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Chemistry Calculation Help Needed!

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  • 06-04-2014 8:08pm
    #1
    yoyojc
    Registered Users Posts: 278 ✭✭


    Hi, I have a stochiometry test tomorrow I need help!

    Do you know when you are calculating lets say - no of moles which is mass divided by mr.

    I'm confused by the mr. If I see 2BeCl (made up). I ignore the 2 and just get the rel atomic mass of Be plus Cl and add it..
    But if it was something like BeCl2 (small two) do I add Be mass and Cl mass by 2.. Or is it just BeCl ignore the 2..

    Is it basically the mr for ONE mole of it? Just confused as to what I use for mass in g?

    Any help would be gladly appreciated :)


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    #2
    Ompala
    Registered Users Posts: 899 ✭✭✭Ompala


    yoyojc wrote: »
    Hi, I have a stochiometry test tomorrow I need help!

    Do you know when you are calculating lets say - no of moles which is mass divided by mr.

    I'm confused by the mr. If I see 2BeCl (made up). I ignore the 2 and just get the rel atomic mass of Be plus Cl and add it..
    But if it was something like BeCl2 (small two) do I add Be mass and Cl mass by 2.. Or is it just BeCl ignore the 2..

    Is it basically the mr for ONE mole of it? Just confused as to what I use for mass in g?

    Any help would be gladly appreciated :)

    If you see 2BeCl, that means 2 moles of BeCl, but the Mr will still just be that of BeCl, because Mr is just for one mole.
    For BeCl2, we have 1 atom of beryllium and 2 chlorine atoms, so we have to add the mass of them to get the Mr for one mole.
    The units for Mr are g per mole, meaning it is just for one mole.


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    #3
    yoyojc
    Registered Users Posts: 278 ✭✭yoyojc


    thanks so much cleared it up for me:)


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    #4
    EoghanIRL
    Registered Users Posts: 4,080 ✭✭✭EoghanIRL


    yoyojc wrote: »
    thanks so much cleared it up for me:)

    It's seems you don't understand what the two meant in the first place .

    It plays a role in the reacting ratio.
    Say you have the limiting agent and you want to find the number of moles / gramms of another compound formed in the reaction . Firstly it will be dependent on the number of moles of the limiting agent present and then you would multiply that numbers of moles or grams by the reacting ratio .

    So 2 moles of BeCl would react with x moles of the limiting reagent or a different reactant and so on.....


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    #5
    yoyojc
    Registered Users Posts: 278 ✭✭yoyojc


    EoghanIRL wrote: »
    It's seems you don't understand what the two meant in the first place .

    It plays a role in the reacting ratio.
    Say you have the limiting agent and you want to find the number of moles / gramms of another compound formed in the reaction . Firstly it will be dependent on the number of moles of the limiting agent present and then you would multiply that numbers of moles or grams by the reacting ratio .

    So 2 moles of BeCl would react with x moles of the limiting reagent or a different reactant and so on.....
    Thank you, I've done alot of work around the chapter since then and I've a great understanding now :) sometimes its important to ask the 'easy' questions to comprehend the difficult ones :)


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