You are Here: Home

# Blagh, more issues~ watch

1. Ethene (C2H4) and steam react to form ethanol (C2H6O).

C2H4  +  H2O  →  C2H6O

What mass of ethanol is formed from 14 g of ethene?
(Relative atomic mass: H = 1; C = 12; O = 16)

Super confused here, I'd love some help. ;3
2. You first need to find the number of moles of ethene in 14 g, found by moles = mass / RMM.

You know that one molecule of ethene will form one molecule of ethanol (1 : 1 mole ratio), so the the number of moles of ethene used will be the same as the number of moles of ethanol formed.

Then you find the mass of ethanol with mass = moles x RMM.

Try and work it out and I'll tell you if you got it right.
3. Ick, I'm still confused

I managed to work out that the relative mass of ethene is 28.
Ethanol is 42.

I'm confused on what RMM means.

(I apologise for the negative reputation thing! I didn't realise it was on that until I had pressed enter and by then it was too late, I think! I'll re-rep you tomorrow. <3)
4. RMM = Relative Molecular Mass.

ie: Sum of the the relative atomic masses of the atoms in a molecule

Anyways, back to the problem.

Divide the mass of ethene (14g) by its relative molecular mass to get the NUMBER OF MOLES OF ETHENE REACTING.

If you look at the chemical equation, 1 mole of Ethene reacts to form one mole of Ethanol. So the number of moles of ethanol you get is equal to the number of moles of ethene you have at the start.

to get the mass of ethanol formed, you use the formula MASS = MOLES X RELATIVE MOLECULAR MASS.

I hope that makes sense
5. RMM = relative atomic mass which is what you've worked out. Try finding the RMM of ethanol again. It's actually 46 g/mol. I know it was probably a silly error. I'll take you through the question.

You have 14 g of ethene. In moles this would be:

moles = mass / RMM

= 14 / 28

= 0.5 mol

Because one molecule of ethene forms one molecule of ethanol, 0.5 moles of ethene forms 0.5 moles of ethanol.

(You know this from the equation C2H4  +  H2O  →  C2H6O. For a different example, in O2 + 2 H2 → 2 H2O, one oxygen molecule would form two molecules of water so you would have to double the number of moles for this case.)

You now know you form 0.5 moles of ethanol. You now convert this into a mass:

mass = moles x RMM

= 0.5 x 46

= 23 g
6. Oh, crud! No wonder why I'm getting it wrong! O__O;
Thank you!
7. you're diving the RMM by the mass. Moles is the mass divided by RMM i.e. 28 / 14.

Once you have the moles of ethanol, multiply that by the RMM of ethanol, not ethene.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: January 17, 2010
Today on TSR

### He broke up with me because of long distance

Now I'm moving to his city

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University