Question

Calculate the normality of the solution containing 5 g of NaOH dissolved in 250 mL of aqueous solution.

• A. 0.5
• B. 1.0
• C. 0.1
• D. 0.05

Hint:

For monovalent compounds like $\text{NaOH}$, $\text{KOH}$, and $\text{HCl}$, Normality is exactly equal to Molarity. Here, Molarity = $(5/40) / 0.25 = 0.125 / 0.25 = 0.5\text{ M}$, so the Normality is also $0.5\text{ N}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Normality (\( N \)) is a concentration unit defined as the number of gram equivalents of solute dissolved per liter of solution.
For sodium hydroxide ($\text{NaOH}$), since it is a monovalent base (releases one $\text{OH}^-$ ion), its equivalent weight is equal to its molecular weight.
Key Formula or Approach:
1. Calculate the Equivalent Weight of \( \text{NaOH} \):
\[ \text{Equivalent Weight} = \frac{\text{Molecular Weight}}{\text{Acidity}} \]
For \( \text{NaOH} \), Molecular Weight = $23 (\text{Na}) + 16 (\text{O}) + 1 (\text{H}) = 40\text{ g/mol} $.
Since acidity = 1, Equivalent Weight = $40\text{ g/eq}$.
2. Calculate the Number of Gram Equivalents:
\[ \text{Gram Equivalents} = \frac{\text{Mass of Solute (g)}}{\text{Equivalent Weight}} \]
3. Calculate Normality (\( N \)):
\[ \text{Normality } (N) = \frac{\text{Gram Equivalents}}{\text{Volume of Solution (L)}} \]

Step 2: Detailed Explanation:
Let us perform the calculations:
Given:
Mass of \( \text{NaOH} = 5\text{ g} \)
Volume of solution = $250\text{ mL} = 0.25\text{ L}$
1. Calculate gram equivalents:
\[ \text{Gram Equivalents} = \frac{5\text{ g}}{40\text{ g/eq}} = 0.125\text{ eq} \]
2. Calculate normality:
\[ N = \frac{0.125\text{ eq}}{0.25\text{ L}} = 0.5\text{ eq/L} = 0.5\text{ N} \]

Step 3: Final Answer:
The normality of the solution is 0.5 N, which corresponds to option (A).