containing an identical concentration of starch and amylase at a specific pH. To establish and maintain each pH level, the investigator used different buffer systems, as summarized in the table below:

Tube	pH	Buffer System Components	Rate of Starch Hydrolysis ( $\text{mg/min}$ )
1	$4.0$	Citric acid / Sodium citrate	$0.2$
2	$6.0$	Phosphate buffer / Sodium chloride	$1.8$
3	$8.0$	Tris-HCl / Potassium chloride	$1.2$
4	$10.0$	Carbonate / Bicarbonate	$0.1$

Given that amylase activity is stimulated by the presence of chloride ( $Cl^-$ ) ions, which of the following statements best identifies the confounding variable in this experiment and its potential impact on the results?

The presence of chloride ions in the buffers for Tube 2 and Tube 3, which may artificially elevate the measured hydrolysis rates at pH 6.0 and pH 8.0.

The variation in pH values across the tubes, which prevents the investigator from establishing a clear baseline control group at neutral pH.

The use of potassium ions in Tube 3 instead of sodium ions, which would inhibit enzyme activity and cause the rate at pH 8.0 to be lower than it should be.

The change in the independent variable (pH) across the tubes, which makes it impossible to determine if the rate of starch hydrolysis is the dependent variable.

Show answer & explanation

Answer: The presence of chloride ions in the buffers for Tube 2 and Tube 3, which may artificially elevate the measured hydrolysis rates at pH 6.0 and pH 8.0.

Answer

The presence of chloride ions in the buffers for Tube 2 and Tube 3, which may artificially elevate the measured hydrolysis rates at pH 6.0 and pH 8.0.

The correct answer identifies chloride ions as the confounding variable. Because chloride ions stimulate amylase activity and are only present in the buffer systems of two of the treatment groups (Tubes 2 and 3), the rates of hydrolysis at pH

6.0

and

8.0

are artificially elevated, preventing an accurate comparison of the effect of pH alone.

Step-by-Step Solution

1

Identify the intended independent variable and the dependent variable.

The independent variable is pH (varying from

4.0

to

10.0

), and the dependent variable is the rate of starch hydrolysis.

This establishes what the experiment is designed to measure and helps isolate any unintended variables.

2

Analyze the buffer components for each tube to identify any differences that do not correlate with pH.

Tube 2 contains sodium chloride (supplying

Cl^-

ions) and Tube 3 contains Tris-HCl and potassium chloride (both supplying

Cl^-

ions), while Tube 1 and Tube 4 do not contain chloride components.

Any variable that differs systematically between experimental groups other than the independent variable is a potential confounding variable.

3

Evaluate the impact of the identified difference using the given scientific fact.

Since chloride ions stimulate amylase activity, their presence in Tubes 2 and 3 will increase the reaction rates in those tubes, making the rates at pH

6.0

and pH

8.0

appear higher due to the chloride ions rather than the pH alone.

This determines how the confounding variable distorts the experimental conclusions.

Key Concept

A confounding variable is an uncontrolled factor that varies systematically with the independent variable, making it impossible to determine whether the observed effects are due to the independent variable or the uncontrolled factor.

Question 70Question →

A student proposed the following hypothesis regarding the corrosion of iron:

*Hypothesis*: The mass of rust that forms on an iron nail submerged in a sodium chloride ( $NaCl$ ) solution for 7 days will increase continuously as the concentration of $NaCl$ in the solution increases from 0% to 10%.

To test this hypothesis, the student submerged identical iron nails in 5 different $NaCl$ solutions for 7 days and recorded the mass of the rust that formed on each nail. The results are shown in the table below:

$NaCl$ concentration (% by mass)	Mass of rust formed (mg)
0%	1.2
1%	3.5
3%	5.8
5%	4.2
10%	2.1

Based on these results, how should the student modify their hypothesis?

The student should modify the hypothesis to state that the mass of rust formed increases with

NaCl

concentration up to approximately 3%, but decreases at higher concentrations.

