A 1.00 liter solution contains 0.44 moles hydrocyanic acid and 0.34 moles sodium cyanide .

Question

If 0.17 moles of nitric acid are added to this system, indicate whether the following statements are true or false. 

(Assume that the volume does not change upon the addition of nitric acid.) 

True/False A. The number of moles of HCN will increase. 

True/False B. The number of moles of CN^- will remain the same. 

True/False C. The equilibrium concentration of H₃O⁺ will decrease. 

True/False D. The pH will remain the same. 

True/False E. The ratio of [HCN] / [CN^-] will decrease.

Answer 1

This is a buffer system consisting of a weak acid, HCN and the salt of that acid, NaCN.

Upon addition of nitric acid (HNO3), HCN is formed and NaCN is used up.

HNO₃ + NaCN ==> NaNO₃ + HCN

A. True

B. False. The number of moles of CN^- will decrease b/c it is now part of HCN, a weak acid.

C. False. The [H₃O⁺] will increase slightly.

D. False. The pH will decrease slightly because acid is being added and being converted to HCN

E. False. It will increase.