Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    13
    ReputationRep:
    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
    Offline

    15
    ReputationRep:
    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%
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Brexit voters: Do you stand by your vote?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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