Question

Commercial concentrated aqueous ammonia is 28% NH3 by mass and has a density of 0.90 g/mL. You may want to reference (Pages 539 - 541) Section 13.4 while completing this problem. Part A What is the molarity of this solution?

Answer 1

Answer:

The molarity of this solution is 14.82 mol/dm3 or 14.82 mol/L

Explanation:

• Molarity is the number of mole present in 1 Litre of solution. Molarity of a solution is a term referred to as concentration of a solution. The unit of Molarity is Mol/dm3 or Mol/L.
• let us make an assumption that the volume of the ammonia solution is 1L or 1dm3. Also, 1L = 1000 mL.

Step 1: calculate the mass of the solution

Density = 0.90g/ml (from the question)

             Density = mass/ volume

Therefore Mass = density x  volume

                          =  0.90g/ml x 1000ml

                mass =  900 g

Step 2: calculate the mass of NH3 present in the solution

Since the concentrated aqueous of ammonia is 28%, It signifies that 1000ml of the solution contains 28% Ammonia

Recall from the above calculation that the mass of 1000 ml of solution is 900 g.

Therefore the mass of ammonia will be 28% of 900 g

                  mass of NH3 = 0.28 x 900 g

                                         = 252 g

Step 3: calculate the number of mole of NH3

        mole = mass/ molar mass

molar mass of NH3 = 17 g/mol

Therefore mole of NH3 = 252/17

                                       = 14.82 mol

Step 4: Calculate Molarity

            Molarity = number of moles/ volume of solution in Litre (L)

            Molarity = 14.82 / 1

            Molarity = 14.82 mol/L