Chemical and Ionic Equilibrium - Result Question 121
65. The $pH$ of blood stream is maintained by a proper balance of $H _2 CO _3$ and $NaHCO _3$ concentrations. What volume of $5 M$ $NaHCO _3$ solution should be mixed with a $10 $ $mL$ sample of blood which is $2 M$ in $H _2 CO _3$, in order to maintain a $pH$ of $7.4$? $\left(K _a\right.$ for $H _2 CO _3$ in blood is $7.8 \times 10^{-7}$ )
(1993, 2M)
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Answer:
Correct Answer: 65. $(80)$
Solution:
- Mixing $H _2 CO _3$ with $NaHCO _3$ results in buffer solution.
$pH=p K _a+\log \frac{\left[NaHCO _3\right]}{\left[H _2 CO _3\right]}=p K _a+\log \frac{n\left(NaHCO _3\right)}{n\left(H _2 CO _3\right)}$
$ \Rightarrow \quad 7.4=-\log \left(7.8 \times 10^{-7}\right)+\log \frac{x}{20} $
$\Rightarrow \quad x=400 $ $mmol$
$ NaHCO _3=5 \times V \Rightarrow V=80$ $ mL $
BETA
