Formulae:
Molarity, M = # moles of solute / Liters of solution
# moles = grams / molar mass
Reaction:
\(Ba Br_{2} -\ \textgreater \ Ba^{+2} +2 Br^{-}\)
1) BaBr2
molar mass = 137.33 + 279.90 = 297.13 g/mol
# moles = grams / molar mass = 2.3710^-4 g / 297.13 g/mol = 7.9810^-7 moles
Liters of solution: in this case the volumen is that of the water because the volume of the solute is negligible.
M = 7.98 10^-7 mol / 1 L = 7.98 10^-7 M
2) Ba+2
The chemical reaction tells that the molar ratio of Ba+2 ions to BaBr2 is 1:1, then that same proportion remains for the molarity and you have
M = 7.98 10^-7 M
3) Br -
The chemical reaction shows that the molar ratio of Br- ions to BaBr2 is 2:1, then the Molarity will be also 2:1
M = 27.98 10^-7 M = 1.6010^-6 M
ppm
To find ppm concetration of the ions first determine their weight divide by the mass of solution and multiply by 10^6
Ba+2 mass = # of moles molar mass = 7.9810^-7 mol 137.33 g/mol = 0.00011 g
ppm = [0.00011g/1000 g of solution] 1000000 = 0.11 ppm
(note that I didn't add the 0.00011 g to the mass of the solution because 0.00011 is negligible in front of 1000 g)
Br - mass = 2 7.9810^-7 mol 79.90 g/mol = 0.00013 g
ppm = 0.00013 * 1000000 / 1000 = 0.13 ppm
