Question

A solution is prepared by dissolving 5.85 g of NaCl (Molar mass = 58.5 g mol$^{-1}$) in water to make 500 mL of solution. The molarity of the solution is:

• A. 0.1 M
• B. 0.2 M
• C. 0.5 M
• D. 1.0 M

Hint:

If the volume is given in milliliters, you can use the combined formula for molarity to save time during the exam:
\[ M = \frac{\text{Weight of solute (g)} \times 1000}{\text{Molar mass of solute} \times \text{Volume of solution (mL)}} \]
Substituting: $M = \frac{5.85 \times 1000}{58.5 \times 500} = \frac{10 \times 1000}{100 \times 500} = 0.2\text{ M}$.

Answer 1

The Correct Option is B

Step 1: Moles.
moles $= 5.85/58.5 = 0.1$ mol
Step 2: Molarity.
$M = 0.1/0.5 = 0.2$ M
\[ \boxed{0.2 \text{ M}} \]