The student should modify the hypothesis to state that the mass of rust formed is inversely proportional to the

NaCl

concentration across all tested levels.

The student should modify the hypothesis to state that the mass of rust formed remains constant at all

NaCl

concentrations greater than 3%.

The student should retain the hypothesis without modification because the nail in the 10% solution produced more rust than the nail in the 0% solution.

Show answer & explanation

Answer: The student should modify the hypothesis to state that the mass of rust formed increases with $NaCl$ concentration up to approximately 3%, but decreases at higher concentrations.

Answer

The student should modify the hypothesis to state that the mass of rust formed increases with

NaCl

concentration up to approximately 3%, but decreases at higher concentrations.

The correct option accurately reflects the empirical data, which shows a rise in rust mass up to 3%

NaCl

concentration followed by a decline at higher concentrations. This requires a modification of the hypothesis from a continuous increase to a peaked relationship.

Step-by-Step Solution

1

Analyze the original hypothesis to identify the predicted trend.

The original hypothesis predicts that the mass of rust will continuously increase as the

NaCl

concentration increases from 0% to 10%.

This establishes the baseline expectation that must be compared against the actual data.

2

Examine the experimental data in the table to determine the actual trend.

As the concentration increases from 0% to 3%, the mass of rust increases from 1.2 mg to 5.8 mg. However, as the concentration increases further from 3% to 10%, the mass of rust decreases from 5.8 mg to 2.1 mg.

This identifies the pattern of the empirical evidence.

3

Compare the actual trend to the original hypothesis and determine the necessary modification.

Since the mass does not increase continuously but rather peaks at 3% and then decreases, the hypothesis must be modified to reflect this non-linear relationship (increasing up to a point, then decreasing).

This directly matches the learning objective of modifying a hypothesis based on new experimental data.

Key Concept

Formulating and Modifying Hypotheses

Question 71Question →

A student wants to modify an experiment measuring sugar solubility in water to determine the effect of higher temperatures ( $40^\circ\text{C}$ , $60^\circ\text{C}$ , and $80^\circ\text{C}$ ) on the mass of dissolved sugar. Arrange the steps of this modified procedure in the correct chronological order from start to finish.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of steps for the modified experiment is first heating the water to a target temperature, next adding sugar until it no longer dissolves, then measuring and recording the mass of the dissolved sugar, and finally repeating these steps for the other temperatures.

The correct order follows a logical experimental procedure for measuring solubility at different temperatures: first, establishing the independent variable (temperature) by heating the water; second, performing the test by adding sugar to saturation; third, measuring the dependent variable (mass of dissolved sugar); and fourth, repeating the process for other levels of the independent variable (other temperatures) while controlling other factors.

Step-by-Step Solution

1

Identify the first step in conducting a solubility test at a specific temperature.

The water sample must be heated to the target temperature (

40^\circ\text{C}

,

60^\circ\text{C}

, or

80^\circ\text{C}

) before adding sugar.

Dissolving sugar at the correct starting temperature ensures the solubility measurement is accurate for that temperature.

2

Determine the next physical step in the dissolution process.

Sugar is added incrementally and stirred until the solution becomes saturated.

Saturating the solution is necessary to find the maximum limit of solubility at that temperature.

3

Determine the measurement step that follows saturation.

Measure and record the total mass of sugar dissolved.

Recording the mass at the end of the trial provides the data point for that specific temperature.

4

Determine the final step to complete the study across the full temperature range.

Repeat the entire procedure for the remaining temperatures while keeping the water volume constant.

Testing all temperatures under controlled conditions allows for a valid comparison of solubility trends.

Key Concept

To modify an experiment to test a new range of an independent variable (temperature), one must systematically heat the solvent, dissolve the solute to saturation, measure the mass, and repeat the process under controlled conditions for all remaining values of the independent variable.

