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    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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    This chemistry teacher, is one of the best guys I know. He goes through so many topics so clearly and well!! I use him to study when I get stuck too, I am on the same topics as you and I watch this guy to help me understand!

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    (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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