Question

What are the percentage and molar concentrations of a `20*g` mass of common salt dissolved in `80*g` water?

Answer 1

You want the expression, `"moles of solute"/"volume of solution"`..

Explanation:

We ASSUME that `20*g` of salt dissolves in `80*g` of water; and thus our percentage concentration is.....

`(20*g)/(20*g*("salt")+80*g*("water"))xx100%=20%(w_"solute"/w_"solution")`

We FURTHER ASSUME that the volume of the solution is IDENTICAL to (or close enuff) to `80*mL`....

And this for molar concentration we take as usual the quotient......

`"Moles of stuff"/"Volume of solution"=((20*g)/(58.44*g*mol^-1))/(80xx10^-3*L)~=4*mol*L^-1`