A student proposed the following hypothesis regarding liquid evaporation: *Hypothesis*: Th… — ACT

A student proposed the following hypothesis regarding liquid evaporation:

*Hypothesis*: The rate of evaporation of a liquid is directly proportional to its boiling point because liquids with stronger intermolecular forces evaporate more rapidly at a constant temperature of $25^\circ\text{C}$ .

To test this hypothesis, the student placed equal volumes of three different liquids in identical open beakers. The beakers were kept in a temperature-controlled room at $25^\circ\text{C}$ and $1\text{ atm}$ of pressure. The volume of liquid remaining in each beaker was measured over a $24$ -hour period to determine the average evaporation rate. The boiling points and measured evaporation rates are shown in the table below.

Liquid	Boiling Point ( $^\circ\text{C}$ )	Average Evaporation Rate (mL/hr)
Acetone	$56$	$4.2$
Ethanol	$78$	$1.8$
Water	$100$	$0.5$

Based on these results, which of the following statements best describes how the student should modify their hypothesis?

The hypothesis should be modified to state that the rate of evaporation is inversely related to the boiling point of the liquid, because the liquid with the highest boiling point had the slowest evaporation rate.Answer
B
The hypothesis should be modified to state that the rate of evaporation is directly proportional to the boiling point of the liquid, because the liquid with the lowest boiling point had the slowest evaporation rate.
C
The hypothesis should be modified to state that the rate of evaporation is independent of the boiling point, because all three liquids evaporated at the same rate.
D
The hypothesis should be modified to state that the rate of evaporation is inversely related to the boiling point of the liquid, because acetone evaporated more slowly than water.

Answer

The hypothesis should be modified to state that the rate of evaporation is inversely related to the boiling point of the liquid, because the liquid with the highest boiling point had the slowest evaporation rate.

The experimental results show an inverse relationship between a liquid's boiling point and its evaporation rate: as the boiling point increases from

56^\circ\text{C}

100^\circ\text{C}

, the evaporation rate decreases from

4.2\text{ mL/hr}

0.5\text{ mL/hr}

. This contradicts the student's original hypothesis of a direct relationship. Therefore, the hypothesis must be modified to state that the rate of evaporation is inversely related to the boiling point, which is supported by the fact that water has the highest boiling point and the slowest evaporation rate.

Step-by-Step Solution

Analyze the student's original hypothesis and identify what it predicts.

The hypothesis predicts a direct relationship: higher boiling point leads to a faster evaporation rate.

Understanding the hypothesis is necessary to determine if the experimental data supports or refutes it.

Examine the relationship between boiling point and evaporation rate in the provided data table.

As the boiling point increases from

56^\circ\text{C}

78^\circ\text{C}

100^\circ\text{C}

, the evaporation rate decreases from

4.2\text{ mL/hr}

1.8\text{ mL/hr}

0.5\text{ mL/hr}

This step determines the actual trend shown by the empirical data.

Compare the data trend with the original hypothesis to formulate a modified hypothesis.

Because the evaporation rate decreases as the boiling point increases, the relationship is inverse, not direct. Water (highest boiling point) has the slowest evaporation rate, so the hypothesis must be modified to state that the evaporation rate is inversely related to the boiling point.

This allows selecting the statement that correctly describes the necessary modification and aligns with the data.

Key Concept

Evaluating and modifying a hypothesis based on experimental trends in data

Estimated Time:1m 30s

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