High School Chemistry : Help with Buffers

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

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Example Question #41 : Acids And Bases

A buffer solution is a solution that __________.

Possible Answers:

is slightly acidic and is used in laboratory settings to prevent chemical reactions from taking place

allows for a solution to easily change pH value without requiring great addition of strong acid or strong base

None of these

is slightly basic and is used in laboratory settings to prevent chemical reactions from taking place

consists of a mixture of a weak acid and its conjugate base, which resists change in pH

Correct answer:

consists of a mixture of a weak acid and its conjugate base, which resists change in pH

Explanation:

A buffer solution is used to keep the pH of the solution within a relatively narrow range. It must resist change in pH upon addition of acids or bases. A weak acid is used to lower the pH in response to addition of base or removal of acid, and its conjugate base is used to raise the pH in response to addition of acid or removal of base.

Example Question #42 : Acid Base Chemistry

Which of the following will increase the pH of an  buffer solution?

I. Removing carbonic acid

II. Adding sodium bicarbonate

Possible Answers:

II only

None of these

I only

Both I and II

Correct answer:

Both I and II

Explanation:

To answer this question we need to look at the reaction below:

An increase in the pH will result in a decrease in the concentration of hydrogen ions (). Using Le Chatelier’s principle we can find out which answer choices will decrease .

Removing carbonic acid will decrease the concentration of . To maintain equilibrium, the reaction will shift to the left and make more reactants from products; therefore, there will be a decrease in the  and an increase in pH.

Recall that salts like sodium bicarbonate, or , will dissociate in water and form ions. Sodium bicarbonate will form sodium () and bicarbonate () ions. This side reaction will result in an increase in the bicarbonate ion concentration. Le Chatelier’s principle will shift the equilibrium of the given reaction to the left and, therefore, decrease the . Adding sodium bicarbonate will increase the pH.

Example Question #43 : Acid Base Chemistry

Which of the following will increase the pH of an  buffer solution?

I. Removing carbonic acid

II. Adding sodium bicarbonate

Possible Answers:

II only

Both I and II

I only

None of these

Correct answer:

Both I and II

Explanation:

To answer this question we need to look at the reaction below:

An increase in the pH will result in a decrease in the concentration of hydrogen ions (). Using Le Chatelier’s principle we can find out which answer choices will decrease .

Removing carbonic acid will decrease the concentration of . To maintain equilibrium, the reaction will shift to the left and make more reactants from products; therefore, there will be a decrease in the  and an increase in pH.

Recall that salts like sodium bicarbonate, or , will dissociate in water and form ions. Sodium bicarbonate will form sodium () and bicarbonate () ions. This side reaction will result in an increase in the bicarbonate ion concentration. Le Chatelier’s principle will shift the equilibrium of the given reaction to the left and, therefore, decrease the . Adding sodium bicarbonate will increase the pH.

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