question_answer

Which of the following options does not represent concentration of semi- molal aqueous solution of NaOH having \[{{d}_{solution}}=1.02g/mL\]?

A)  Molarity\[=\frac{1}{2}M\]

B) \[{{x}_{NaOH}}=\frac{9}{1009}\]

C) \[%w/w=10%\]

D) \[%\,w/v=2%\]

Correct Answer: C

Solution :

[c] : Semi-molal \[\Rightarrow \frac{1}{2}m\]or mol \[\text{k}{{\text{g}}^{-1}}\] \[d=1.02g/mL\] 1 kg of water contains\[\frac{1}{2}\]mole of NaOH i.e., 20 g Mass of solution \[=1000+20=1020g\] Volume of solution \[=\frac{1020}{1.02}=1000\,\text{mL}=1\,\text{L}\] \[%w/w=\frac{20}{1020}\times 100=2%\] \[%w/v=\frac{20}{1000}\times 100=2%\]