chemistry ques?

Question

If 11.10 grams of KCl are dissolved in water to make a solution of 0.153 L, the density is found to be 1.053 g/cm3. Calculate the molality of the solute.

Answer 1

Molality can be found as,
Molality = moles of solute / kilograms of solution

You are given the mass of the solute, but you need to know the number of moles of solute. To find the number of moles of KCl, divide the mass given by the molar mass of Potassium Chloride.
Moles = mass / molar mass
Moles of KCl = (11.10 grams) / (74.55 g/mol)
Moles = .149 moles of KCl

You need to know the mass of the solution. You are given a volume of the final solution and its density, from this you can calculate its mass.
Density = mass / volume
Mass = Density * volume
We know that 1 cubic centimeter = 1 mL,
1 Liter = 1000 mL, so
Mass = (1.053 g/mL) * (153 mL)
Mass = 161.1 grams = .1611 kg

We now know all we need to know to calculate molality.
Molality = (.149 moles of KCl) / (.1611 kg)
Concentration = .925 molality