You are Here: Home >< GCSEs

# Percentage yield HELP!!! watch

1. (Original post by Dylann)
waiting to use percentage yield now like the title suggests...!

The coefficient never tells you how many moles are actually there, but rather the RATIO in which it reacts with other reactants.

2x + 5y ---> 3z + 4w

This means that every 2 moles of x react with 5 moles of y producing 3 moles of z and 4 moles of w

It doesn't tell you how many moles of each substance you actually have...just the RATIO in which they react...very important you don't get confused...
Ohh okk thanks once again
What board r u doing for science???
2. (Original post by Fallen99)
Ohh okk thanks once again
What board r u doing for science???
I'm an A2 student doing AQA
3. (Original post by Dylann)
I'm an A2 student doing AQA
Ohh that is why u r soo good at chemistry just one more question
You said we can add the masses together but can we workout the moles for each compound and add them together??
4. (Original post by Fallen99)
Ohh that is why u r soo good at chemistry just one more question
You said we can add the masses together but can we workout the moles for each compound and add them together??
I didn't realise the equation wasn't balanced not that good haha!

You shouldn't add the masses together...you should work out the moles of each reactant individually and see which is in excess
5. (Original post by Dylann)
I didn't realise the equation wasn't balanced not that good haha!

You shouldn't add the masses together...you should work out the moles of each reactant individually and see which is in excess
I didn't realize that too.
I get that we can work out the moles of reactants individually but what do u mean by which is in excess??
6. its just outcome yield divided by actual yield and time by 100. It's the easiest calculation i think in c2. gl.
7. (Original post by Fallen99)
I didn't realize that too.
I get that we can work out the moles of reactants individually but what do u mean by which is in excess??
If there are 2 moles of X and 3 moles of Y and they react in a 1:1 ratio then Y is in excess...i.e. when all of X is used up there is still some Y left over.
8. (Original post by Dylann)
If there are 2 moles of X and 3 moles of Y and they react in a 1:1 ratio then Y is in excess...i.e. when all of X is used up there is still some Y left over.
Thanks a lot do u mind if I look out for u on tsr if I need help in chemistry in the future??
9. (Original post by Fallen99)
Thanks a lot do u mind if I look out for u on tsr if I need help in chemistry in the future??
Yeah just PM me
10. (Original post by Dylann)
Yeah just PM me
Thanks

Posted from TSR Mobile
11. (Original post by Dylann)
mol=Mass in grams/Mr

Mr = Relative molecular mass (sum of all relative atomic masses) i.e. Mr of CuCl2 = 63.5 + (2x35.5) =134.5

Quite a fundamental formula that you should certainly know!
Thank you!!!
12. (Original post by Fallen99)
Sorry but the method is right I just did it again with the balanced equation and the answer is
Use this formula= mass= moles*relative formula mass
So first work out the relative formula for each of them. Lets start with CuCl2
Cu= 63.5
Cl= 35.5*2= 71
Than it is 2NaNO3
Na= 23*2=46
Nitrogen= 14
Oxygen =16*3 = 48
Add the relative formula mass of CuCl2+NaNO3 together= 242.5
And you have the total mass of 15+20=35 grams
Use this to work out moles which is mass/ relative formula mass
Moles= 35/242.5= 0.1443298962
Now work out the relative mass for 2NaCl
Na= 23*2= 46
Cl= 35.5*2= 71
For this you have to find mass which is moles* relative mass
0.1443298962*117= 13.37659786
So 13.37659786 Nacl can be formed
Thank you very much!!! Something that I actually understand.
13. (Original post by Wolfram Alpha)
Thank you very much!!! Something that I actually understand.
U r welcome but I don't know if my answer is right because according to Dylaan it is wrong

Posted from TSR Mobile
14. (Original post by Wolfram Alpha)
Thank you very much!!! Something that I actually understand.
That working out is incorrect, look at mine instead.

Posted from TSR Mobile

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: March 1, 2015
Today on TSR

### Four simple steps to get an A*

Here's all you have to do

### University open days

• University of East Anglia
All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
Wed, 30 Jan '19
• Aston University
Wed, 30 Jan '19
• Solent University
Sat, 2 Feb '19
Poll
Useful resources

## Study tools

### Essay expert

Learn to write like a pro with our ultimate essay guide.

See where you can apply with our uni match tool

### Make study resources

Create all the resources you need to get the grades.

### Create your own Study Plan

Organise all your homework and exams so you never miss another deadline.

### Resources by subject

From flashcards to mind maps; there's everything you need for all of your GCSE subjects.

### Find past papers

100s of GCSE past papers for all your subjects at your fingertips.