Discussion
A solution contains 9.8 g of H2SO4 . How much NaOH is required to completely neutralize it? (molar mass of NaOH = 40 g mol−1 )
Answer: C
8 g of NaOH is needed.
H2SO4 (molar mass 98 g mol−1) is dibasic, so each mole needs two moles of NaOH:
\[ \begin{aligned} n(\mathrm{H_{2}SO_{4}}) &= \frac{9.8}{98} = 0.1 \text{ mol} \\ n(\mathrm{NaOH}) &= 2 \times 0.1 = 0.2 \text{ mol} \\ m &= 0.2 \times 40 = 8 \text{ g} \end{aligned} \]
0.2 g is the number of moles of NaOH written as grams. Treating the acid as monobasic (a 1 : 1 ratio) would give 4 g, which is not offered, and 0.4 g, 1.2 g and 1.6 g do not come from the stoichiometry.
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