Pure elemental sodium metal weighing exactly was completely dissolved in distilled water, and the fi — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question
Question
Pure elemental sodium metal weighing exactly $0.115\text{ g}$ was completely dissolved in distilled water, and the final volume was made up to $400\text{ mL}$. Which of the following thermodynamic and stoichiometric statements are true regarding the resulting solution?
💡 Solution & Explanation
Step 1: Write the dissolution reaction. $Na(s) + H_2O(l) \rightarrow NaOH(aq) + 0.5 H_2(g)$. Step 2: Calculate initial moles of Sodium. $n = 0.115\text{ g} / 23\text{ g/mol} = 0.005\text{ mol}$. Step 3: Calculate product quantities. The reaction forms $0.005\text{ moles}$ of $NaOH$, making the solution basic (Option C is true). It produces $0.5 \times 0.005 = 0.0025\text{ moles}$ of $H_2$ gas (Option D is false). Step 4: Calculate Molarity and Normality. Molarity = $0.005\text{ mol} / 0.400\text{ L} = 0.0125\text{ M}$ (Option B is true). Since $NaOH$ has an n-factor of 1, Normality = Molarity = $0.0125\text{ N}$ (Option A is true).