Question

What are some examples of measuring concentration problems?

Answer 1

The Concentration of a solution can be measured in three different ways. (a) Molarity, M (b) Molality ,m and (c) Mole fraction, X.

Molarity (M) is the concentration of a solution expressed as the number of moles of solute per liter of solution:
Molarity (M) = moles solute / liters solution

To calculate molarity:
(a) Calculate the number of moles of solute present.
(b) Calculate the number of liters of solution present.
(c) Divide the number of moles of solute by the number of liters of solution.
What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?

(a) Calculate the number of moles of solute present.
mol NaOH = 15.0g NaOH x 1 mol NaOH / 40.0 g NaOH

mol NaOH = 0.375 mol NaOH

(b) Calculate the number of liters of solution present.
L soln = 225 mL x 1 L/ 1000mL

=0.225 L soln

(c) Divide the number of moles of solute by the number of liters of solution.
M = 0.375 mol NaOH / 0.225 L soln
= 1.67 M NaOH