Question

In the course of doing valuable biomedical research one day, let's say you make a salt solution by adding 1 mol of NaCl to 90 g of water. 

What is the percent by mass (i.e. mass %) of the solution? 

Answer 1

Mass of 1 mol of NaCl:

$m=\nu\cdot M=1mol\cdot58.5g/mol=58.5g - NaCl$

Total mass: $m_0=58.5g+90g=148.5g$

Mass % of NaCl: $58.5g/148.5g\cdot 100$ %$=39.39$ %

Mass % of water: $(100-39.39)$ %$=60.61$ %