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

    17
    ReputationRep:
    Hi. I answered this exam question, and I managed to get the correct answer. However, I am just wondering if my method was correct and the reason behind it was also correct.

    The question was: An isotope of sodium has a relative isotopic mass of 23.0. Calculate, to three significant figures, the mass, in grams, of a single atom of this isotope of sodium (the Avogadro constant is 6.02 x 10^23 mol^-1).

    I knew that molar mass was mass per mole. For sodium, it was 23.0. Avogadro's constant = 6.02x10^23 which is number of atoms per mole.

    I thought to find the mass, I would turn Avogadro's constant into 1 since I only want 1 atom, so I divide by 6.02x10^23 and I would do the same to molar mass of sodium to get 23/6.02x10^23.

    I'm not sure if i've just made things complicated, but if there's a simpler reason behind dividing 23/6.02x10^23 then please explain. Thank you.
    Offline

    16
    ReputationRep:
    If the molar mass is 23.0 per mole, then we can say that:

    n=m/Mr

    1= m/23

    => m = 23 grams

    This means that the mass of 6.02*10^23 atoms of sodium is 23 grams.

    So to find one atom, you can just use ratios:

    6.02*10^23 atoms : 23 grams

    => 1 atom : 23/(6.02*10^23) grams
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by Welshstig)
    If the molar mass is 23.0 per mole, then we can say that:

    n=m/Mr

    1= m/23

    => m = 23 grams

    This means that the mass of 6.02*10^23 atoms of sodium is 23 grams.

    So to find one atom, you can just use ratios:

    6.02*10^23 atoms : 23 grams

    => 1 atom : 23/(6.02*10^23) grams
    Is that sort of what I did then? Thanks for the reply.
    Offline

    16
    ReputationRep:
    (Original post by Xenice)
    Is that sort of what I did then? Thanks for the reply.
    Exactly what you did!
 
 
 
  • 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
    What newspaper do you read/prefer?
  • 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.