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ACT Question for April 20th

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.

Assuming that the molarity of H2SO4 = amount of KOH, which formula would calculate the molarity of the base in Trial 1?

This is not the credited response. 

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This is not the credited response. 

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Question ID: 5889