Question

A 2.350×10−2 M solution of NaCl in water is at 20.0∘C. The sample was created by dissolving a sample of NaCl in water and then bringing the volume up to 1.000 L. It was determined that the volume of water needed to do this was 999.4 mL . The density of water at 20.0∘C is 0.9982 g/mL. Calculate the concentration of the salt solution in percent by mass.

Answer 1

A 2.350×10−2 M solution of NaCl in water is at 20.0∘C.

The sample was created by dissolving a sample of NaCl in water and then bringing the volume up to 1.000 L. It was determined that the volume of water needed to do this was 999.4 mL .

The density of water at 20.0∘C is 0.9982 g/mL. Calculate the concentration of the salt solution in percent by mass.

C = mass of Salt / Mass of solutino * 100%

initially

M = 2.35*10^-2

Volume of water = 999.4 mL

Volume of solution = 1 L = 1000 mL

Then...

mol of solute = M*V = 2.35*10^-2*1 = 2.35*10^-2 mol of solute = 0.0235 mol

mass of solute = mol*MW = 0.0235*58.44 = 1.37334 g of NaCl

mass of solvent = Density * V ol = 0.9982 g/mL *999.4 mL = 997.60108 g

Total mass = 1.37334 +997.60108 = 998.97442

% C = mass of salt / total mass = 1.37334 /998.97442 *100 = 0.13747% is salt per mass