Chemistry Help, empirical and molecular formula

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Frozetman
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An organic compound X, which contains Carbon, Hydrogen and Oxygen only has a Molar mass of 85

When 0.43g of X are burned in excess oxygen, 1.10g of Carbon Dioxide and 0.45g of Water are formed.

Find the empirical and molecular formulae of compound X

Pls help i rlly don't understand what I'm doing here
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Gabriel-01
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So, you need to find the number of moles of CO2 and H2O. This gives you the moles of C and H in the compound X. Then add these values together and minus from the number of moles of compound X, this will give you the moles of oxygen. Then when you have all these values, divide each one by the smallest and that will give you the empirical formula. To find the molecular formula, divide the Mr of compound X by each of the values in the ratio and this gives you the true number of atoms of each element in the compound.

Hope this helps or makes sense/is correct…been awhile since I did a level chem 😬
Last edited by Gabriel-01; 4 weeks ago
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5hyl33n
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(Original post by Frozetman)
An organic compound X, which contains Carbon, Hydrogen and Oxygen only has a Molar mass of 85

When 0.43g of X are burned in excess oxygen, 1.10g of Carbon Dioxide and 0.45g of Water are formed.

Find the empirical and molecular formulae of compound X

Pls help i rlly don't understand what I'm doing here
Step 1:
Find the mass of carbon using the mass of carbon dioxide.
Hint: First use the equation Moles = mass / Mr to find the number of moles in carbon dioxide. Multiply this answer by 12 (Mr of carbon) to find the number of moles in just carbon.

Step 2:
Find the mass of hydrogen using the mass of water.
Hint: First use the equation Moles = mass / Mr to find the number of moles in water. Multiply this answer by 2 (Mr of hydrogen) to find the number of moles in just hydrogen.

Step 3:
Find the mass of oxygen.
Hint: Add the masses of hydrogen + carbon. Subtract from the total mass of X.


Can you carry on and find the empirical and molecular formula given you now have the mass of carbon, hydrogen and oxygen?
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Frozetman
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Thanks for the help,

I've gotten the empirical formula as C5H10O6 using this method but the Molar mass adds up to be more than 85 (12x5 = 60 + 10x1 = 70 + 16 = 86)

Could it just be that the question made an error in the figures or have I done something wrong?
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5hyl33n
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(Original post by Frozetman)
Thanks for the help,

I've gotten the empirical formula as C5H10O6 using this method but the Molar mass adds up to be more than 85 (12x5 = 60 + 10x1 = 70 + 16 = 86)

Could it just be that the question made an error in the figures or have I done something wrong?
Can you post your working out? I think you have gone wrong somewhere.
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5hyl33n
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(Original post by Frozetman)
Thanks for the help,

I've gotten the empirical formula as C5H10O6 using this method but the Molar mass adds up to be more than 85 (12x5 = 60 + 10x1 = 70 + 16 = 86)

Could it just be that the question made an error in the figures or have I done something wrong?
https://www.thestudentroom.co.uk/sho...d.php?t=687079

Look at this thread. It gives a perfect explanation of what the answer is. You are very close to the answer!
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Frozetman
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Thanks soo much I’ve looked at the thread and I understand how to answer it now
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