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# A2 Percentage yield question- help required : ) watch

1. A student made 1.10g of dipeptide H starting from 1.40g of glycine.
Calculate the percentage yield (%) obtained. Give your answer to 3 sig. figs.

Thanks loads to anyone who can help me; I've always had trouble with percentage yields....
2. (Original post by play_the_world)
A student made 1.10g of dipeptide H starting from 1.40g of glycine.
Calculate the percentage yield (%) obtained. Give your answer to 3 sig. figs.

Thanks loads to anyone who can help me; I've always had trouble with percentage yields....
What is there here not to understand?!

Percentage yield = End Product / Starting Product x 100

1.1 / 1.4 x 100 = 78.6%

In this reaction...

2 x glycine --> dipeptide + H20

since the dipeptide is formed by a condensation reaction the remaining 21.4% is due to the water produced
3. Well I thought it would be more complicated than that, because the question is worth 4 marks. Thanks alot anyway.
4. Actually, I think what you're looking for is:

% yield = [actual yield (in grams) / predicted yield (in grams) ] x 100

To work out the predicted yield you'd have to do some moles calculations using the equation for the reaction ... which would probably be why it's worth 4 marks.

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Updated: November 17, 2005
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