ACT Science Practice: How to Understand “Weaken Hypothesis” Questions

ACT Science Practice: How to Understand “Weaken Hypothesis” Questions

On the Research Summaries passages on Test Day, you may see questions that ask about the hypotheses each experiment is based on – some will ask you to weaken and some will ask you to strengthen these hypotheses. For the weaken questions, you must fully understand the set-up behind the experiments in order to know whether the results will weaken a conclusion. Try to identify the purpose, method, and results for each experiment first to get better scores on the ACT Science Test. Here is a free ACT Science practice question to start practicing for the ACT right now!

 

Weaken Hypothesis Practice Question

The process of titration is an important tool in chemistry to use when trying to determine the concentration of an unknown.  While often restricted to acid and base neutralization, it can also be used in many applications when the concentration of an unknown needs to be established.  In order to use titration, one must know the concentration of one of the reactants as well as the volume of both reactants.  Normally, a chemical reaction is used in which a color change will indicate the end point of the titration.

Experiment 1

An experiment was set up as shown in Figure 1.  In Buret A is placed 15.0 ml of 0.2M H2SO4solution.  In Buret B is placed 50.0 ml of a potassium hydroxide (KOH) solution of unknown concentration.  The sulfuric acid is allowed to run into the Erlenmeyer flask and to the flask three drops of phenolphthalein are added.  The base is added drop by drop until the phenolphthalein turns a very faint pink color.  This is considered the end point of the titration.  The experiment is repeated three more times using other concentrations of potassium hydroxide (KOH).  The results of this experiment are summarized in Table 1.


Experiment 2


A second titration was done with a setup similar to that in Figure 1.  In this case, an iodine solution is placed in Buret A and various fruit juices are placed in Buret B.  Once the fruit juice was placed in the flask, several drops of a starch solution were added.  This solution would turn a blue-black color once the endpoint of the titration was reached.  The chemical reaction is as follows:

Ascorbic Acid + I2 → 2I- + dehydroascorbic acid

The results of this experiment are summarized on Table 2.

Question 1: One of the students doing Experiment 2 hypothesized that orange juice has the most Vitamin C of all the juices tested. Assuming that using more juice indicates the presence of more Vitamin C, is this hypothesis supported from the experiment?

A  No, since orange juice had the least Vitamin C and apple juice the most.

B  No, since orange juice had the least Vitamin C and cranberry juice the most.

C  Yes, since orange juice had the most Vitamin C and apple juice the least.

D  Yes, since orange juice had the most Vitamin C and grape juice the least.

Explanation

Since the total volume used is the difference between the starting and ending volumes, the orange juice actually has the least Vitamin C as 50.0 – 43.8 = 6.2. According to these results, the apple juice has the most Vitamin C. The answer is A.

Weaken hypotheses questions can also appear in Data Interpretation and Research Summaries passages. Make sure to always examine the point of view of the student/scientist/author. Ask yourself if the data supports their conclusions, or not.