The teacher instructed three students, ‘A’, ‘B’ and ‘C’, respectively, to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of water, while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the desired solution and why?

The answer is student C because both B and A have made the solution of 150 ml, whereas student C prepared the required quantity.

Explanation

Students A and B prepared 150 ml solution, so student c made the desired solution because he added water to make 100 ml solution and from the calculation,

%w/v = 100 × weight of sub (solute) volume of solution

∴ %50 = 100 × weight of sub / 100 ml weight of sub = 50 ×100 ml / 100

∴ weight of sub = 50 g

Here the 50g NaOH required for 50% w/v 100ml solution of NaOH