Answer to Question #267146 in General Chemistry for Mae

Question

1. Find the molality and molarity of the sample consisting 75% Copper and 25% Nickel by mass. The computed density of this sample is 0.00639 g/mm3.

Answer 1

1 mm3 = 1x10-6 L

density = 0.00639 g / mm3 x 1x10 mm3 / L = 6390 g / L = density of the metals

mass of Cu in 1 L = 75% x 6390 g/L = 4793 g

mols Cu = 4793 g x 1 mol / 63.6 g = 75.4 mols Cu

mass of Ni in 1 L = 25% x 6390 g/L = 1598 g

mols Ni = 1598 g x 1 mol / 58.7 g = 27.2 mols Ni

volume of Cu = 0.75 L

volume of Ni = 0.25 L

volume H2O = 1 L = 0.1 L = 0.900 L

mass H2O = 0.900 kg

molality Cu = mols Cu / kg H2O = 75.4 mol / 0.90 kg = 83.8 m

molality Ni = mols Ni / kg H2O =27.2 mol / 0.90 kg = 30.2 m

molarity Cu = mols Cu / L soln = 75.4 mol / 1 L = 75.4 M

molarity Ni = mols Ni / L soln = 27.2 mol / 1 L = 27.2 M