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The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50\% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50 g of NaOH in 100 mL of water, ‘B’ dissolved 50 g of NaOH in 100 g of water while ‘C’ dissolved 50 g 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:
Mass by volume:  X% mass by volume solution means X grams of a solute dissolved in 100 mL of solution.
Mass by volume (\%)=\frac{mass\; of\; solute \times100}{Volume\; of\; solution}
Student A:  dissolved 50 g of NaOH in 100 mL of water.
Therefore, volume of solution will be more than 100 ml as only solvent is 100 mL.
This solution will have less than 50\% (mass by volume) solution
Student B:  dissolved 50 g of NaOH in 100 g of water.  (100 gram water =100mL of water)
Therefore, volume of solution will be more than 100 ml as only solvent is 100 mL.
This solution will have less than 50\% (mass by volume) solution.

Student C:  dissolved 50 g of NaOH in water to make 100 mL.
It means, Volume of solution is 100mL.
C has made the desired solution by dissolving 50 g NaOH in water to make the volume of the solution 100 mL

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