1. Tardigrade
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  3. Chemistry
  4. 100 mL of a buffer solution contains 0.1 M each of weak acid HA and salt NaA. How many gram of NaOH should be added to the buffer so that its pH will be 6 ? (K a . of .HA =10-5)

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Q. $100 \,mL$ of a buffer solution contains $0.1 \,M$ each of weak acid $HA$ and salt $NaA$. How many gram of $NaOH$ should be added to the buffer so that its $pH$ will be $6 $ ? $\left(K_{ a }\right.$ of $\left.HA =10^{-5}\right)$

Equilibrium

Solution:

For acidic buffer, $pH = pK _{ a }+\log \frac{0.1}{0.1}$

$pH = pKa =-\log \left(10^{-5}\right)=5$

Rule: ABA (In acidie buffer (A), on addition of $S_{B}(B)$, the concentration of $W_{A}($ A) decreases and that of salt increases). Let $x M$ of $NaOH$ is added.

$ pH _{\text {new }} =5+\log \left(\frac{0.1+x}{0.1-x}\right)$

$6-5 =\log \left(\frac{0.1+x}{0.1-x}\right) $

$\left(\frac{0.1+x}{0.1-x}\right)=$ Anti $\log (1)=10$

Solve for $x$ :

$ x=0.082\, M =\frac{0.082}{1000} \times 100$

$=0.0082 \,mol (100 \,mL )^{-1}$

$=0.0082 \times 40 \,g (100 \,mL )^{-1}=0.328 \,g $