chem amount to mass (1 Viewer)

[Dumdida]

i have a problem, saying 0.1428g of calcium bromide was dissolved in 950mL water, find the concentration of bromide ions in ppm. I derrived the chemical amount of bromide ions which is 0.001429 mol
now it says convert this chem amount to mass (mg), then divide the mass by the volume (950mL). The thing is i cannot derrive the mass, the answer states that the mass is 114.2 mg, anybody know how to get this amount?

 

[tam89]

n(Br ions)= 0.001429 mol

mass(Br ions) = chemical amount Br ions X molar mass of Br ions
= 0.001429 x 79.90
= 0.1142 g
= 114.2mg #

 

[Jumbo Cactuar]

For anyone who cares:

ppm (parts per million) is a unit of molality (not molarity). It is used extensively in environmental studies. ie copper content in water etc. Also, consumer goods normally quote molality of active ingredients.ie toothpaste active ingredients: NaF 0.22 w/w%. It's used lots more places as well.

What I am getting at is it useful to know as well as imperitive for some of us and sometimes an eyeopener (with regards to consumer goods).

molality = (weight of solute/ weight of solvent) * 10^6 ppm
m = (weight of solute/ (density of solvent * volume of solvent)) * 10^6 ppm

for aqueous measurements:
density of solvent = 10^3 g/L
hence;
m = (weight of solute / volume of solvent) * 10^3 ppm
and
m = (concentration of solute * molar mass of solute) * 10^3 ppm

and ppb = ppm * 10^3.