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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Chemistry
Chapter
Ionic Equilibrium

NTA Abhyas 2020 · Chemistry · Ionic Equilibrium

One litre of 1M solution of an acid HA ( K _ a = 10 ^ - 4 at 25 ^ o...

One litre of 1M\text{1}\text{M} solution of an acid HA(Ka=10−4at 25oC)haspH=2.Itisdilutedbywatersothenew\text{HA} \left({K}_{a} \text{=}{\text{10}}^{- \text{4}} \text{at 25}{}^{o} \text{C}\right) has \text{pH}\text{=}\text{2}\text{.} It is diluted by water so the newpHbecomesdouble.Thesolutionwasdilutedtobecomes double. The solution was diluted toy ×\times1{0}^{z}ml.Thevalueofy+z2. The value of \dfrac{y + z}{2}is:One litre of 1M solution of an acid HA ( K _ a = 10 ^ - 4 at 25 ^ o C) has pH=2. It is diluted by water so the new pH

Correct answer

5.5

Step-by-step solution

One litre of 1M solution of an acid HA ( K _ a = 10 ^ - 4 at 25 ^ o C) has pH=2. It is diluted by water so the new pH

pH=2⇒[H+]1=10−2=c1α1=1×α1pH = 2 ⇒ {\left[{H}^{+}\right]}_{1} = {10}^{- 2} = {c}_{1}{\alpha}_{1} = 1 \times {\alpha}_{1}

α1=10−2{\alpha}_{1} = {10}^{- 2}

pH=4⇒[H+]2=10−4=1×1000V×α2pH = 4 ⇒ {\left[{H}^{+}\right]}_{2} = {10}^{- 4} = \dfrac{1 \times 1000}{V} \times {\alpha}_{2}

ka=10−4=α22C21−α2=α2×α2×C21−α2{k}_{a} = {10}^{- 4} = \dfrac{{\alpha}_{2}^{2}{C}_{2}}{1 - {\alpha}_{2}} = \dfrac{{\alpha}_{2} \times {\alpha}_{2} \times {C}_{2}}{1 - {\alpha}_{2}}

10−4=α2×10−41−α2⇒α2=0.5{10}^{- 4} = \dfrac{{\alpha}_{2} \times {10}^{- 4}}{1 - {\alpha}_{2}} ⇒ {\alpha}_{2} = 0 .5

[H+]2=1×1000V×α2=10−4{\left[{H}^{+}\right]}_{2} = \dfrac{1 \times 1000}{V} \times {\alpha}_{2} = {10}^{- 4}

1×1000V×0.5=10−4\dfrac{1 \times 1000}{V} \times 0 .5 = {10}^{- 4}

V=5×106mlV = 5 \times {10}^{6}ml

⇒x+y2=5+62=112=5.5⇒ \dfrac{x + y}{2} = \dfrac{5 + 6}{2} = \dfrac{11}{2} = 5 .5
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