GRE Subject Test: Chemistry : Acid-Base Chemistry

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

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Example Questions

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Example Question #61 : Acid Base Chemistry

HCN dissociates based on the following reaction.

The Ka for hydrogen cyanide is .

 of  is added to  of water. What is the pH of the resulting solution?

Possible Answers:

Correct answer:

Explanation:

Since HCN is a weak acid, we must use the equilibrium equation.

Because the HCN dissociates in solution, we expect the concentrations of protons and cyanide ions to increase, while the concentration of HCN will decrease. After determining the molarity of the solution, we can set up the equation below, using X as the amount of moles that dissociate.

Because X is small, we can neglect its impact in the denominator.

Since X is the concentration of protons in the solution, we can calculate the pH by using the equation .

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