You are Here: Home

# Percentage yield calculation with gases

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. Hello, I'm currently revising unit 1 as a resit. Been fine with all the other multiple choice questions but this one (from last year's paper):
Lithium reacts with water to produce hydrogen.Li(s) + H2O(l) → LiOH(aq) + ½H2(g)

(a) In an experiment, 0.069 g (0.01 mol) of lithium produced 90 cm3 of hydrogen at room temperature and pressure. What is the percentage yield of hydrogen?

[1 mol of any gas occupies 24 dm3 at room temperature and pressure.]
I can't seem to get the right answer, which was 75%. I managed to get 75% after looking at the answer, but the method I used is unusual...

Is there an actual method for doing this, without me doing these random calculations that somehow got the answer (which I don't understand how)?

I've done this weird method which involved me doing
0.01 * 24 = 0.24
0.24 * 1000 = 240
90/240 = 0.375 * 2 = 0.75
0.75*100 = 75% which is the right answer
2. Ratio of Lithium to Hydrogen gas is 1:0.5

Therefore, the moles of Hydrogen gas is half the moles of lithium. ( moles = 0.005)

volume of gas = moles * 24000 = 0.005 * 24000 = 120cm3

percentage yield = (90/120) * 100 = 75%

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 2, 2016
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:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Q&A with Paralympian Jack Rutter

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.