Question 72Question →

A student conducted an experiment to measure the rate of water loss from a certain plant species under different relative humidity levels. The experimental design is summarized in the table below:

Trial	Relative Humidity (%)	Temperature ( $^\circ\text{C}$ )	Plant Species	Exposure Time (hours)
1	20	25	Fern	2
2	40	25	Fern	2
3	60	25	Fern	2
4	80	25	Fern	2

Suppose the student wants to perform a follow-up experiment to determine how temperature affects the water loss of this same plant species. Which of the following modifications to the experimental design would best allow the student to isolate the effect of temperature?

Vary the temperature across trials while keeping the relative humidity, plant species, and exposure time constant.

Vary both the temperature and the relative humidity across trials while keeping the plant species and exposure time constant.

Vary the temperature and use a different plant species for each trial while keeping the relative humidity constant.

Vary the temperature across trials while increasing the exposure time for each increase in temperature.

Show answer & explanation

Answer: Vary the temperature across trials while keeping the relative humidity, plant species, and exposure time constant.

Answer

Vary the temperature across trials while keeping the relative humidity, plant species, and exposure time constant.

To investigate the effect of a new independent variable (temperature), that variable must be varied while holding all other variables constant. The correct option describes changing the temperature across trials while maintaining constant relative humidity, plant species, and exposure time, which successfully isolates the effect of temperature.

Step-by-Step Solution

1

Identify the goal of the follow-up experiment.

The goal is to determine the specific effect of temperature on water loss (transpiration).

This establishes temperature as the new independent variable.

2

Apply the rule of experimental control.

To isolate the effect of temperature, only temperature should vary, while all other potential independent variables (such as relative humidity, plant species, and exposure time) must remain constant.

Varying multiple factors simultaneously introduces confounding variables, which prevents a clear conclusion about which variable caused the change.

3

Evaluate the choices to find the one that varies only temperature.

The option to vary the temperature while holding relative humidity, plant species, and exposure time constant correctly isolates the variable of interest.

This aligns with proper scientific method and experimental design.

Key Concept

Scientific Control of Variables in Follow-Up Experiments

Question 73Question →

An environmental scientist investigated the relationship between water temperature and the concentration of dissolved oxygen (DO) at saturation. The scientist hypothesized that as water temperature increases, the concentration of DO at saturation also increases because higher temperatures increase the solubility of gases in water. To test this hypothesis, the scientist measured the DO concentration at saturation in water samples at five different temperatures. The results are presented in the table below.

Water Temperature ( $^\circ\text{C}$ )	Dissolved Oxygen Concentration ( $\text{mg/L}$ )
$5$	$12.8$
$15$	$10.1$
$25$	$8.3$
$35$	$6.9$
$45$	$5.9$

Based on these results, does the data support the scientist's hypothesis, and how should the hypothesis be revised?

No; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.

Yes; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation increases.

No; the revised hypothesis should state that changing the concentration of dissolved oxygen at saturation causes the water temperature to decrease.

No; the revised hypothesis should state that the concentration of dissolved oxygen at saturation remains constant regardless of water temperature.

Show answer & explanation

Answer: No; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.

Answer

No; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.

The scientist's hypothesis predicted that as temperature increases, the concentration of dissolved oxygen at saturation would also increase. However, the experimental results show that as the temperature increases from

5^\circ\text{C}

to

45^\circ\text{C}

, the concentration of dissolved oxygen decreases from

12.8\text{ mg/L}

to

5.9\text{ mg/L}

. Because the results show the opposite of the predicted trend, the hypothesis is not supported, and the revised hypothesis must state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.

Step-by-Step Solution

1

Identify the scientist's original hypothesis and its predicted outcome.

The original hypothesis predicts that an increase in water temperature results in an increase in dissolved oxygen (DO) concentration (a direct relationship).

Establishing the initial prediction allows direct comparison with the actual experimental data.

2

Analyze the trend shown in the experimental data table.

As the temperature increases from

5^\circ\text{C}

to

45^\circ\text{C}

, the DO concentration steadily decreases from

12.8\text{ mg/L}

to

5.9\text{ mg/L}

(an inverse relationship).

Determining the actual mathematical relationship between the variables reveals if the initial prediction was correct.

