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Chemistry - The Mole Concept

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  • 15-09-2010 12:11am
    #1
    Coeurdepirate
    Registered Users Posts: 2,576 ✭✭✭


    We've just finished the Mole Concept in Chemistry, and I'm really annoyed because I understand everything perfectly, I just don't know how to distinguish between the questions and what calculations you do for each. Does anybody have any tips?


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    #2
    Fizzical
    Registered Users Posts: 262 ✭✭Fizzical


    Sorry, but if you don't understand the questions then you don't understand the concept!

    Remember: 1 mole = 6 x 10^23 particles = Mr in grams = 22.4 litres of gas.

    Also, 'particles' means molecules or atoms or ions. So, if you have 6 x 10^23 molecules of O2 that means you have 12 x 10^23 atoms of O. Also, if you have 6 x 10^23 molecules of Na2SO4 then you have 12 x 10^23 Na ions.

    Otherwise, just keep practising worked examples till you figure what the questions mean.

    Moles are important for the rest of the course but, equally, when you do the rest of the course it helps you understand moles better - more practice in real situations.


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    #3
    Maestoso
    Registered Users Posts: 35 ✭Maestoso


    I know what you mean.
    A good place to work from might be to consider all possible directions.

    Moles --> Atoms/Molecules: Multiply by 6x10^23 (note that if they ask you specifically for the number of atoms, you must multiply by that number of atoms given. Like, if you have two sodium atoms, you multiply your answer by two. You don't have to do anything extra if they ask "molecules" though)
    Atoms/Molecules --> Moles: Divide by 6x10^23
    Moles --> Grams: Multiply moles by relative mass of element/compound
    Grams--> Moles: Divide mass of the substance being measured by relative atomic mass of element/compound

    Summarising: Converting from moles to something else, multiply.
    Converting from anything else to moles, divide.
    Moles/Grams involves relative atomic masses.
    Moles/Atoms/Molecules involves Avogadro's constant.

    Perhaps draw out a sort of diagram-map so you can take quick glances at it from time to time to keep things fresh.

    Like this: Atoms/Molecules <
    > Moles <
    > Grams

    And then include the calculations over the arrows.

    Good luck. I only bothered with those calculations. I didn't worry about the "Miscellaneous" problems like the ones in 'Chemistry Live!' because it took me so long to grasp that stuff above by myself.


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