Problem 56 - Chemistry The Central Science

Question

Commercial concentrated aqueous ammonia is \(28 \% \mathrm{NH}_{3}\) by mass and has a density of \(0.90 \mathrm{~g} / \mathrm{mL}\). What is the molarity of this solution?

Step-by-Step Solution

Answer

The molarity of the concentrated aqueous ammonia solution is \(14.8 \mathrm{M}\).

Step 1: Calculate the mass of ammonia in 1 L of solution

To determine the mass of ammonia in 1 L of the solution, we need to use the mass percentage (28%) and the density (0.90 g/mL) of the solution. First, find the mass of the 1 L solution by multiplying its density with the volume: Mass of 1 L solution = Density × Volume Mass of 1 L solution = 0.90 g/mL × 1000 mL Mass of 1 L solution = 900 g Next, multiply the mass of the 1 L solution by the mass percentage to find the mass of ammonia: Mass of ammonia = Mass of 1 L solution × mass percentage Mass of ammonia = 900 g × 0.28 Mass of ammonia = 252 g

Step 2: Calculate the number of moles of ammonia

Now that we have the mass of ammonia, we can find the number of moles of ammonia by dividing the mass by the molar mass of ammonia (NH3). The molar mass of ammonia is: Molar mass of ammonia = 14.01 g/mol (N) + 3 × 1.01 g/mol (H) = 17.03 g/mol Now, divide the mass of ammonia by its molar mass to find the moles: Moles of ammonia = mass / molar mass Moles of ammonia = 252 g / 17.03 g/mol Moles of ammonia = 14.8 mol

Step 3: Calculate the molarity of the solution

Finally, we can calculate the molarity of the solution by dividing the moles of ammonia by the volume of the solution in liters: Molarity = moles / volume Molarity = 14.8 mol / 1 L Molarity = 14.8 M The molarity of the concentrated aqueous ammonia solution is 14.8 M.