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Edexcel - Chemistry Unit 2 - 4 June 2013

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Original post by kevsamuel
is magnesium carbonate more soluble in water than calcium carbonate?


All carbonates are insoluble in water.
Original post by Polish master
For the question about identifying MgCO3 and the other one I cant remember now It was ok to distinguish the two by using Lime water and seeing which one took longer to make it cloudy ? That's what I put and I'm pretty sure it would be acceptable


Thankyou theres someone at least who did the same thing as me. Exactly this one makes more sense.
Original post by jollygood
Exactly I just don't understand why everyone is saying Although the question said without heating but still it should be a flame test.


The mark scheme will obviously prove me wrong, and I'm more than happy for it to do so but I cannot understand how a question which explicitly says "without heat" will accept a flame test. The whole premise of a flame test is to use heat. :s-smilie:

FYI. I am talking about the second question, not the first where you had to give an equation.
I think the main way was to add NaOH(aq)... BaCO3 will form a green precipitate and MgCO3 will form a white precipitate
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Meehar17
Original post by jollygood
Thankyou theres someone at least who did the same thing as me. Exactly this one makes more sense.

yeah I did the exact same thing as well because magnesium is quicker to form the oxide and turn the limewater cloudy.... this one actually makes sense
It surely has to be the flame test. Unless and until someone comes up with a viable, realistic alternative that is in the actual spec (!), then we have to say it's the flame test.
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Meehar17
I think if someone had the paper and uploaded it we would all have an idea of what grade we would be getting
I just really want to see the paper again ;_;
Also can someone answer my question?

Do you think they would accept brown to colourless for the iodine titration one? Or only pale yellow to colourless?
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Original post by alby37135
I think the main way was to add NaOH(aq)... BaCO3 will form a green precipitate and MgCO3 will form a white precipitate


Knowing baco3 is green is A2...


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Original post by xstarsx67
Oh ma, for some stupid reason I put it makes barium oxide and hydrogen, instead of barium hydroxide... D: I'm so stupid - how many marks was that? 2?


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I'm not sure, if it asked for state symbols then probably 2.
Original post by shan94
Hi would it matter if you put multiples?
Thanks.


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According to the previous mark schemes thats fine :smile: In equations there's always "Accept multiples"
Original post by James A
All carbonates are insoluble in water.

But then why do you think the test in the last part was a solubility test? :/ I really hope they accept flame tests too :smile: when I read that question I thought by "heat" they meant like, a thermal decomposition test or something.
Original post by Kurraiyo
But then why do you think the test in the last part was a solubility test? :/ I really hope they accept flame tests too :smile: when I read that question I thought by "heat" they meant like, a thermal decomposition test or something.


If you react it with another sulfate, then you would get a displacement reation, wouldn't you?
I think we should stop arguing about this flame test question guys. its just stressing us all out. Any ideas what raw marks are needed for full UMS?
I want to know for titration question I put that for the end point that the colour of solution will become really pale brown. would that be acceptable? because it goes colourless when starch indicator is present!! any ideas?
What did everyone put for fullerene mcq ? I was so confused between first and second option but finally I chose the 2nd one the one which says fullerenes are small molecules?
Original post by James A
If you react it with another sulfate, then you would get a displacement reation, wouldn't you?


We would, but that would be weird considering we were supposed to answer "white precipitate due to barium sulfate formation" just on the previous page. XD
Original post by jollygood
Thankyou theres someone at least who did the same thing as me. Exactly this one makes more sense.


A fair few people from my school did the same thing dont worry haha
Original post by jollygood
I think we should stop arguing about this flame test question guys. its just stressing us all out. Any ideas what raw marks are needed for full UMS?

I'd guess 75-76.

Original post by jollygood
I want to know for titration question I put that for the end point that the colour of solution will become really pale brown. would that be acceptable? because it goes colourless when starch indicator is present!! any ideas?

I'm pretty sure it goes colourless sorry, starch just makes it clearer :frown:
Original post by samsimmons
I'd guess 75-76.


I'm pretty sure it goes colourless sorry, starch just makes it clearer :frown:


But why did they ask that what would be colour change in absence of starch indicator? there must be something different about it.

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