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

    0
    ReputationRep:
    I've been trying to do one of the multiple choice questions from the ocr specimen paper (new spec), but have no clue how to go about it:
    A student mixes 100 cm^3 of 0.200 mol dm^-3 NaCl (aq) with 100 cm^3 of 0.200 mol dm^-3 Na2CO3 (aq). What is the total concentration of Na+ ions in the mixture formed?
    The answer ends up being 0.300 mol dm^3.
    Thanks in advance
    Offline

    0
    ReputationRep:
    n(NaCl) = c x V(decimetres3)
    = 0.200 x (100/1000)
    = 0.02 mol
    There is one Na+ ion per unit, so n(Na+) = n(NaCl) = 0.02 mol

    n(Na2CO3) = 0.200 x (100/1000)
    = 0.02 mol
    There are two Na+ ions per unit, so n(Na+) = 2 x n(Na2CO3) = 0.04 mol

    Total number of Na+ ions = 0.02 + 0.04
    = 0.06 mol

    Therefore concentration of mixture = n/V
    There is now 200cm3 on total, which is 0.2 dm3, so:
    0.06 mol / 0.2 dm3 = 0.300 mol dm-3
    • Thread Starter
    Offline

    0
    ReputationRep:
    Thank you!
 
 
 
  • 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
    Has a teacher ever helped you cheat?
  • 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.