Calculate the mass of the salt obtained by the interaction of magnesium with a solution of hydrochloric acid weighing 200 grams with a mass fraction of acid 7.3%.
Find the mass of hydrochloric acid in the solution.
W = m (substance): m (solution) × 100%, hence
m (substance) = (m (solution) × W): 100%.
m (substance) = (200 g × 7.3%): 100% = 14.6 g.
Let’s find the amount of hydrochloric acid substance by the formula:
n = m: M.
М (HCl) = 36.5 g / mol.
n = 14.6 g: 36.5 g / mol = 0.4 mol.
Let’s find the quantitative ratios of substances.
Mg + 2HCl → MgCl2 + H2
For 2 mol of HCl, there is 1 mol of the MgCl2 salt.
Substances are in quantitative ratios of 2: 1.
The amount of salt substance will be 2 times less than that of HCl.
n (MgCl2) = ½ n (HCl) = 0.4: 2 = 0.2 mol.
Let’s find the mass of salt.
m = n × M.
M (MgCl2) = 95 g / mol.
m = 95 g / mol × 0.2 mol = 19 g.
Answer: 19 g.
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