Chapter 4 Concentration of Solutions MCQ 2

Concentration of Solutions

• Concentration is the amount of solute in a specified amount of solution.
• It can be expressed as moles per liter (M), grams per liter (g/L), and parts per million (ppm).

Converting between Concentration Units

• To convert g/L to M, divide by the molar mass (Mr).
• To convert g/L to ppm, multiply by 1000.
• To convert M to g/L, multiply by the molar mass (Mr).
• To convert ppm to g/L, divide by 1000.

Calculating Concentration

• To calculate the concentration of a solution, you need to know the amount of solute and the volume of the solution.
• Example: 1g of copper sulfate (CuSO₄) in 100mls of water has a concentration of 10g/L.

Expressing Concentration in Different Units

• Example: 0.006 M NaOH solution is equivalent to 0.24g/L and 240ppm.
• Example: 74ppm solution of HCl is equivalent to 0.074g/L and 0.002 M.

Calculating Mass of Solute

• To calculate the mass of solute, you need to know the volume, concentration, and molar mass of the solute.
• Example: 500cm³ of 0.02 M KOH solution contains 5.6g of KOH.

Calculating Moles of Solute

• To calculate the moles of solute, you need to know the volume and concentration of the solution.
• Example: 100cm³ of 0.1M hydrochloric acid solution contains 0.01 moles of HCl.

Concentration Involving Percentages

• 5% w/v means 5g of solute in 100mls of solvent.
• 6% v/v means 6mls of solute in 100mls of solvent.
• 11% w/w means 11g of solute in 100g of solvent.

Calculating Percentage Concentration

• Example: 2.125g of salt (NaCl) in 250mls of water has a concentration of 0.85% w/v.
• Example: A 500mls bottle of beer containing 25mls of pure alcohol has a concentration of 5% v/v.
• Example: 40g of a solution containing 5g of solute has a concentration of 12.5% w/w.