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 $\mathrm{NaOH}$ in 100 mL of water,'B' dissolved 50g of $\mathrm{NaOH}$ in 100g of water while'C' dissolved 50g of $\mathrm{NaOH}$ in water to make mL of solution. Which one of them has made the desired solution?

Answer 1

Student C makes the desired solution because he adds water to produce a 100 ml solution after Students A and B prepare a 150 ml solution.

$\begin{array}{rcl}\mathrm{Mass}\mathrm{by}\mathrm{volume}\%& =& \frac{\mathrm{Mass}\mathrm{of}\mathrm{solute}}{\mathrm{Volume}\mathrm{of}\mathrm{solution}}\times 100\\ & =& \frac{50}{100}\times 100\\ & =& 50\%\mathrm{mass}\mathrm{by}\mathrm{volume}\end{array}$

50g of NaOH are dissolved in 100ml of solution, or 50% mass by volume. C, therefore, creates the answer.

A has already consumed 100 ml of water and makes 150 ml of solution. As a result, A fails to provide the anticipated outcome.

B consumed 100 grams of water also makes 150 g of solution. Therefore, the solution won't be 50% mass by volume for either A or B.