GRE Subject Test: Chemistry : pH

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

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Example Question #28 : Acid Base Chemistry

What is the molarity of a  solution that has a pH of ?

Possible Answers:

Correct answer:

Explanation:

The pH of the solution is , therefore the concentration would be . This solution is based on the equation,  and because hydrochloric is a strong acid, it can be assumed to completely dissociate in solution.

Example Question #1 : P H

What is the pH of a  solution of ?

Possible Answers:

Correct answer:

Explanation:

We need to calculate the pH of a   solution. There is one mole of  in every mole of , therefore:

The equation with the relationship between pH and pOH is:

We can calculate the pH by rearranging this equation: 

Another way of solving this problem is shown below. The equation with the relationship between  and  concentration is:

Rearrange this equation:

We can calculate the pH of this solution using the equation below:

Example Question #2 : P H

What is the pH of a  solution of ?

Possible Answers:

Correct answer:

Explanation:

First we need to calculate the  of the   solution. For every mole of  , there is double the number of moles of hydroxide ions:

The pOH can be calculated using the below equation:

The equation with the relationship between pH and pOH is below:

We can calculate the pH by rearranging this equation: 

Another way of solving this problem is shown below. The equation with the relationship between  and  concentration is:

Rearrange this equation:

We can calculate the pH of this solution using the equation below:

Example Question #3 : P H

Considering the  of  (hydrofluoric acid) is , what is the  of the base ?

Possible Answers:

Correct answer:

Explanation:

The relationship between  and  is:

 

Rearranging this equation gives:

In order to calculate the , we must use this relationship:

Example Question #4 : P H

What is the pH of a  solution of ?

Possible Answers:

Correct answer:

Explanation:

Below is the equilibria of  in an aqueous solution:

 is a strong acid so it completely ionizes in solution. It has a high  of 

There is 100% dissociation of , therefore the resulting  in solution equals to the concentration of original .

Example Question #5 : P H

What is the pH of a  solution of ?

Possible Answers:

Correct answer:

Explanation:

Below is the equilibria of  in an aqueous solution:

 is a strong base so it completely ionizes in solution. It has a high solubility product constant.

There is 100% dissociation of  , therefore the resulting  in solution equals to the concentration of original .

Example Question #6 : P H

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If  of  is reacted with  of , what is the pH if the total volume of the solution is 1 liter ?

Possible Answers:

Correct answer:

Explanation:

Based on the chemical equation,  and  react in a 1:1 mole ratio. Therefore, in order to find the pH of this solution you must first determine the difference in moles of the two reactants and the limiting reactant. The reactant in excess will determine the pH of the solution.

There  is in excess and the pH of the solution will be based on the moles of the excess .

 

Example Question #7 : P H

What is the pH of an aqueous solution with a  hydroxide ion concentration?

Possible Answers:

Correct answer:

Explanation:

We need to calculate the pH of a solution with a  hydroxide ion concentration. 

The equation with the relationship between pH and pOH is below:

We can calculate the pH by rearranging this equation:

Another way of solving this problem is shown below. The equation with the relationship between 

and  concentration is:

Rearranging this equation gives:

We can calculate the pH of this solution using the equation below:

Example Question #8 : P H

Considering the  for acetic acid  is , what is the  for acetate ?

Possible Answers:

Correct answer:

Explanation:

The equilibrium governing the dissolution of  in water is:

 is the conjugate acid of . In other words,  is the conjugate base of .

Using the relationship, , we can calculate the Kb.

By rearranging the equation we get:

Example Question #9 : P H

Determine the pH of a   solution.

Possible Answers:

Correct answer:

Explanation:

 is a strong acid and therefore completely ionizes in solution. Therefore, all the  ions dissociate in the  molecules in solutions according to the below chemical equation:

This means that the 

Below is the equation to calculate pH:

Therefore,

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