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    (Original post by wednesday_adams)
    " state two essential conditions used for the extraction of aluminium from aluminium oxide "

    anyone?
    This will be aluminium oxide (bauxite) extracted by electrolysis
    so the conditions may be
    with Molton cryolite to lower melting point
    high tenperatures
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    How an earth do you answer shape of molecule questions?

    ( EVERY single question I do I get no marks for it)

    Help!


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    (Original post by emilita.nxn)
    How an earth do you answer shape of molecule questions?

    ( EVERY single question I do I get no marks for it)

    Help!


    Posted from TSR Mobile
    Try this if you still need help let me know http://www.chemguide.co.uk/atoms/bonding/shapes.html

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    (Original post by wednesday_adams)
    " state two essential conditions used for the extraction of aluminium from aluminium oxide "

    anyone?

    The aluminium oxide is electrolysed - so an essential condition is that it must be molten. Another important factor is that it has to be mixed with cryolite - this has a much lower melting temperature so it the resulting mixture takes less energy for it to melt
    That's what you need to know for AQA AS, I don't know about any other exam boards
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    thanks friendd
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    (Original post by emilita.nxn)
    How an earth do you answer shape of molecule questions?

    ( EVERY single question I do I get no marks for it)

    Help!


    Posted from TSR Mobile
    Basically a template:

    X bonding pairs,
    Y lone pairs,
    Electron pairs repel,
    Lone pairs repel more

    Insert X and Y accordingly and you're set

    If they ask for shape, state the shape:

    [2 bonding pairs-linear
    3- trigonal planar,
    4- tetrahedral,
    6-octahedral
    when there are no lone pairs

    2 bonding and 1/2 lone pairs- non-linear
    3 bonding and 1 lone pair- pyramidal]

    And then repeat the template :lol:
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    For titrations what is the table you have to do. I have the empa coming up
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    For titrations what is the table you have to do. I have the empa coming up
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    (Original post by Super199)
    For titrations what is the table you have to do. I have the empa coming up
    Generally, you'd have the first column as being titre (this starts with 'rough' then 1, 2, 3 etc). The next column should be start volume, then finish volume, then you work out the volume used. If you are doing this multiple times, you could also have an average titre column.
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    does anyone have chemistry unit 3B notes, as in detailed ones about core practicals??
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    what are you predicted so far??
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    hi i got a question to ask,
    does anyone know the percentage yield difference formula??
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    (Original post by HToo)
    hi i got a question to ask,
    does anyone know the percentage yield difference formula??
    Like how to calculate % yield?

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    % yield = actual yield (obtained from carrying out experiment) / theoretical yield (calculated from the numbers provided in the question)

    If you have a specific question that you're stuck on, I could work it out for you and show you the stages if you want.


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    [QUOTE=Fiellabella;55002821]% yield = actual yield (obtained from carrying out experiment) / theoretical yield (calculated from the numbers provided in the question)

    If you have a specific question that you're stuck on, I could work it out for you and show you the stages if you want.


    Posted from TSR Mobile[/QUOTma]

    Example I made the other day to help someone

    I can help you. Example question:

    The equation for the reaction of CuCO3 and H2SO4 is shown below:

    CuCo3 +H2SO4 goes to H2O + CO2 + CuSO4.

    Given that John reacts 2.2g of CuCO3, calculate the theoretical yield of CuSO4.

    Solution: the first thing to do is look at the mole ratios of each of the reactants and products. In this case, there is 1 mole of everything (large number in front of the formula is the no of moles) so it follows that the number of moles of CuCO3 must = no of CuSO4. Next, calculate how many moles of CuCO3 you have by dividing 2.2 by the total Mr of CuCO3 (don't have a calculator so I'll leave it like that). You now know the no of moles of CuCO3 and hence the number of moles of CuSO4. To work out the theoretical yield, multiply the number of molesby the total Mr of CuSO4.

    Question 2: After experiment, John weighed his CuSO4 crystals and found that he had 0.6g of crystals. Calculate the % yield.

    Solution: % yield = theoretical yield/actual yield *100

    Hope that helps

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    Anyone done ocr f322 JANUARY 2011 question 3ciii? Why does the result for enthalpy change of reaction have to be multiplied by 2? Shouldn't it just be per mole?


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    (Original post by anoymous1111)
    Anyone done ocr f322 JANUARY 2011 question 3ciii? Why does the result for enthalpy change of reaction have to be multiplied by 2? Shouldn't it just be per mole?


    Posted from TSR Mobile
    You might get a quicker response if you uploaded a screenshot or something

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    Name:  ImageUploadedByStudent Room1429052102.812084.jpg
Views: 167
Size:  61.9 KB

    I don't understand part ciii.... normally I find these calculations easy and I worked out what I thought was the enthalpy change per mole. However on the mark scheme this answer is multiplied by 2. I can see in the equation there is a 2NH4SCN, but I thought it would still just be the enthalpy change per mole. Surely multiplying it by 2 means it isn't the enthalpy change per mole? Do you always have to do this with enthalpy of reaction questions?


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    Often this is because of a 2:1 molar ratio
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    (Original post by anoymous1111)
    Name:  ImageUploadedByStudent Room1429052102.812084.jpg
Views: 167
Size:  61.9 KB

    I don't understand part ciii.... normally I find these calculations easy and I worked out what I thought was the enthalpy change per mole. However on the mark scheme this answer is multiplied by 2. I can see in the equation there is a 2NH4SCN, but I thought it would still just be the enthalpy change per mole. Surely multiplying it by 2 means it isn't the enthalpy change per mole? Do you always have to do this with enthalpy of reaction questions?


    Posted from TSR Mobile
    http://gyazo.com/e29c3ce9c8848d8c7e45ec70dacdad2e per mole accepted
 
 
 
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