Join TSR now and get all your revision questions answeredSign up now
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hello

    I would like to ask something quite simple but I can't get my head around it. If I have 2 cm^3 of iodine, HCL and water together with 4cm^3 of propanone. What is the concentration of iodine in mol dm^-3?
    Offline

    0
    ReputationRep:
    Firstly, what you need to tackle is your units. In chemistry it tends to be in decimeters for volume.

    First change 2cm^3 to dm^3
    1cm^3 = 0.001dm^3
    so,
    2cm^3 = 0.002dm^3

    Plugging into our equation gives us:
    n = c x 0.002dm^3

    You have your volume there but tbh you don't have a lot of information to go on without a molar ratio.

    Did you mean you have 2cm^3 of Iodine on it's own, or 2cm^3 of Iodine, HCl and water all together in solution?
    The latter is not possible as you don't know what the composition of those substances in that 2cm^3 is. You need more information either in the form of individual volumes for the Iodine, HCl and water or moles, etc.

    I don't want to confuse you but if it's the former, it could be roughly worked out by this method and using your trusty periodic table:

    1 mole of Iodine has a mass of 127.00grams (this is the molar mass) so if you're calculating for 2cm^3 of iodine
    then you can do the calculation of n = Mass/Molar Mass

    2cm^3 or 0.002dm^3 is roughly equivalent to 2 grams
    so moles = mass/molar mass:
    2/127 = 0.015 moles of Iodine

    Then rearrange n = c x v, to make c the subject

    n/v = c

    0.015/0.002 = 7.5 mol/dm^3 or (mol dm ^-3)

    But yeah, you don't have all the necessary information there. Is this a problem from a teacher or exam question? Might be helpful to see it.
 
 
 
Poll
Which Fantasy Franchise is the best?

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.