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    anyone got a color code list that is matched with the mark scheme? mines is always wrong
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    know that MCO3 is formed but that M2(CO3)3 is not formed

    I dont Understand what we need to know about this. Which one is a metal (3) carbonate and which one is a metal (2) carbonate? Can anyone explain it?
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    Gah- Kill me.
    Dreading this exam.

    I've been obsessing over Biology for too long, and have neglected Chem.

    All I need is a C. But I doubt i'll even get that... ):
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    (Original post by aurelia_koll)
    anyone got a color code list that is matched with the mark scheme? mines is always wrong
    Hey would this help? sorry if ive misunderstood
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    (Original post by Hannah098)
    know that MCO3 is formed but that M2(CO3)3 is not formed

    I dont Understand what we need to know about this. Which one is a metal (3) carbonate and which one is a metal (2) carbonate? Can anyone explain it?
    The first one is a metal (2) carbonate and the second is a metal (3) carbonate but the second one doesn't exist.

    A carbonate ion exists as CO3(2-) so has a charge of -2. Thus logically to form neutrally charged molecules with a M2+ ion it would form MCO3 (such as CuCO3) and with a M3+ ion you would think it would be:

    2M3+ + 3CO3(2-) --> M2(CO3)3

    However this doesn't happen because Metal 3+ ions are more acidic than Metal 2+ ions so rather than going through a precipitation reaction with CO3(2-) (which metal 2+ ions do because they're not acidic enough) it has an acid-base reaction (just like when a carboxylic acid reacts with a carbonate).

    You end up with a similar reaction to the ones where aqueous M3+ ions react with dilute NH3 or NaOH as these are acid-base reactions, where 3 hydrogen atoms are removed from the water molecules in the complex and a hydroxide solid is formed.

    The 6 reactions you need to know for carbonates can be split into M2+ and M3+ reactions:

    [Cu(H2O)6]2+ +CO3(2-) --> CuCO3 + 6H2O
    Blue solution to blue-green precipitate.

    [Fe(H2O)6]2+ +CO3(2-) --> FeCO3 + 6H2O
    Pale green solution to green precipitate.

    [Co(H2O)6]2+ +CO3(2-) --> CoCO3 + 6H2O
    Pink solution to pink precipitate

    And then

    2[Al(H2O)6]3+ +3CO3(2-) --> 2Al(H2O)3(OH)3 + 3H2O + 3CO2
    Colourless solution to white precipitate and effervescence

    2[Cr(H2O)6]3+ +3CO3(2-) --> 2Cr(H2O)3(OH)3 + 3H2O + 3CO2
    Ruby (or for the guaranteed mark green) solution to green precipitate and effervescence

    2[Fe(H2O)6]3+ +3CO3(2-) --> 2Fe(H2O)3(OH)3 + 3H2O + 3CO2
    Pale violet (or for guaranteed mark yellow) solution to brown precipitate and effervescence

    Hope this has helped a smidge
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    (Original post by James1313)
    Gah- Kill me.
    Dreading this exam.

    I've been obsessing over Biology for too long, and have neglected Chem.

    All I need is a C. But I doubt i'll even get that... ):
    Haha, we both need low grades and we're still worried.
    Think about it this way, you need something like 55/100 to get a C.
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    Looking through past papers and stuff, there never seems to be much on Electrochemical cells Chapter 14.4 in the textbook. Any one have any ideas on how they could question us on this??
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    (Original post by Raimu)
    Haha, we both need low grades and we're still worried.
    Think about it this way, you need something like 55/100 to get a C.
    True, true.

    This is what keeps me going!
    Haha.

    It's just a lot of memorising in this module, and I don't have the best memory,

    And i'm expecting a lot of synoptic questions!

    Anyway- Good luck!
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    Doe anybody please have any advantages and disadvantages for:
    Non Rechargeable Cells
    Rechargeable Cells
    Portable Batteries

    Because my book is a load of pants....lol
    Thanks in advance (+Rep)
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    I need an A in this unit. I probably need about 90/120 UMS for it!! :shock:

    Hmm 70/100 raw marks. Doesn't look easy at all tbh. The very first paper is hard!!
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    (Original post by Veem)
    Looking through past papers and stuff, there never seems to be much on Electrochemical cells Chapter 14.4 in the textbook. Any one have any ideas on how they could question us on this??
    I hate this part, I have no idea what to learn about in this section!! :p:
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    (Original post by Sparkly-Star)
    I hate this part, I have no idea what to learn about in this section!! :p:
    Lol what is it about? I don't have that text book and now I'm curious/worried
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    are people just learning all the equations for metal oxides, or do people have a technique for working them out...i really dont have this deeper understanding of chemistry that some people do
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    I need 20% for an A, but just over 80% for an A*! thats a jump in grade boundaries and a half! :P
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    (Original post by jimmy303)
    Lol what is it about? I don't have that text book and now I'm curious/worried
    Non-rechargeable batteries
    Rechargeable batteries
    Portable Batteries
    Fuel Cell
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    (Original post by Veem)
    Non-rechargeable batteries
    Rechargeable batteries
    Portable Batteries
    Fuel Cell
    Dont think you need to know all of that, just need to be able to manipulate the equations and work out e.m.f's and all of that!
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    (Original post by uzzy18)
    are people just learning all the equations for metal oxides, or do people have a technique for working them out...i really dont have this deeper understanding of chemistry that some people do
    It's not a 'deeper understanding', it's looking for a pattern

    Split the 6 you need to now, Fe,Co,Cu,Al,Fe,Cr. Notice Fe is twice.....

    Split it into 2 groups - 2+ ions: Fe,Co,Cu
    And 3+ ions: Al,Fe,Cr

    They're all solutions, metal(H2O)6 2+'s - learn each one's colours, in order, the solution colours are: Green, Pink, Blue, Colourless, Yellow, Violet

    Understand what happens when you add
    1) OH or NH3
    2) OH specifically in XS
    3) NH3 specifically in XS
    4) Na2CO3

    Make 2 separate papers, 1 for 2+ and 1 for 3+

    Understand the backbone of 2+ and 3+ reactions:
    eg - 2+ ADD 1) --> metal(H20)4(OH)2, whereas 3+ is metal(H20)3(OH)3... hey! hang on, these are the same for 3+ and Na2CO3. Look for links like these.

    Write out the reactions separately, ones where there are no change, and ones where they are. Like I said, just write the product - if you need to write out the whole equation, then you're not getting the general picture. Learn the **RULES** - for this, it's all covered in 2 pages on the CGP revision guide. Stupid NT book, turns the most simplest thing into something that looks dreadful.

    Once you understand the 'backbone' rules, you'll automatically know what the reaction generally looks like. Learn the reactions which start off with M(H20)6 2+/3+ - and replace the M with the metals, Fe,Co,Cu,Al,Fe,Cr.

    I started off just like you, totally lost - I just organised it, looked for links that I understood, and then whacked on some colours. Now, I just see it in my head, and it's easy recall from there. All the effor goes in learning the general M equation rules, and colours.
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    Hi has anyone done the last question of the CHEM5 Jan 11 paper. After you work out moles of H2O2, why do you multiply by 10 and then by 1000/5?
    Because I am so confused --> :confused:
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    (Original post by jimmy303)
    Lol what is it about? I don't have that text book and now I'm curious/worried
    The bit about batteries!! :p:
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    What's the reaction with aluminum and sodium carbonate? I think my notes are wrong as they produce two (aluminum h20)6 instead of one
    Also do we need to know reactions with hcl?
 
 
 
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