Yr12 A level chem revisions list-mock

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vesq
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Hi, so I received a revision list for my June mock yesterday. The first topic is " % of by mass of an atom". What does he mean, does he mean percentage yield or percentage composition. I don't understand, can anyone help, please.
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Arkcano
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(Original post by vesq)
Hi, so I received a revision list for my June mock yesterday. The first topic is " % of by mass of an atom". What does he mean, does he mean percentage yield or percentage composition. I don't understand, can anyone help, please.
You have a compound CO2 which is carbon dioxide calculate the percentage by mass of Carbon in a 10 gram sample of CO2

so what you do is

(Mr of carbon)/(Mr of CO2)
12/(12+16+16)
= 0.2727..... * 10 grams
this gives us 2.727...... grams
therefore you do
2.7272/10 * 100
therefore the percentage of mass of Carbon is 27.27 or 27.3 % you could do it in fewer steps. I just did it like this so you can understand better.
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