question_answer 40)

  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?

Answer:

  In the given question, student 'C' has made it correctly because 50% (mass by volume) means 50 g of solute for every 100 mL of solution and not in 100 mL of solvent. Mass/volume per cent Student 'A' dissolved 50 g of NaOH in 100 mL  of water (solvent) which is incorrect. Student 'B' dissolved 50 g of NaOH in 100 g of water (solvent), which is incorrect.