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
