Question

calculate the molarity of 145.0 ml of a solution that is .92% by mass NaCl. Assume the density of the solution is the same as pure water

Answer 1

given

volume of solution = 145 ml

also

density of solution = density of pure water = 1 g/ml

now

we know that

mass = density x volume

so

mass of solution = 1 x 145

mass of solution = 145 ml

now

we know that

percent mass of NaCl = mass of NaCl x 100 / mass of solution

so

0.92 = mass of NaCl x 100 / 145

mass of NaCl = 1.334 g

now

we know that

moles = mass / molar mass

so

moles of NaCl = 1.334 / 58.44

moles of NaCl = 0.02282683

now

we know that

molarity = moles of solute (NaCl) x 1000 / volume of solution (ml)

so

molarity = 0.02282683 x 1000 / 145

molarity = 0.1574

so

the molarity of the solution is 0.1574 M