A-level Chemistry Revision Squad!

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I remember like this, oxidising agents are elements like OXYgen. Oxygen needs only 2 electrons to gain full shell stability so since it gains it gets reduced. If it gets reduced it oxidises others therefore its an oxidising agent

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Reply 461

9307914

Original post by wb236

Hey, wondered if anyone could clear this up for me,

Going over past papers for Chem6x I've come across drawing graphs for the Iodine clock reaction a few times, usually pretty straightforward, log (1/t) is plotted on the y-axis and Log(volume) on the x-axis, but I noticed in the mark scheme that says a mark is lost if the y-axis is plotted with ascending negative numbers? I'm not sure if the wording is awkward but the y-values for Log91/t) are usually negative, it doesn't seem to make sense to plot them in a descending scale (i.e. negative values getting more negative going up the y-axis),

Cheers

I think that you have to plot the graph with the axis at the top if you see what i mean, so like a normal axis but upside down and then put your negative values on the y axis getting more negative as you go down

Reply 462

djmans

guys please help
what happens if a piece if a piece of sodium is added to an alcohol

Reply 463

djmans

Original post by A.S.J

Chemistry exam day after tomorrow(toms bio) need so many prayers. I'm so worried...

can anyone give me a brief on carbon 13 nmr? its new in our syllabus and ur teacher....... by the way its Alevel

AS or A2

Reply 464

Cpj16

http://www.thestudentroom.co.uk/showthread.php?t=4068049
_{Help me you geniuses I am dying!!!!!}

Reply 465

username1194172

Original post by Aimen.

Well the ideal solvent is the one in which solute dissolves most in hot solution and doesn't dissolve in cold solution at all. Since no solution is ideal, we use the solution in which most solution dissolves most in hot solution and least in cold solution, as in the one with greatest difference in the two solubility values.
So now in this case, the difference in values of solution 1 is 5 whereas in solution 2 is 7.5 and as solution 2's difference > solution 1's difference so 2 is a better solvent.
Well i hope it was a helpful explanation :smile:

why must the solvent be hot though?

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Reply 466

Jossssshhhhh

Original post by Louisss

why must the solvent be hot though?

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Is anyone here doing Chemistry AS Empa? :smile:

Hoping its not too bad as some papers have been bad!

Reply 467

A.S.J

Original post by djmans

AS or A2

Reply 468

A.S.J

Original post by djmans

guys please help
what happens if a piece if a piece of sodium is added to an alcohol

Effervescence. Bubbling.
the OH of alcohol becomes O- Na+
If only Na solid then H2(g) released.
If NaOH then H2O.
Likewise.

Reply 469

thenextchemist

Anyone got a really hard unit 5 aqa question from any of the exam papers?

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Reply 470

Glavien

Can someone help with the last part of this question please, the reaction with oxygen. Thanks!
It's from the January 2012 AQA paper.
ImageUploadedByStudent Room1462709288.608360.jpg

ImageUploadedByStudent Room1462709288.608360.jpg

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(edited 7 years ago)

Reply 471

PlayerBB

Original post by Louisss

why must the solvent be hot though?

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To dissolve the solid for recrystallisation

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Reply 472

shiney101

Can someone help me with q9? It's about percentage error, and they've said in the answer that the titre will be 24.4 so you can use that.
I've forgotten what the formulae for percentage error is ://
http://filestore.aqa.org.uk/subjects/AQA-CHM6T-P10-TEST.PDF

Thanks

Reply 473

Ishaqz01

How do you measure accurately the mass on an insoluble precipitate?

and

How can you use a more accurate end point of neutralisation reaction when an indicator is used?

Reply 474

CERC

Original post by djmans

guys please help
what happens if a piece if a piece of sodium is added to an alcohol

hi there!

according to my ccea revision guide, when sodium metal is added to say ethanol sodium ethoxide is produced and hydrogen.

2 C2H5OH + 2Na ------------2 C2H5ONa + H2

The sodium ethoxide produced belongs to a homologous series called "Alkoxides"

Reply 475

djmans

Original post by A.S.J

Effervescence. Bubbling.
the OH of alcohol becomes O- Na+
If only Na solid then H2(g) released.
If NaOH then H2O.
Likewise.

what about sodium carbonate

Reply 476

PlayerBB

Original post by djmans

what about sodium carbonate

alcohols don't react with sodium carbonate, they are slightly acidic and this won't be enough to liberate CO₂

Reply 477

Aimen.

Original post by shiney101

Well percentage error is (uncertainity or error)/total titre*100
and since this gives percentage error in each reading so when doing this for burrette we multiply uncertainity by 2 as we take two readings (initial and final)

Reply 478

Aimen.

Original post by Louisss

why must the solvent be hot though?

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You should definately watch a few videos on this if you haven't done it in labortary yourself. One i'd suggest is https://youtu.be/qJLvB6NFnoA
And you'll see that to dissolve the solute we heat the solvent x)