AS chemistry
A compound which contains carbon and hydrogen only, 0.2801 g of which gave 0.9482 g of carbon dioxide on
complete combustion. Calculate the empirical formula of this compound.
complete combustion. Calculate the empirical formula of this compound.
This website has a good step-by-step guide for these questions: https://study.com/skill/learn/determining-an-empirical-formula-from-combustion-data-explanation.html
Does the question also provide mass of water produced?
Does the question also provide mass of water produced?
No, it doesn't provide a mass of water. That's all I've been given.
Original post by neha_issac
A compound which contains carbon and hydrogen only, 0.2801 g of which gave 0.9482 g of carbon dioxide on
complete combustion. Calculate the empirical formula of this compound.
complete combustion. Calculate the empirical formula of this compound.
Where did you find this question?
Whilst they should have given you the amount of water produced, it isn’t impossible to answer the question, but the method I think should work is rather ugly and I doubt it’d be expected for an exam.
Start by finding the moles of CO2 produced.
It's from this worksheet I got given as homework in class. I found the moles of CO2 but don't know where to go from there without the water. This is the question: https://tinypic.host/image/0ibyh
(edited 3 months ago)
Original post by neha_issac
It's from this worksheet I got given as homework in class. I found the moles of CO2 but don't know where to go from there without the water.
That's the question: https://tinypic.host/image/0ibyh
The moles of CO2 = the moles of carbon in the hydrocarbon.
Given the Ar of carbon is 12 g/mol, what is the mass of carbon contained within the compound?
Given the Ar of carbon is 12 g/mol, what is the mass of carbon contained within the compound?
Is it 0.9482/44 which is the moles of CO2 which equals 0.02155mol. Then multiply 0.02155 by 12 to get the mass of carbon which is 0.2586g.
Original post by neha_issac
Is it 0.9482/44 which is the moles of CO2 which equals 0.02155mol. Then multiply 0.02155 by 12 to get the mass of carbon which is 0.2586g.
They told you the mass of compound was 0.2801 g and it is made up only of carbon and hydrogen.
Following on from finding the mass of carbon in the compound, how much hydrogen must there be?
0.2801-0.2586g=0.0215g of hydrogen
Original post by neha_issac
0.2801-0.2586g=0.0215g of hydrogen
So how many moles of hydrogen is that?
You already know there are 0.02155 mol of carbon and so, what is the ratio of C : H?
Is the ratio 0.02155:0.0215?
Original post by neha_issac
Is the ratio 0.02155:0.0215?
Try dividing both sides of the ratio through by 0.0215 (the smallest part of the ratio) and see what the ratio roughly turns out to be
Is it roughly 1:1 so the empirical formula is CH
Original post by neha_issac
Is it roughly 1:1 so the empirical formula is CH
That is correct
thank you so much. I have one question. How did you know that’s the moles of Carbon dioxide and the moles of carbon were the same?
Original post by neha_issac
thank you so much. I have one question. How did you know that’s the moles of Carbon dioxide and the moles of carbon were the same?
You can thank a friend of mine for this particular solution as my original method was much more complicated.
Because you are completely combusting the hydrocarbon, all of the carbon atoms in the hydrocarbon are being converted to CO2. Each CO2 molecule contains 1 carbon, so each mole of CO2 burned must contain one mole of carbon atoms that originally came from the hydrocarbon.
Original post by TypicalNerd
You can thank a friend of mine for this particular solution as my original method was much more complicated.
Because you are completely combusting the hydrocarbon, all of the carbon atoms in the hydrocarbon are being converted to CO2. Each CO2 molecule contains 1 carbon, so each mole of CO2 burned must contain one mole of carbon atoms that originally came from the hydrocarbon.
Because you are completely combusting the hydrocarbon, all of the carbon atoms in the hydrocarbon are being converted to CO2. Each CO2 molecule contains 1 carbon, so each mole of CO2 burned must contain one mole of carbon atoms that originally came from the hydrocarbon.
Ok, I understand, thank you.
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