Let’s find the amount of MgO by the formula:
n = m: M.
M (MgO) = 40 g / mol.
n = 20 g: 40 g / mol = 0.5 mol.
Let’s compose the reaction equation, find the quantitative ratios of substances.
MgO + 2HNO3 = Mg (NO3) 2 + H2O.
For 1 mole of MgO, there is 1 mole of Mg (NO3) 2. Substances are in quantitative ratios 1: 1.
n (MgO) = n (Mg (NO3) 2) = 0.5 mol
Find the mass of Mg (NO3) 2:
m = n × M,
M (Mg (NO3) 2) = 148 g / mol.
m = 0.5 mol × 148 g / mol = 74 g.
Answer: 74 g.
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