# chem moles help

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#1
A student was given a powder made from a mixture of anhydrous barium
chloride and anhydrous magnesium chloride. The student dissolved 1.056 g of
the powder in water in a conical flask and added an excess of sulfuric acid.
A white precipitate formed and was filtered off, washed and dried.
The mass of this solid was 0.764 g.
Identify the white precipitate and calculate the percentage, by mass, of
magnesium chloride in the powder.
0
8 months ago
#2
Edit :
So we've got BaCl2, MgCl2 and H2SO4
If you've revised thru solubility rules, which of these would react to give white precipitate?
Lets imagine if theres A, B, C and lets say A and B reacted to give D. Whats remaining? C right? Question asks us to find percentage of C present...try to guess how...
Last edited by gongoozled goose; 8 months ago
0
8 months ago
#3
I'm sorry i wrote out wrong, i edited now
Ok so we've got MgCl2 and BaCl2 reacting w/ sulfuric acid.. what do we get?
0
8 months ago
#4
Right! now which of them would be soluble and insoluble? This insoluble precipitates's mass is 0.764g frm the question.
0
8 months ago
#5
Yep so now using the balanced equation you would know the moles of BaCl2 that reacted with H2SO4
Be reminded of the fact that 1.056g in the question is the total mass of BaCl2 and MgCl2
Last edited by gongoozled goose; 8 months ago
1
8 months ago
#6
barium sulfate is insoluble, but magnesium sulfate is soluble, so only barium sulfate is the white precipitate. Use the Mr of barium sulfate and the mass of the precipitate (barium sulfate) to figure out moles of barium sulfate. This will be same as the original moles of Barium chloride. So use moles of original Barium chloride and Mr of barium chloride to calculate the mass of barium chloride. Take this away from the total mass of powder which reacted (1.056g) to find the mass of Magnesium chloride in the powder. Then just do (mass of magnesium chloride) divided by (total mass of powder), and then multiply by 100 to find the % mass of magnesium chloride in the powder.

I just did the question using my above logic and got 36.6 % but did some rounding so could be a tad off, could you please tell me if this is around the right answer?
2
8 months ago
#7
great, thanks

won't let me rep cus i've repped you recently :/
0
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