Concentration of a solution: Class 9 practice
Mass percent = mass of solute ÷ mass of solution × 100, where solution = solute + solvent. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Percentages
The idea behind concentration of a solution
Mass percent = mass of solute ÷ mass of solution × 100, where solution = solute + solvent. For very dilute solutions, ppm = mass of solute ÷ mass of solution × 10⁶.
Step-by-step method
- Add solute and solvent to get the solution mass.
- Divide the solute mass by the solution mass.
- Multiply by 100 (percent) or 10⁶ (ppm).
Worked example 1 (Basic)
45 g of salt is dissolved in 103 g of water. Find the mass percent.
- Solution = 148 g
- 45 ÷ 148 × 100
- Answer: 30.41%
Worked example 2 (Standard)
How much sugar is needed for 400 g of a 25% (by mass) solution, and how much water?
- Sugar = 25% × 400 = 100 g
- Water = 300 g
- Answer: 100 g sugar, 300 g water
Worked example 3 (Challenge)
39 mg of fluoride is in 1 kg of water. Express this in ppm.
- 39 mg ÷ 1000000 mg × 10⁶
- Answer: 39 ppm
Common mistakes and misconceptions
- Dividing by the solvent mass
- Using 1000 for ppm
Practice questions
- (Basic) 5 g of salt is dissolved in 53 g of water. Find the mass percent.
- (Basic) 9 g of salt is dissolved in 104 g of water. Find the mass percent.
- (Standard) How much sugar is needed for 300 g of a 20% (by mass) solution, and how much water?
- (Standard) How much sugar is needed for 900 g of a 12% (by mass) solution, and how much water?
- (Challenge) 31 mg of fluoride is in 1 kg of water. Express this in ppm.
- (Challenge) 27 mg of fluoride is in 5 kg of water. Express this in ppm.
Answer key with full working
- Q1: Solution = 58 g → 5 ÷ 58 × 100 → Answer: 8.62%
- Q2: Solution = 113 g → 9 ÷ 113 × 100 → Answer: 7.96%
- Q3: Sugar = 20% × 300 = 60 g → Water = 240 g → Answer: 60 g sugar, 240 g water
- Q4: Sugar = 12% × 900 = 108 g → Water = 792 g → Answer: 108 g sugar, 792 g water
- Q5: 31 mg ÷ 1000000 mg × 10⁶ → Answer: 31 ppm
- Q6: 27 mg ÷ 5000000 mg × 10⁶ → Answer: 5.4 ppm
Syllabus note
This skill is listed under "Is Matter Around Us Pure" for Class 9 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is concentration of a solution in?
"Is Matter Around Us Pure", Class 9 Chemistry (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.