1. Tardigrade
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  4. A solution is prepared by mixing 0.01 mol each of H 2 CO 3, NaHCO 3, Na 2 CO 3, and NaOH in 100 mL of water. pH of the resulting solution is [Given: p K a 1 and p K a 2 of H 2 CO 3 are 6.37 and 10.32, respectively ; log 2=0.30 ]

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Q. A solution is prepared by mixing $0.01\, mol$ each of $H _2 CO _3, NaHCO _3, Na _2 CO _3$, and $NaOH$ in $100 \, mL$ of water. $pH$ of the resulting solution is ___
[Given : $p K _{ a 1}$ and $p K _{ a 2}$ of $H _2 CO _3$ are $6.37$ and $10.32$, respectively $; \log 2=0.30$ ]

JEE AdvancedJEE Advanced 2022

Solution:

image
Final mixture has 20 milli moles $NaHCO _3$ and 10 milli moles $Na _2 CO _3$
$ pH = pKa _2+\log \frac{\text { Salt }}{\text { Acid }} $
$ pH = pKa _2+\log \left(\frac{10}{20}\right) $
[Buffer : $Na _2 CO _3+ NaHCO _3$ ]
$ =10.32-\log 2=10.02$