Multiple choice

A container contains 10 litres mixture in which there is 10 \% sulphuric acid. How much sulphuric acid is to be added to make the solution to contain 25 \% sulphuric acid ?

  1. 1 litre

  2. 2 litre

  3. 3.5 litre

  4. 2.5 litre

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initial mixture: 10 litres with 10% acid = 1 litre acid, 9 litres other. Let x litres of pure acid be added. New volume = 10 + x litres. New acid = 1 + x litres. We need 25% acid: (1 + x)/(10 + x) = 25/100 = 1/4. Cross-multiplying: 4(1 + x) = 10 + x. 4 + 4x = 10 + x. 3x = 6. x = 2 litres.