1.Calculate the amount of magnesium oxide substance by the formula:
n = m: M, where M is molar mass.
M (MgO) = 24+ 16 = 40 g / mol.
n = 4 g: 40 g / mol = 0.1 mol.
2. Let’s compose the reaction equation:
MgO + 2 HNO3 = Mg (NO3) 2 + H2O.
According to the reaction equation, 1 mol of MgO accounts for 2 mol of nitric acid, that is, the substances are in quantitative ratios of 1: 2, the amount of nitric acid substance will be 2 times greater than the amount of magnesium oxide substance.
2n (MgO) = n (HNO3) = 0.1 × 2 = 0.2 mol.
3.Calculate the mass of nitric acid by the formula: m = n M,
M (HNO3) = 63 g / mol.
m = 63 g / mol × 0.2 mol = 12.6 g.
Answer: m = 12.6 g.
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