3

Determine if the hypothesis is supported and formulate the necessary revision.

The data contradicts the hypothesis, meaning it is not supported (No). The hypothesis must be revised to reflect the inverse trend: as water temperature increases, DO concentration at saturation decreases.

Hypotheses must be modified to align with experimental findings when those findings refute the initial prediction.

Key Concept

Formulating and Modifying Hypotheses

Estimated Time:1m 30s

Question 74Question →

A group of students designed several investigations to study how wind speed affects the rate of water evaporation. For each investigation, they set up two trials with different wind speeds. However, each setup introduced a distinct confounding variable or source of error. Match each experimental setup to the primary confounding variable or source of error that threatens its internal validity.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The experimental setups match their confounding variables as follows: Setup 1 matches with differences in thermal energy input; Setup 2 matches with differences in exposed liquid-gas interface area; Setup 3 matches with differences in solute concentration; Setup 4 matches with differences in total duration of evaporation.

Each experimental setup introduces a distinct uncontrolled variable: temperature variation corresponds to differences in thermal energy input; diameter differences correspond to exposed liquid-gas interface area; the presence of sodium chloride corresponds to solute concentration; and unequal trial lengths correspond to duration of evaporation.

Step-by-Step Solution

1

Analyze Setup 1, which places one beaker under warm ventilation air and the other in a cooler corner.

This setup introduces temperature differences.

Since temperature directly affects kinetic energy and evaporation rate, this represents differences in thermal energy input.

2

Analyze Setup 2, which uses a

10\text{ cm}

Petri dish and a

4\text{ cm}

beaker.

This setup introduces variations in the surface area of the water exposed to air.

Water evaporates only from its surface, so changing the diameter alters the exposed liquid-gas interface area.

3

Analyze Setup 3, which compares a sodium chloride (

\text{NaCl}

) solution to deionized water.

This introduces solute concentration variations.

Solutes lower the chemical potential of the solvent and lower the vapor pressure, affecting evaporation independent of wind.

4

Analyze Setup 4, which measures evaporation over

60\text{ minutes}

versus

120\text{ minutes}

.

This setup varies the duration of the trial.

Unequal time intervals prevent a direct comparison of total volume lost unless normalized, representing differences in total duration of evaporation.

Key Concept

An experimental design must control all variables except the independent variable (wind speed). Any uncontrolled variable that can affect the dependent variable (evaporation rate) is a confounding factor that introduces potential error.

Estimated Time:2m 30s

Question 75Question →

An investigator conducted two experiments to study the factors affecting the rate of a chemical reaction between zinc metal ( $\text{Zn}$ ) and hydrochloric acid ( $\text{HCl}$ ).

In Experiment 1, the investigator added $1.0\text{ g}$ of zinc powder to $50\text{ mL}$ of $1.0\text{ M}$ $\text{HCl}$ solution in a beaker. The reaction was carried out at different temperatures ( $20^\circ\text{C}$ , $30^\circ\text{C}$ , $40^\circ\text{C}$ , and $50^\circ\text{C}$ ), and the time required for the zinc to completely dissolve was recorded for each trial.

In Experiment 2, the investigator added $1.0\text{ g}$ of zinc powder to $50\text{ mL}$ of $\text{HCl}$ solution of different concentrations ( $0.5\text{ M}$ , $1.0\text{ M}$ , $1.5\text{ M}$ , and $2.0\text{ M}$ ) in a beaker. The reaction was carried out at a constant temperature of $20^\circ\text{C}$ , and the time required for the zinc to completely dissolve was recorded for each trial.

Based on the descriptions of these experimental designs, is the statement that 'the temperature of the reaction was varied in Experiment 1 but was kept constant in Experiment 2' true or false?

True

False

Show answer & explanation

Answer: True

Answer

true

In Experiment 1, the investigator changed the temperature across trials (

20^\circ\text{C}

,

30^\circ\text{C}

,

40^\circ\text{C}

, and

50^\circ\text{C}

), which means temperature was varied. In Experiment 2, the investigator maintained a constant temperature of

20^\circ\text{C}

for all trials while varying the concentration of the acid. This directly confirms that temperature was varied in Experiment 1 and kept constant in Experiment 2, making the statement true.

