Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Tezz on August 25, 2020, 07:34:55 AM
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Hi all, when I do this question I get a percentage yield above 100% which makes me question whether I am right. Could someone check it over? Thanks
I currently have an answer of 116.86%
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Can you show your working? 10 lines of text shouldn't be that large to type out (which will also help searches in the future, in case the image breaks)
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1/28.1 = 0.035587... mols
Molecular mass of SiCl4 = 28.1+4(35.5)
=170.1
0.035587 x 170.1 = 6.05338g
6.05338/3.5 = 1.729537 g/cm^3
1.729537/1.48 = 1.1686
Therefore, 116.86%
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You got it reversed.
(not that it makes much sense comparing density with hypothetical density of the product, calculate mass of the product from the data given)
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Ah, I thought I might have done that. So it should be 1.48/the other value?
I thought that 1.48 was the theoretical yield of the reaction
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1.48g/ml is the density of the product.
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1.48g/ml is the density of the product.
Alright thanks, I’ll go and modify my answer to whatever 1.48/other density comes out as. Appreciate the help
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Alright thanks, I’ll go and modify my answer to whatever 1.48/other density comes out as. Appreciate the help
You do understand it doesn't make physical sense (even if it produces a correct number)?
Density is not something that can randomly change, for a given substance (and PT) it is always the same.
What matters here is not the density, but mass of the product.
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1.48g/ml is the density of the product.
Alright thanks, I’ll go and modify my answer to whatever 1.48/other density comes out as. Appreciate the help
NO there is no other density in the question and you can not calculate a density of anything from the information given.
The correct way to solve the problem is:
- Write out the balanced equation for the reaction and determine how many moles of product are formed per mole of starting material in this case it is 1:1 but in other cases it will be different.
- Calculate how many moles of starting material were used.
- Calculate how man moles of product were formed (for this you'll need to calculate the weight of product from the volume and density given)
- Divide the moles of product formed by the moles of starting material used to give the % yield (if from the reaction equation they are not in a 1:1 ratio you need to account for that at this stage.
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I recommend to write the units each and every time you make a computation, and double-check their consistency.
Secret: professional scientists don't memorize formulas. They compute according to the units.