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Question
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?
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Solution
By definition, 50% mass by volume percent solution means 50 grams of a solute dissolved in 100 mL of solution. Therefore, student C made the desired solution. Student A dissolved 50 g of NaOH in 100 ml of water, So the solution is diluted and is not the desired solution. By definition, 50% mass by mass percent solution means 50 grams of a solute dissolved in 100 grams of solution.
Student B dissolved 50 g of NaOH in 150 g of the solution so, it is not the desired solution.
‘C’ has made the desired solution by dissolving 50 g NaOH in water to make the volume of the solution 100 mL
Mass by volume % = `("Mass of solute")/("Volume of solution") xx 100`
= `50/100 xx 100`
= 50% mass by volume
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