AS Chemistry- helping each other out!
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Original post by samb1234
My school doesn't have half term this term.
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Original post by BBeyond
Ikr so close now 
I find it beyond stupid that I can go from 77-80 on unit 1 papers to struggling to reach 60 on unit 2 papers when I've put far more time into unit 2...
I find it beyond stupid that I can go from 77-80 on unit 1 papers to struggling to reach 60 on unit 2 papers when I've put far more time into unit 2...
And funnily enough the grade boundaries aren't that much lower
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Original post by C0balt
If lower at all, quite a lot of papers seem to have higher boundaries, it truly puzzles me tbh.
We did another unit 1 and unit 2 mock for chem, i think it was unit 1 2013 may paper and last years unit 2 paper. The unit 1 seemed far harder than the unit 2 one, the unit 2 one was pretty easy.
hey guys can you help me out with something,
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
Original post by wil97
hey guys can you help me out with something,
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
Barium chloride tests the presence of sulphate ion. Positive result gives a white precipitate of barium sulphate. Don't you add nitric acid before addition of barium chloride to eliminate he possibility of carbonate or hydrogen carbonate ions. If carbonate or hydrogen carbonate ions are present there will be fizzing, which is carbon dioxide.
Silver nitrate is the test for halide ions. With the presence of chloride ion white precipitate forms, with bromide cream precipitate, and with iodide yellow precipitate. White precipitate dissolves in both dilute and concentrated ammonia, cream precipitate only dissolves in concentrated ammonia and yellow precipitate does not dissolve in ammonia. Nitric acid is added BEFORE the addition of silver nitrate to eliminate the possibility of other ions as said above.
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Original post by wil97
hey guys can you help me out with something,
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
let's say in a practical you were given a few unknown substances and you had to do these tests on them:
1. add barium chloride, record result then add dilute nitric acid + record result
2. add silver nitrate, record result then add dilute nitric acid + record result
and the results were white, cream, yellow precipitates that either dissolves after the dilute nitric acid or didnt, and one substance which showed fizzing...what would any of this mean. hypothetically.
If you add barium chloride and get a white precipitate, your original sample contained sulphate (SO4^2- ions).
When you add dilute nitric acid then silver nitrate and you get:
White precipitate = chloride ions (Cl-)
Cream precipitate = bromide ions (Br-)
Yellow precipitate = iodide ions (I-)
If you aren't confident with the colours, you can do another test with the silver halides, as they have different solubilities in aqueous ammonia.
AgCl dissolves in dilute and concentrated ammonia
AgBr is partially soluble/doesn't dissolve in dilute aqueous ammonia but does dissolve in conc aqueous ammonia.
AgI doesn't dissolve in either
Hope this helps!
Doing a physics past paper and my inner chemist was stimulated.
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Original post by C0balt
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Haha 😄.When we did semi conductors my inner chemistry was stimulated.
Original post by Kadak
Oh yeah
same with excitation - I was like "flame tests 
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Hello again, so I came across a question that im confused on
I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
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I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
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Original post by TeaAndTextbooks
Hello again, so I came across a question that im confused on
I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
Posted from TSR Mobile
I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
Posted from TSR Mobile
Have you got the full question to post up? There must be additional information given in earlier parts of the question that will help in getting the answer for this part.
When they say HX I assume it must be a hydrogen halide but that clearly isn't the case if it only contains Carbon, Hydrogen and Oxygen.
It possible could be an alcohol with an OH group (or even multiple OH groups!); a carboxylic acid.
Original post by TeaAndTextbooks
Hello again, so I came across a question that im confused on
I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
Posted from TSR Mobile
I calculated the molar mass of a compound to be 200 and then it asks you to
Suggest the formula of the acid HX given that it only contains C, H and O
Please show your working out.
Thank you
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See the attached.
Assumed the acid to be carboxylic acid (it could've been carbonic acid but it doesn't add up to 200). It is weird that it is shown to be HX though.
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(edited 9 years ago)
Original post by C0balt
Haha for me it was the other way round. In one chemistry paper it asked why different elements burned with different colours so I obviously had to include the formula giving the wavelength of the emitted photon
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Original post by C0balt
Assumed the acid to be carboxylic acid (it could've been carbonic acid but it doesn't add up to 200). It is weird that it is shown to be HX though.
Assumed the acid to be carboxylic acid (it could've been carbonic acid but it doesn't add up to 200). It is weird that it is shown to be HX though.
Original post by James A
When they say HX I assume it must be a hydrogen halide but that clearly isn't the case if it only contains Carbon, Hydrogen and Oxygen.
When they say HX I assume it must be a hydrogen halide but that clearly isn't the case if it only contains Carbon, Hydrogen and Oxygen.
Things like HA and HX are often used in secondary school chemistry to represent hypothetical carboxylic acids that dissociate into H+ and A- respectively.
Original post by samb1234
Haha for me it was the other way round. In one chemistry paper it asked why different elements burned with different colours so I obviously had to include the formula giving the wavelength of the emitted photon
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Hahaha
That flame test thought was in lesson though. We learnt excitation later than flame tests that's why
I haven't come across with the flame test question yet, so I'll see if I get the urge.
But I'm pretty sure I will now say photons instead of electromagnetic wave which I used to say at the beginning of the year.
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Original post by Hype en Ecosse
Things like HA and HX are often used in secondary school chemistry to represent hypothetical carboxylic acids that dissociate into H+ and A- respectively.
Never come across that lol only HX I have seen was halides in my AS course
Now I won't randomly assume in my exams, great
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Original post by C0balt
Hahaha
That flame test thought was in lesson though. We learnt excitation later than flame tests that's why
I haven't come across with the flame test question yet, so I'll see if I get the urge.
But I'm pretty sure I will now say photons instead of electromagnetic wave which I used to say at the beginning of the year.
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That flame test thought was in lesson though. We learnt excitation later than flame tests that's why
I haven't come across with the flame test question yet, so I'll see if I get the urge.
But I'm pretty sure I will now say photons instead of electromagnetic wave which I used to say at the beginning of the year.
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I do the same thing with coulombs law for any ionisation energy question
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Original post by samb1234
What board are you with for physics?
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Thanks alot that was helpful I think I understand it now. It was just a class question so my teacher probably worded it wrong but I'm sure your answer is correct.
(edited 9 years ago)
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