Question

Calculate the molarity of a solution containing 5g of NaOH in 450 mL solution .

• A. $0.278 \times 10^{-3} M$
• B. $0.278\ M$
• C. $2.78 \times 10^{-3} M$
• D. $2.78\ M$

Answer 1

Answer: (B)

$0.278\ M$

Answer 2

To calculate the molarity of a solution, we need to determine the number of moles of solute and divide it by the volume of the solution in liters.
Given:
Mass of NaOH = $5\ g$
Volume of solution = 450 mL = $0.450\ L$
First, we need to calculate the number of moles of NaOH. The molar mass of NaOH is approximately 40 g/mol ($22.99\ g/mol$ for Na + $16.00 \ g/mol$ for O + $1.01\ g/mol$ for H).
Number of moles of NaOH = $\frac {\text {Mass of NaOH}}{\text {Molar mass of NaOH}}$ = $\frac {5\ g }{40\ g/mol}$= $0.125\ mol$
Now we can calculate the molarity of the solution using the formula:
Molarity $(M) =\frac {\text {Moles of solute}}{\text {Volume of solution (in liters)}}$

Molarity $(M) = \frac {0.125\ mol }{0.450\ L} ≈ 0.278\ M$

Therefore, the molarity of the solution containing $5\ g$ of NaOH in $450\ mL$ solution is approximately $0.278 \ M$.