Step-by-Step Solution

1

Analyze the role of temperature in Experiment 1.

The temperature was set to

20^\circ\text{C}

,

30^\circ\text{C}

,

40^\circ\text{C}

, and

50^\circ\text{C}

across different trials, which means it was varied.

To identify if temperature was an independent variable or a constant in the first experimental design.

2

Analyze the role of temperature in Experiment 2.

The temperature was kept at

20^\circ\text{C}

for all trials, which means it was kept constant.

To identify if temperature was an independent variable or a constant in the second experimental design.

3

Evaluate the statement using the findings from Steps 1 and 2.

The statement claims temperature was varied in Experiment 1 and kept constant in Experiment 2. Since this matches our analysis, the statement is true.

To determine the final truth value of the target statement.

Key Concept

Distinguishing between independent variables and controlled constants across multiple experimental setups.

Estimated Time:45s

Question 76Question →

A student proposed the following hypothesis regarding electrical circuits:

*Hypothesis*: As the cross-sectional area of a metal wire increases, its electrical resistance will increase because a larger wire contains more atoms that collide with and resist the flow of electrons.

To test this hypothesis, the student measured the electrical resistance of four copper wires, each $10\text{ m}$ long but with different diameters, at a constant temperature of $20^\circ\text{C}$ . The results are shown in the table below:

Wire	Diameter ( $\text{mm}$ )	Cross-sectional area ( $\text{mm}^2$ )	Resistance ( $\Omega$ )
1	0.5	0.20	4.00
2	1.0	0.79	1.00
3	1.5	1.77	0.44
4	2.0	3.14	0.25

Based on these results, how should the student modify the hypothesis?

The student should modify the hypothesis to state that as the cross-sectional area of a wire increases, its electrical resistance decreases.

The student should modify the hypothesis to state that the electrical resistance of a wire is independent of its cross-sectional area.

The student should keep the hypothesis as written because the wire with the largest cross-sectional area (

3.14\text{ mm}^2

) had the lowest resistance (

0.25\ \Omega

).

The student should modify the hypothesis to state that as the diameter of a wire decreases, its electrical resistance decreases.

Show answer & explanation

Answer: The student should modify the hypothesis to state that as the cross-sectional area of a wire increases, its electrical resistance decreases.

Answer

The student should modify the hypothesis to state that as the cross-sectional area of a wire increases, its electrical resistance decreases.

The correct answer states that the hypothesis should be modified to show that as the cross-sectional area of a wire increases, its electrical resistance decreases. The table shows that as the cross-sectional area increases from

0.20\text{ mm}^2

to

3.14\text{ mm}^2

, the resistance decreases from

4.00\ \Omega

to

0.25\ \Omega

. Since the initial hypothesis predicted that resistance would increase as cross-sectional area increases, the experimental results contradict the hypothesis. Therefore, the hypothesis must be modified to reflect this inverse relationship.

Step-by-Step Solution

1

Analyze the student's initial hypothesis.

The initial hypothesis states that larger cross-sectional area leads to higher resistance (a direct relationship).

To evaluate the hypothesis, we must first define the expected relationship between the variables.

2

Examine the experimental data in the table to determine the actual relationship between cross-sectional area and resistance.

As the cross-sectional area increases from

0.20\text{ mm}^2

to

3.14\text{ mm}^2

, the resistance decreases from

4.00\ \Omega

to

0.25\ \Omega

.

Comparing the independent variable (cross-sectional area) with the dependent variable (resistance) reveals the empirical trend.

3

Compare the empirical trend with the initial hypothesis and select the correct modification.

The empirical trend is inverse (area increases, resistance decreases), which contradicts the hypothesized direct relationship. Therefore, the hypothesis must be modified to state that resistance decreases as cross-sectional area increases.

