Question

What is the molarity of an $NaOH$ solution if 250 mL contains 1 mg of $NaOH$?

• A. ${10}^{-1}M$
• B. ${10}^{-2}M$
• C. ${10}^{-4}M$
• D. ${10}^{-3}M$

Answer 1

The correct option is C ${10}^{-4}M$

$\text{Number of moles of}NaOH=\frac{\text{given mass of}NaOH}{\text{molar mass}}=\frac{{10}^{-3}}{40}$

$\text{Molarity}=\frac{\text{number of moles of solute}}{\text{volume of solution in mL}}\times 1000$

$\text{Molarity}=\frac{\frac{{10}^{-3}}{40}\times 1000}{250}={10}^{-4}M$