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# Chemistry Homework Question watch

1. Calculate the mass of:
(a) calcium chloride, CaCl2, required to make 100 cm^3 of a solution, concentration 2.0 mol dm^-3.
(b) pure sulfuric acid, H2SO4, required to make 0.500 dm^3 of a solution, concentration 5.0 mol dm^-3.
(c) sodium chloride, NaCl, required to make 200 cm^3 of a solution, concentration 0.50 mol dm^-3.

I know how to do concentration but when i came across this question about mass I was totally confused. Any help is appreciated.
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Hope this helps!!
3. (Original post by Want_To_Achieve)
Calculate the mass of:
(a) calcium chloride, CaCl2, required to make 100 cm^3 of a solution, concentration 2.0 mol dm^-3.
(b) pure sulfuric acid, H2SO4, required to make 0.500 dm^3 of a solution, concentration 5.0 mol dm^-3.
(c) sodium chloride, NaCl, required to make 200 cm^3 of a solution, concentration 0.50 mol dm^-3.

I know how to do concentration but when i came across this question about mass I was totally confused. Any help is appreciated.
Right, I think that what the question is really getting at is moles.

So, for each question, the number of moles calculated using moles=mass x Mr must equal the number of moles calculated using moles= concentration x volume because no equations have been given, so you just have to use the numbers

I'll do the first one as an example.

moles = concentration x volume = 2.0 x 100/1000 = 0.2mol
mass = molesx Mr = 0.2 x (40.1 x 2 + 35.5 x 2) = 22.22g = 22.2g (3sf)

then just do that for the other two.

hope that helps

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