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  • 40 mL sample of 0.1 M solution of nitric acid is added to 20 mL of 0.3 M aqueous ammonia. What is the pH of resulting solution? (pKb = 4.75)  <div class='q

40 mL sample of 0.1 M solution of nitric acid is added to 20 mL of 0.3 M aqueous ammonia. What is the pH of resulting solution?
(pKb = 4.75)

 

Option: 1

5.04


Option: 2

8.95


Option: 3

7.65


Option: 4

89.5


Answers (1)

best_answer

 

\begin{array}{lll}{\mathrm{\ \ HNO}_{3}} \: {+} \:\: {\mathrm{NH}_{3} \longrightarrow \mathrm{NH}_{4} \mathrm{NO}_{3}} \\ {4 \ \mathrm{mmol}} \:\:\ \ {6 \mathrm{mmol}} \ \ \: \: \:\ \ {4 \mathrm{mmol }}\end{array}

\begin{array}{l}{\text { Since } W_{B}\left(\mathrm{NH}_{3}\right) \text { is left and salt }\left(\mathrm{NH}_{4} \mathrm{NO}_{3}\right) \text { is formed so a }} \\ {\text { is a basic buffer }} \\ {\text { Base left }=6-4=2 \mathrm{mmol}} \\ {\text { [Acid] }=40 \times 0.1=4 \mathrm{mmol}} \\ {[\mathrm{Base}]=20 \times 0.3=6 \mathrm{mmol}} \\ {\therefore \mathrm{pOH}=4.7447+\log 4 / 2=5.0457 \mathrm{\: and}} \\ {\mathrm{pH}=14-5.0457=8.95}\end{array}

Therefore option(2) is correct

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manish

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