A scientific hypothesis must be modified when experimental evidence consistently contradicts its predictions.

Key Concept

Evaluating and modifying a hypothesis based on conflicting experimental data.

Estimated Time:1m 30s

Question 77Question →

To study thermal expansion in solids, a researcher proposed that the coefficient of linear expansion ( $\alpha$ ) of a metal rod depends on its starting length. Specifically, the researcher hypothesized that longer rods of the same metal would exhibit a larger value of $\alpha$ when subjected to the same temperature change.

To test this hypothesis, the researcher measured the physical expansion of three copper rods under identical heating conditions. The results of the measurements and the calculated values of $\alpha$ are recorded in the table below.

Copper Rod	Initial Length ( $L_0$ , $\text{m}$ )	Temperature Increase ( $\Delta T$ , $^\circ\text{C}$ )	Expansion ( $\Delta L$ , $\text{mm}$ )	Coefficient of Linear Expansion ( $\alpha$ , $10^{-6}\text{ }^\circ\text{C}^{-1}$ )
Rod A	1.0	50	0.85	17
Rod B	2.0	50	1.70	17
Rod C	3.0	50	2.55	17

Based on the results of the experiment, does the data support the researcher's hypothesis, and how should the hypothesis be modified?

Yes; the data show that the total expansion of the rod increases from

0.85\text{ mm}

to

2.55\text{ mm}

as the initial length increases.

Yes; the data show that the coefficient of linear expansion increases proportionally with the initial length of the copper rod.

No; the data show that the coefficient of linear expansion decreases as the initial length of the rod increases.

No; the data show that the coefficient of linear expansion remains constant at

17 \times 10^{-6}\text{ }^\circ\text{C}^{-1}

regardless of the rod's initial length.

Show answer & explanation

Answer: No; the data show that the coefficient of linear expansion remains constant at $17 \times 10^{-6}\text{ }^\circ\text{C}^{-1}$ regardless of the rod's initial length.

Answer

The experimental data does not support the hypothesis because the coefficient of linear expansion remains constant at

17 \times 10^{-6}\text{ }^\circ\text{C}^{-1}

for all initial lengths, meaning the hypothesis should be modified to state that the coefficient of linear expansion is independent of the initial length of the rod.

The correct option accurately states that the hypothesis is not supported because the coefficient of linear expansion (

\alpha

) remains constant at

17 \times 10^{-6}\text{ }^\circ\text{C}^{-1}

for all three rods, regardless of their initial length. A scientific hypothesis must be rejected or modified when the measured property does not change in the predicted direction.

Step-by-Step Solution

1

Identify the core assertion of the researcher's hypothesis.

The hypothesis predicts that as the initial length (

L_0

) of a metal rod increases, the coefficient of linear expansion (

\alpha

) of that metal will also increase.

Understanding the hypothesis defines the independent variable (initial length) and the dependent variable (coefficient of linear expansion) that must be compared using the data.

2

Analyze the data table to observe how the coefficient of linear expansion (

\alpha

) behaves as the initial length increases.

As the initial length increases from

1.0\text{ m}

to

2.0\text{ m}

and then

3.0\text{ m}

, the calculated coefficient of linear expansion (

\alpha

) remains constant at

17 \times 10^{-6}\text{ }^\circ\text{C}^{-1}

.

Evaluating the trend of the target variable (

\alpha

) against the independent variable (

L_0

) determines whether the hypothesis is supported or refuted.

3

Determine the proper modification of the hypothesis based on the constant values of

\alpha

.

Since

\alpha

did not increase, the hypothesis is refuted. The modified hypothesis must reflect that the coefficient of linear expansion remains constant and is independent of the initial length of the rod.

Comparing the empirical data directly to the proposed hypothesis allows the researcher to correctly modify it to align with the experimental results.

Key Concept

Formulating and Modifying Hypotheses

Estimated Time:1m 15s

Question 78Question →

Students conducted two experiments to study the growth of *Arabidopsis thaliana* plants over a 30-day period.

