# What mass of copper can be displaced by an excess of magnesium from a solution of copper chloride2

What mass of copper can be displaced by an excess of magnesium from a solution of copper chloride2 weighing 268 g rram with a mass fraction of salt of 10%.

1.Let’s find the mass of copper (II) chloride in solution.
Mass fraction of a substance is calculated by the formula:
W = m (substance): m (solution) × 100%,
m (substance) = (m (solution) × W): 100%,
m (substance) = (268 g × 10%): 100% = 26.8 g.
2.Let’s find the amount of copper chloride substance by the formula:
n = m: M.
M (CuCl2) = 64 + 71 = 135 g / mol.
n = 26.8 g: 134 g / mol = 0.198 mol.
3. Let’s compose the reaction equation, find the quantitative ratios of substances.
CuCl2 + Mg = MgCl2 + Cu ↓.
According to the reaction equation, 1 mol of copper chloride accounts for 1 mol of copper. The substances are in quantitative ratios of 1: 1.
The amount of copper and copper chloride will be equal.
n (CuCl2) = n (Cu) = 0.2 mol.
4. Let’s find the mass Cu.
m = n M.
M (Cu) = 64 g / mol.
m = 0.198 mol × 64 g / mol = 12.67 g.
Answer: m = 12.67 g.

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