Question

An Aqueous solution is 0.500% by mass ammonia,NH3, and has a density of 0.996g/mL. The molarity of ammonia in the solution is ____M.

Answer 1

Step 1

Molarity is defined as Moles of solute (NH3) divided by the volume of the solution in L

Molarity (mol/L or M) = moles of NH3/volume of the solution (L) (1)

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Step 2

The moles of solute (NH3):

0.500 % by mass means:

0.500 g/100 g solution

Moles of NH3 are calculated as:

Mass of NH3/molar mass NH3 = 0.500 g/17.0 g/mol = 0.029 moles NH3

(molar mass NH3 = 17.0 g/mol)

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Step 2

The volume of solution:

Volume is calculated from density

Density = mass solution/volume of solution

Volume = mass of solution/density = 100 g solution/0.996 g/mL => Volume = 100.4 mL

1L = 1000 mL => V = 100.4 mL = 0.1004 L

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Step 4

From (1)

Molarity = moles of NH3/volume of the solution (L) = 0.029 moles NH3/0.1004 L = 0.289 mol/L

Answer: M = 0.289 M or mol/L