High School Chemistry  ·  Practice by Skill

Molarity and Solutions Practice Problems

A solution is a homogeneous mixture, and molarity tells you how much solute is dissolved in each liter of it. Most solution problems are a mole conversion plus a volume, so they reward careful unit work. Practice below covers molarity, dilution, solubility curves, molality, and freezing point depression.

What you’ll practice

  • Molarity: find moles of solute per liter of solution from a mass and a volume.
  • Dilution: use M1V1 = M2V2 to prepare a weaker solution from a stronger one.
  • Solubility and electrolytes: read solubility curves and tell strong electrolytes from weak ones.
  • Molality and colligative properties: calculate freezing point depression and boiling point elevation.

Learn the method first →

A quick example: making a dilution

How much 2.00 M stock solution do you need to make 250 mL of 0.100 M solution?

Use M1V1 = M2V2 and solve for V1: V1 = (0.100 M × 250 mL) ÷ 2.00 M.

You need 12.5 mL of stock, then add water to reach 250 mL total.

3 free molarity and solutions problems

Give each one a real try before you open the solution. Your answer is checked as soon as you submit it, and the worked solution shows every step so you can see exactly where a setup went wrong.

#1Molarity
What is the molarity of a solution made by dissolving 11.7 g of NaCl (M = 58.44 g/mol) in enough water to make 500.0 mL of solution?
#2Electrolytes
Which of the following is a strong electrolyte in aqueous solution?
#3Freezing Point Depression
You dissolve 58.4 g of NaCl (M = 58.44 g/mol) in 500.0 g of water. Calculate (a) the molality and (b) the new freezing point. (Kf = 1.86 °C·kg/mol; i = 2 for NaCl) Enter the freezing point.

Questions you might have about molarity and solutions

How do I calculate molarity?
Divide the moles of solute by the liters of solution. If you start with grams, convert to moles with the molar mass first, and convert milliliters to liters before dividing.
How does dilution work?
Adding solvent does not change the moles of solute, only the volume. That is why M1V1 = M2V2: the moles before and after are equal.
What is the difference between molarity and molality?
Molarity is moles of solute per liter of solution and changes slightly with temperature. Molality is moles of solute per kilogram of solvent and does not change, so it is used for freezing and boiling point problems.
What is a strong electrolyte?
A strong electrolyte breaks apart almost completely into ions in water, so the solution conducts electricity well. Soluble ionic compounds like NaCl and strong acids are strong electrolytes, while sugar and ethanol are nonelectrolytes.
High School Chemistry · Molarity and Solutions Practice Problems