The amount of calcium nitrate substance required to prepare 820 g of a solution with a mass fraction of 4% is

Find the mass of a substance
m (substance) = m (solution) * ω
m (substance) = 820 g * 0.04 = 32.8 g
Find the amount of substance
n = m / M
n = 32.8 / 164 = 0.2 (mol)

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