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1 L buffer of 0.1 mol NH3 and 0.1 mol NH4Cl: pH (or change in pH) after adding HCl

The same question, asked 2 times: 25 Jan 2023*, 7 Apr 2025. Every wording below, oldest first.

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  1. Question 1

    25 Jan 2023

    60
    A litre of buffer solution contains 0.1 mole of each of NH3NH_{3} and NH4ClNH_{4}Cl. On the addition of 0.02 mole of HClHCl by dissolving gaseous HClHCl, the pHpH of the solution is found to be [Given: pKb(NH3)=4.745pK_{b}\left( NH_{3} \right)= 4.745
    log⁡2=0.301log⁡3=0.477T=298 K]\begin{matrix} & \log2 = 0.301 \\ & \log3 = 0.477 \\ & T= 298\text{ }K\rbrack \end{matrix}

  2. Question 2

    7 Apr 2025

    121
    One litre buffer solution was prepared by adding 0.10 mol each of NH3{NH}_{3} and NH4Cl{NH}_{4}Cl in deionised water. The change in pH on addition of 0.05 mol of HCl to the above solution is ____\_\_\_\_ ×10−2\times 10^{- 2}. (Nearest integer) (Given : pKb{pK}_{b} of NH3=4.745{NH}_{3} = 4.745 and log⁡103=0.477\log_{10}3 = 0.477 ).