Question

$0.004gNaOH$ is dissolved in $250mL$ of solution
Then choose the correct statement(s):

• A. $\text{Molarity}=4\times {10}^{-4}M$
• B. $2\times \text{Normality}=\text{Molarity}$
• C. $\text{Concentration of}NaOH\text{solution}is16\text{ppm (w/V)}$
• D. $\text{Concentration of}NaOH\text{solution}is4\text{ppm (w/V)}$

Answer 1

Answer: (A), (C)

$\text{Concentration of}NaOH\text{solution}is16\text{ppm (w/V)}$

Molarity is the moles of solute (here NaOH) dissolved per litre of solution.

$\text{Molecular weight of}NaOH=23+16+1=40gmo{l}^{-1}$
$\text{Moles of}NaOH=\frac{0.004}{40}=1\times {10}^{-4}mol\text{Molarity}=\frac{1\times {10}^{-4}\times 1000}{250}=4\times {10}^{-4}M$
Since n-factor of NaOH is 1
and
$\text{Normality}=\text{Molarity}\times n_f$
$\Rightarrow \text{Normality}=\text{Molarity}$

$\text{Concentration of}NaOHinppm=\frac{\text{Weight of solute in g}}{\text{Volume of solution in mL}}\times {10}^6\Rightarrow \frac{0.004}{250}\times {10}^6=16\text{ppm}$