A student investigates how the temperature of carbonic acid (H_2CO_3) affects the chemical… — ACT

A student investigates how the temperature of carbonic acid ( $H_2CO_3$ ) affects the chemical weathering of basalt. The student hypothesizes that as the temperature of the acid solution increases, the rate of chemical weathering (measured as the mass of basalt dissolved over a 24-hour period) will increase. The student performs four trials, starting with a $50.0\text{ g}$ sample of basalt in each trial, while keeping the acid volume and concentration constant. The results are shown in the table below:

Trial	Temperature (°C)	Final mass of basalt (g)
1	15	48.5
2	25	46.8
3	35	45.2
4	45	43.7

Based on the student's hypothesis, if a fifth trial were conducted at $55^\circ\text{C}$ under the same conditions, what would be the predicted final mass of the basalt sample?

A
Between $43.7\text{ g}$ and $45.2\text{ g}$
Less than $43.7\text{ g}$ Answer
C
Exactly $48.5\text{ g}$
D
Greater than $50.0\text{ g}$

Answer

Less than

43.7\text{ g}

According to the student's hypothesis, as temperature increases, the rate of weathering increases, meaning more basalt dissolves over 24 hours. Because the initial mass of basalt is constant at

50.0\text{ g}

, a higher dissolution rate results in a lower final mass of basalt. Since

55^\circ\text{C}

is higher than the maximum tested temperature of

45^\circ\text{C}

, the final mass at

55^\circ\text{C}

must be less than the final mass measured at

45^\circ\text{C}

(

43.7\text{ g}

). Therefore, the predicted final mass is less than

43.7\text{ g}

Step-by-Step Solution

Analyze the student's hypothesis.

The hypothesis states that as temperature increases, the rate of chemical weathering (mass of basalt dissolved) increases.

This establishes the direct relationship between temperature and dissolution rate.

Relate dissolution rate to the final mass of basalt.

Since each trial begins with

50.0\text{ g}

of basalt, a higher dissolution rate (more basalt dissolved) will result in a lower remaining final mass.

This translates the hypothesis about dissolution rate into a prediction about the measured variable (final mass).

Predict the final mass at

55^\circ\text{C}

relative to the existing data points.

A temperature of

55^\circ\text{C}

is higher than the highest tested temperature of

45^\circ\text{C}

(which had a final mass of

43.7\text{ g}

). According to the hypothesis, more dissolution must occur at

55^\circ\text{C}

than at

45^\circ\text{C}

, so the final mass must be less than

43.7\text{ g}

This applies the relationship to the target temperature value to find the correct range.

Key Concept

Formulating and testing predictions based on a scientific hypothesis.

Estimated Time:1m 0s

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