Asked by shirley

If you start with 1.200 g of BaCl2 X(multiplied) 2H20 and heat if for 4-8 min, what will be the mass of the water removed?
Answered by DrBob222
Moles BaCl2.2H2O = grams/molar mass
moles BaCl2.2H2O x (2 moles H2O/1 mole BaCl2.2H2O) = moles BaCl2.2H2O x 2/1 = ??
mass H2O = moles H2O x molar mass H2O
Post your work if you get stuck.
Answered by shirley
so would i take the mass of BaCl2 which is 207 and then divide it by the molar mass of 1.200 to get 172? I'm not sure that it's right.
Answered by DrBob222
No. You want the molar mass of BaCl2.2H2O since that's the material that has a mass of 1.2 grams. I think its 244 something.
Answered by shirley
so i found the molar mass of BaCl2.2H20 to be to be 207. but when i divided that by 1.200 i got 172.5. how did you get the value 244?
Answered by shirley
i multiplied 207 by 1.200 to get 248.4, was that the value that you meant by being close to 244?
Answered by DrBob222
No. The molar mass of BaCl2.2H2O is
Ba = 137.327
Cl = 35.453 x 2 = 70.9054
H2O = 18.015 x 2 = 36.0306
total = 244.263 for BaCl2.2H2O.
1.2/244.263 = 0.00491 moles BaCl2.2H2O

moles H2O evolved = 0.00491 x (2 moles H2O/1 mole BaCl2.2H2O) = 0.00491 x 2 = 0.00983 moles H2O.

grams H2O = moles x molar mass = 0.00983 x 18.015 = 0.17701 grams which I would round to 0.18 grams (to two significant figures since 1.2 has two).
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