Experiment 1
Five groups of 10 plants were grown in identical pots containing the same soil type. Each group received a different concentration of Fertilizer X (0%, 1%, 2%, 3%, or 4% by volume) dissolved in water. All plants were kept under continuous white light at a constant temperature of 22°C and watered daily with 50 mL of their respective solution. The average height of the plants in each group was measured at the end of 30 days.

Experiment 2
Five groups of 10 plants were grown under the same conditions as in Experiment 1, except that all plants received a 2% solution of Fertilizer X, and each group was exposed to a different color of light (blue, green, red, yellow, or white).

Based on the descriptions of the two experiments, which of the following variables was kept constant in Experiment 1 but was varied in Experiment 2?

The concentration of Fertilizer X

The color of light the plants received

The type of soil used to grow the plants

The duration of the growth period

Show answer & explanation

Answer: The color of light the plants received

Answer

The color of light the plants received

The correct answer is the color of light the plants received. In Experiment 1, all plants were kept under continuous white light (a constant condition). In Experiment 2, the light color was the independent variable, meaning it was varied (blue, green, red, yellow, or white) across the different groups of plants.

Step-by-Step Solution

1

Identify the independent variable (what is varied) and the constants (what is kept the same) in Experiment 1.

In Experiment 1, the fertilizer concentration is varied (0% to 4%), while the light color (white light), soil type, temperature (22°C), watering volume (50 mL), and duration (30 days) are kept constant.

This establishes the control parameters and experimental variable for the first study.

2

Identify the independent variable and the constants in Experiment 2.

In Experiment 2, the light color is varied (blue, green, red, yellow, white), while the fertilizer concentration (2%), soil type, temperature, watering volume, and duration are kept constant.

This establishes the control parameters and experimental variable for the second study.

3

Compare the two sets of variables to find which condition is constant in Experiment 1 but varied in Experiment 2.

Light color is constant in Experiment 1 (white light) but varied in Experiment 2 (different colors).

This directly answers the comparative question asked in the stem.

Key Concept

Comparing and Contrasting Multiple Experimental Designs

Estimated Time:45s

Question 79Question →

Suppose a student wants to modify an experiment measuring the evaporation rate of salt water ( $200\text{ mL}$ of $5\%$ saline solution heated by a $100\text{ W}$ heat lamp placed $30\text{ cm}$ above the beaker in a draft-free room) to determine the specific impact of wind speed on the evaporation rate, while ensuring that the thermal energy input and other variables remain controlled. Arrange the following steps in the correct chronological sequence to successfully conduct this follow-up experiment.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence is: first, prepare the three identical saline solution beakers; second, position the heat lamp and the variable-speed fan at fixed distances relative to the beaker; third, select the wind speed setting and start the fan and lamp; and fourth, record the mass of the beaker at ten-minute intervals over one hour.

The correct sequence begins with preparing the identical solutions to establish controlled initial parameters. Next, the physical apparatus must be positioned to control the heat lamp distance and fan distance. Then, the specific wind speed is chosen and the trial is started by turning on the equipment. Finally, the mass is measured at regular intervals to track the evaporation rate.

Step-by-Step Solution

1

Prepare identical samples to control initial conditions.

Three beakers with equal volume (

200\text{ mL}

) and concentration (

5\%

) of saline solution.

Ensures that differences in evaporation are due only to the wind speed, not variations in initial volume or salinity.

2

Set up the physical apparatus with controlled physical dimensions.

The beaker, heat lamp (

30\text{ cm}

away), and fan (

50\text{ cm}

away) are positioned in a stable, repeatable configuration.

Ensures the heat energy delivered to the solution is constant across all trials, and the fan's physical distance does not vary.

3

Apply the independent variable (wind speed) and start the experimental conditions.

The trial begins under a specific, constant wind speed with simultaneous heating.

Allows the evaporation process to begin under the selected test condition.

4

Measure and record the dependent variable over the specified duration.

Mass data at

10

,

20

,

30

,

40

,

50

, and

60

minutes.

