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JEE Main & Advanced Chemistry Equilibrium / साम्यावस्था Question Bank Hydrogenion concentration pH scale and buffer solution

  • question_answer
    The ionization constant of a certain weak acid is \[{{10}^{-4}}\]. What should be the [salt] to [acid] ratio if we have to prepare a buffer with pH = 5 using this acid and one of the salts                 [CPMT 2000; KCET 2000; Pb. CET 2000]

    A)                 \[1:10\]               

    B)                 \[10:1\]

    C)                 \[5:4\]  

    D)                 \[4:5\]

    Correct Answer: B

    Solution :

               \[pH=-\log {{K}_{b}}+\log \frac{[\text{salt}]}{\text{ }\!\![\!\!\text{ acid }\!\!]\!\!\text{ }}\]                    \[5=-\log {{10}^{-4}}+\log \frac{[\text{salt}]}{\text{ }\!\![\!\!\text{ acid }\!\!]\!\!\text{ }}\]                    \[\log \frac{[\text{salt}]}{\text{ }\!\![\!\!\text{ acid }\!\!]\!\!\text{ }}=1\]                                 \[\frac{[\text{salt}]}{\text{ }\!\![\!\!\text{ acid }\!\!]\!\!\text{ }}=\text{antilog}\,1=10:1\]


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