The molarity formula can be used to solve for the number of moles in a solution or the volume of a solution.

The guided practice below models how to set up and solve different types of molarity problems. Complete the solutions by typing in the missing numbers. If you need help, click the “hint” button. Then try a similar problem on your own and check your answer. Remember your significant figure rules! You can find these rules in the reference materials.

Sample Problem 1:

0.457 mol of MgSO₄ is dissolved in 0.56L of water. What is the molarity of the solution?

Solution Steps:

On Your Own Problem:

What is the molarity of a solution with 1.37 mol of NaCl dissolved in 2.4L of solution?

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Check Your Answer

1.37 mol NaCl / 2.4L = 0.57 M

Sample Problem 2:

What is the molarity of a solution made with 50.0g LiCl dissolved in 455mL of solution?

Solution Steps:

• Convert from grams → moles using the formula mass. (Use the Periodic Table to help you.)
• Use dimensional analysis to convert from mL → L.
• Use dimensional analysis and the molarity formula to solve for molarity.

On Your Own Problem:

A student carefully measures out 93.4g of CuCl₂ and fully dissolves it in water producing 1.2L of solution. What is the molarity of the CuCl₂ solution?

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Check Your Answer

Sample Problem 3:

How many moles of NaCl are in 257mL of a 0.3M NaCl solution?

Solution Steps:

• Convert from mL → L.
• 0.3 M = 0.3 mol / 1L.
• Use the formula to solve for the number of moles.

On Your Own Problem:

How much K₂SO₄ needs to be weighed out to create 30 mL of a 5.0 M K₂SO₄ solution?

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Check Your Answer