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

    0
    ReputationRep:
    I am okay with part a) but I do not know how to calculate part b).. It would be really helpful if one of you could help me on this. I've got a mark scheme so it would be nice where these numbers come from (i.e. 2 and 72)..

    Thanks!

    16. Airbags, used as safety features in cars, contain sodium azide, NaN3. An airbag requires

    a large volume of gas to be produced in a few milliseconds. The gas is produced in this

    reaction:

    2NaN3(s) -> 2Na(s) + 3N2(g) ????H is positive

    When the airbag is fully inflated, 50 dm3 of nitrogen gas is produced.

    (a) Calculate the number of molecules in 50 dm3 of nitrogen gas under these conditions.

    [The Avogadro constant = 6.02 ???? 1023 mol–1. The molar volume of nitrogen gas under

    the conditions in the airbag is 24 dm3 mol–1].


    (b) Calculate the mass of sodium azide, NaN3, that would produce 50 dm3 of nitrogen

    gas.



    The answer is:



    Mr = 23 + 42 = 65

    Mass = (2 * 65 * 50/72) = 90g



    But I don't know where 2 and 72 comes from in the mass equation.
    • Study Helper
    Offline

    17
    ReputationRep:
    looks like you times it by 2 because you have two moles, I havent looked at this much, but im guessing mass=moles*Mr, is this what you've done?
    Offline

    0
    ReputationRep:
    Times by two because you have 2NaN3

    Could the 72 come because you've 3N2's, one mole of gas occupies 24dm^3
    3*24=72?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Kat_Heine)
    Times by two because you have 2NaN3

    Could the 72 come because you've 3N2's, one mole of gas occupies 24dm^3
    3*24=72?
    Ah, I see. Thank you so much!!
 
 
 
  • 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
    Will you be richer or poorer than your parents?
  • 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

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