JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ia164
The solubility of each salt is compared in a buffer of pH 3.0 and in a buffer of pH 7.0. Data: Ka(HF)=6.6×10−4; Ka(HCN)=6.2×10−10; HCl is a strong acid. Salts: AgCl, CaFX2, AgCN. Which statements are correct?
AThe solubility of AgCl at pH 3.0 is more than 5% greater than at pH 7.0.
BThe solubility of AgCN at pH 3.0 is about 100 times that at pH 7.0.
CThe solubility of CaFX2 at pH 3.0 is more than 10 times that at pH 7.0.
DThe increase for AgCN is larger than the increase for CaFX2.
Answer: B, D
Chloride is the conjugate base of a strong acid, so the solubility of AgCl does not change with pH. For AgCN, s=Ksp(1+[HX+]/Ka), ratio =(1+10−3/6.2e−10)/(1+10−7/6.2e−10)=100. For CaFX2, s∝α−2/3 with α=Ka/(Ka+[HX+]): α(7)=0.9998, α(3)=0.3976, ratio =1.85, only about 1.8, not above 10.