What is the Molarity, %(w/v), and parts per million(ppm) of the solution?

Question

A solution prepared by mixing 50g of sodium carbonate into a total solution volume of 500 ml

Answer 1

molarity =moles/V where volume is expressed in L.
moles=mass/MW so

molarity=mass/(MW*V) =50/(106*0.5)= 0.94 M

For solutions, % (w/v) is grams of solute per 100 mL of solution.
Thus you have (50/500)*100% = 10%

% is parts per hundred.
so it is 10^4 times bigger than ppm
so it is 10*10^4 ppm= 10^5 ppm.
1 ppm corresponds to 1 mg of solute per 1L of solution.

Answer 2

Molarity: figure out how many moles 50 g of sodium carbonate is and divide by 0.5 because molarity is moles per liter and 500 ml is half a liter.

% (w/v): This notation means percent with respect to weight to volume. So, you have 50 grams going into 500 ml. So, divide the two. You should give this some thought. Why do you divide by 500 ml and not 0.5 liter? Hint: what does percent mean?

ppm: parts per million and this usually means weight-to-weight. Here you have to assume that the solvent is water and the total solution weighs 500 grams. The easiest way is to make one unit or the other one million times the other. Given that you have 50 g going into 500 g, I would restate 50 g as micrograms. Figure out how many micrograms are in 50 grams, divide by 500 grams and you have parts per million.

Good luck.