Provides the raw data necessary to calculate the rate of mass loss (evaporation rate) over time for that specific wind speed.

Key Concept

Designing a controlled follow-up experiment requires isolating the new independent variable (wind speed) by maintaining all original variables (lamp distance, initial salinity, and volume) constant, and sequencing the steps from sample preparation to final measurement.

Question 80Question →

A scientist conducted two experiments to study soil respiration (measured as the rate of carbon dioxide release, $R_s$ , in $\text{g CO}_2/\text{m}^2/\text{day}$ ) from a forest soil sample under different conditions.

Experiment	Soil Temperature ( $^\circ\text{C}$ )	Soil Moisture Content (SMC)	Observed Trend in $R_s$
1	$20^\circ\text{C}$ (constant)	Varied ( $10\%$ , $20\%$ , $30\%$ )	$R_s$ increases as SMC increases
2	Varied ( $15^\circ\text{C}$ , $25^\circ\text{C}$ , $35^\circ\text{C}$ )	$20\%$ (constant)	$R_s$ increases as temperature increases

Suppose a scientist wants to determine if the positive relationship between SMC and $R_s$ observed at $20^\circ\text{C}$ remains positive at a near-freezing temperature of $2^\circ\text{C}$ . Which of the following modifications to the experimental design would best allow the scientist to test this hypothesis?

Measure

R_s

of soil samples at a constant temperature of

2^\circ\text{C}

while varying the SMC at

10\%

,

20\%

, and

30\%

.

Measure

R_s

of soil samples as the temperature is decreased from

20^\circ\text{C}

to

2^\circ\text{C}

while keeping the SMC constant at

20\%

.

Measure

R_s

of soil samples at temperatures of

2^\circ\text{C}

,

10^\circ\text{C}

, and

20^\circ\text{C}

while allowing the SMC to vary freely for each sample.

Measure the rate of water evaporation from the soil samples at

2^\circ\text{C}

as the SMC is varied at

10\%

,

20\%

, and

30\%

.

Show answer & explanation

Answer: Measure $R_s$ of soil samples at a constant temperature of $2^\circ\text{C}$ while varying the SMC at $10\%$ , $20\%$ , and $30\%$ .

Answer

Measure

R_s

of soil samples at a constant temperature of

2^\circ\text{C}

while varying the SMC at

10\%

,

20\%

, and

30\%

.

To determine if the positive relationship between soil moisture content (SMC) and soil respiration rate (

R_s

) is preserved at a new constant temperature (

2^\circ\text{C}

), the scientist must isolate SMC as the independent variable. This is accomplished by holding the temperature constant at

2^\circ\text{C}

and measuring

R_s

across the same range of SMC values (

10\%

,

20\%

, and

30\%

) used in the original experiment.

Step-by-Step Solution

1

Identify the goal of the proposed follow-up experiment.

The goal is to determine if the positive relationship between SMC and

R_s

holds at

2^\circ\text{C}

.

Understanding the hypothesis is necessary to determine which variables must be manipulated and measured.

2

Identify the independent and dependent variables required to test the hypothesis.

The independent variable must be SMC (varied at

10\%

,

20\%

, and

30\%

) and the dependent variable must be

R_s

(soil respiration rate).

To see if the relationship between moisture and respiration is altered, moisture must be varied while measuring respiration.

3

Identify the necessary control variables.

The temperature must be held constant at the new temperature of interest (

2^\circ\text{C}

).

If temperature is not held constant at

2^\circ\text{C}

, the effect of temperature will confound the results.

4

Select the option that matches these design criteria.

Varying SMC while maintaining a constant temperature of

2^\circ\text{C}

and measuring

R_s

is the correct experimental design.

This setup isolates the effect of SMC at the specific temperature of

2^\circ\text{C}

without introducing confounding variables.

Key Concept

To test the relationship between an independent variable and a dependent variable under a new constant condition, the independent variable must be varied while keeping all other conditions constant.

Estimated Time:2m 0s

Experimental Design and Scientific Method

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept