Grade 11 Chemistry Concentration Problems/Solutions

Concentration Problems

1. What mass of NaCl is needed to produce a 500 g of a 6.40% M/M solution?


% M/M = ( M[solute] ÷ M[solution] ) x 100


M[NaCl] = ( 6.4 x 500 ) ÷ 100
= 32 g


∴ 32 g of NaCl is needed.


2. What is the concentration, in g/100 mL, of a solution made by dissolving 123.2 g
of phosphoric acid in 50.0 mL of solution?


C = quantity ÷ volume
= 123.2 g ÷ 50 mL
= 2.464 g/mL


100 𝑚𝐿
2.264 g/ml x = 246.4 g/100mL
100 𝑚𝐿



∴ 246.4 g/100mL is the concentration.


3. How much water is needed to produce a 0.68 M solution of copper (I) carbonate,
if 3.58 g is used?

, MM [Cu₂CO₃] = ( 63.546 x 2) + 12.011 + ( 15.999 x 3 ) = 187.1 g/mol


Moles to grams:
3.58 g ÷ 187.1 g/mol = 0.019 mol Cu₂CO₃


Molarity = moles ÷ L
L = 0.019 mol ÷ 0.68 M
= 0.028 L


∴ 0.028 L or 28 mL water is needed.


4. What mass of carbon dioxide would you add to 1 500 L of water in order to make
a 325 ppm solution?



C = ( quantity ÷ volume ) x 10⁶ ppm


Quantity = ( 325 ppm x 1500000 g ) ÷ 10⁶
= 487.5 g


∴ 487.5 g of carbon dioxide is needed.



5. What is the concentration of a solution made by diluting 14.0 mL of a 4.20 M
Na₂CO₃ to 86.0 mL?


CᵢVᵢ = CfVf