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AS Chemistry- helping each other out!

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Reply 2080
bump diddy bump bump
Original post by Dinaa
Hai der :ahee:

The effect of light on Silver Nitrates:

The precipitates, except AgI(s), darken in sunlight forming silver. This reaction is used in photography to form the dark bits on photographic film.

OK but questions:

WHY do they darken in sunlight?
Is there an equation for this?
Why can't AgI(s) darken?

curious :mmm:


They decompose to leave Ag (s)
I googled before and it said it darkens but my teacher said no lol

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Reply 2082
Original post by C0balt
They decompose to leave Ag (s)
I googled before and it said it darkens but my teacher said no lol

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Why would your teacher say that?

It does darken right?

And lol ofc that makes sense! Thanks :smile:
Original post by Dinaa
Why would your teacher say that?

It does darken right?

And lol ofc that makes sense! Thanks :smile:


Idk he said AgI doesn't darken :dontknow:

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Reply 2084
Original post by C0balt
Idk he said AgI doesn't darken :dontknow:

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Yeah it doesn't :tongue:

I was asking why it doesn't :wink:
Original post by Dinaa
Yeah it doesn't :tongue:

I was asking why it doesn't :wink:


I don't know
I googled and Wikipedia had equation of photodecposition of AgI lol

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Reply 2086
Original post by C0balt
I don't know
I googled and Wikipedia had equation of photodecposition of AgI lol

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Oh, I guess it's something I don't need to know hah :angelblush:

Thanks though b :hugs:
Reply 2087
Magnesium and Berylium react with H2SO4 to produce MgSO4 + H2, but
Calcium, Strontium and Barium with Dilute H2SO4, is a little more complicated.

Is this what happens or what you'd say happens:

Calcium, Strontium and Barium Sulphates are thought to be insoluble, hence a layer of insoluble sulphate will form, causing the reaction to slow down or stop completely.

So, does these group 2 elements not react with Dilute H2SO4?

It would produce a white precipitate and H2 bubbles.
What is the equation for the reaction?

Thank you
Original post by Dinaa
Magnesium and Berylium react with H2SO4 to produce MgSO4 + H2, but
Calcium, Strontium and Barium with Dilute H2SO4, is a little more complicated.

Is this what happens or what you'd say happens:

Calcium, Strontium and Barium Sulphates are thought to be insoluble, hence a layer of insoluble sulphate will form, causing the reaction to slow down or stop completely.

So, does these group 2 elements not react with Dilute H2SO4?

It would produce a white precipitate and H2 bubbles.
What is the equation for the reaction?

Thank you


It reacts initially but it stops
Ba(s)+H2SO4(aq)--->BaSO4(s)+H2
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Can someone explain this question and answer to me? its about enthalpy and calorimetry. "Give reason, other than hear loss, why the value obtained from student's results are less exothermic than a data book value?" The answer is incomplete combustion but why?
Less energy is released when co or c are made instead of co2 (aka incomplete combustion) so if less energy is released this will make the enthalpy value less exo
nm
Original post by black321
Less energy is released when co or c are made instead of co2 (aka incomplete combustion) so if less energy is released this will make the enthalpy value less exo


Original post by logicmaryam
Can someone explain this question and answer to me? its about enthalpy and calorimetry. "Give reason, other than hear loss, why the value obtained from student's results are less exothermic than a data book value?" The answer is incomplete combustion but why?
Reply 2092
Original post by logicmaryam
Can someone explain this question and answer to me? its about enthalpy and calorimetry. "Give reason, other than hear loss, why the value obtained from student's results are less exothermic than a data book value?" The answer is incomplete combustion but why?


Hi :smile:

Incomplete combustion will lead to soot, carbon monoxide and water.
It is less exothermic than complete combustion, due to less heat energy being emitted.
(edited 8 years ago)
Reply 2093
Original post by logicmaryam
Can someone explain this question and answer to me? its about enthalpy and calorimetry. "Give reason, other than hear loss, why the value obtained from student's results are less exothermic than a data book value?" The answer is incomplete combustion but why?


The values in the book are average/mean values. Whereas the values attained by the student are under specific conditions.
Reply 2094
Could somebody tell me what it would mean if a cream precipitate forms, and then dissolves when nitric acid is added? I understand that nitric acid removes carbonate ions, but i was under the impression that carbonate ions form a white precipitate? Thanks!
When you heat under reflux is it a open or closed top?


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Original post by Supermanxxxxxx
When you heat under reflux is it a open or closed top?


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Open

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Original post by jadys10
Anyone have any tips on good ways to revise chemistry? I'm really struggling. Plain reading the book isn't working and with making notes I tend to waste a lot of time getting it all neat and pretty and end up not getting much in my head, plus it's really quite late stage to be making notes now. I also didn't want to do papers till later because there aren't many so I want to save them. What do I do???

Spoiler



It's ok, this is me in Chemistry and Physics...sigh. What I've learnt that's working for me is to use the specification as a checklist. Literally, it tells you things to expect- what definitions you need to learn as only certain things you will be asked on. On Physics maths tutor- he has a page with past papers listed by the contents which helped me as after going over a chapter of for example moles- I found past paper questions only on moles from 2009-2013. So you're still doing the past papers, only by content each. I literally have so much to learn and probably wouldn't finish everything due to Physics as Physics right now :'( it's sad. But if worst coms to worst- there are also notes you can use on Physics maths tutor for Chemistry or anywhere. Then watch videos to understand the content. This seems to be going ok so far for me but everything at the moment is taking too much time lol. Don't worry, I'm sure I'm in a worse position that you x
Reply 2098
Original post by jadys10
Anyone have any tips on good ways to revise chemistry? I'm really struggling. Plain reading the book isn't working and with making notes I tend to waste a lot of time getting it all neat and pretty and end up not getting much in my head, plus it's really quite late stage to be making notes now. I also didn't want to do papers till later because there aren't many so I want to save them. What do I do???

Spoiler



Type/write notes in your own words. Then do every single past paper.

Make a Microsoft Excel document with all of your exam marks, and have a column for each chapter, where you can add notes for things you do not understand. It really helps.

Like this:

Original post by johnnypong
You can use the papers from the old A level to revise too. Most of the syllabus is the same...just a few tweaks that you can ignore (eg Friedel-Crafts methylation of a benzene ring). The papers are arranged differently, but the questions are very similar.

try this site...

http://pastpapers.org/chemistry-as-papers

Thanks for the link :smile:
But honestly, if someone purely used past papers without learning or reading the content from the book- what grade could they receive as these questions seem almost recycled. Say if I did 20 past papers- could I get maybe grade B through only doing that and looking at mark schemes?

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