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Q.
The correct order of pH of solutions of $ \text{CuS}{{\text{O}}_{\text{4}}}\text{,NaCN,NaCl} $ and water is
EAMCETEAMCET 2009
Solution:
$ \text{CuS}{{\text{O}}_{\text{4}}} $ is a salt of weak base $ [CO{{(OH)}_{2}}] $ and strong acid $ ({{H}_{2}}S{{O}_{4}}), $ hence it will be acidic in nature. Therefore, pH of its solution must be less than 7. $ \text{NaCl} $ is a salt of strong base $ \text{(NaOH)} $ and strong acid $ \text{(HCl),} $ hence it will be neutral in nature. Therefore pH of its solution will be 7. Similarly, $ {{\text{H}}_{\text{2}}}\text{O} $ is neutral itself in nature, therefore its pH also will be 7. On the other hand, $ \text{NaCN} $ is a salt of strong base $ (\text{NaOH}) $ and weak acid $ \text{(HCN),} $ so its solution must be basic in nature showing pH greater than 7. Hence, correct order of pH is as follows : $ CuS{{O}_{4}}