1. Let’s write down the reaction equation:
2NaOH + H2SO4 = Na2SO4 + 2H2O.
2. Find the mass, and then the amount of sulfuric acid:
m (H2SO4) = (m (solution) * ω (H2SO4)) / 100% = 20 g * 4.9% / 100% = 0.98 g.
n (H2SO4) = m (H2SO4) / M (H2SO4) = 0.98 g / 98 g / mol = 0.01 mol.
3. Using the reaction equation, we find the amount of sodium hydroxide, and then its mass:
2n (NaOH) = n (H2SO4).
n (NaOH) = 0.5n (H2SO4) = 0.005 mol.
m (NaOH) = n (NaOH) * M (NaOH) = 0.005 mol * 40 g / mol = 0.2 g.
Answer: m (NaOH) = 0.2 g.
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