Chem.Question.(Uni 1st year)

Question

'you have been asked to make up 920 ml of a 33.3% (w/v) solution. How many grams of the compound would you need (to 2 dp)?'

33.3% w/v is it mean 33.3g of A made up to 100mL ?

And whats the method to do this? (no need to write the numerical answer, just use algebras)

更新:

AND ALSO:

Qn2: If you dissolved 95.83 g of a compound in water and made it up to a final volume of 370 ml, what would be the percentage weight by volume (w/v) concentration of the solution (to 2 dp)?

Thanks!!

Answer 1

最愛解答

yes, for w/v (weight-to-volume), you directly divide the mass (in g) by volume (in ml).

of course in the unit like g/ml, they aren't canceling each other, but that's just some convention showing the proportions of solutes in solutions.

other than w/v, there're also w/w and v/v.

w/w : mass of solute / mass of solution, typically used in concentrations of solids and liquids w/v : mass of solute / volume of solution, typically used in concentrations of liquids v/v : volume of solute / volume of solution, typically used in concentrations of liquids and gases

and answer for second question is 25.90%, assuming volume of water doesn't change after dissolution of such a large amount of solid.