[Frontierlandwdw]

Here's the thread for Monday's extension science C3 chem exam.... ready for post and after discussion....

Need to get a move on with practising my mole equations but been prioritsing music and had biology yesterday aswell!

[sophiekutie]

does anyone have the equation triangles for moles to mass and moles to concentration?
please help... my teacher is soooo rubbish
i neeed 48/60 for an A*

[dippers]

(Original post by sophiekutie)
does anyone have the equation triangles for moles to mass and moles to concentration?
please help... my teacher is soooo rubbish
i neeed 48/60 for an A*

Mole-concentration=mass(g)/volume(dm^3)
Mass-concentration=number of moles/volume(dm^3)

Mass-concentration(g/dm^3) = mole-concentration (mol/dm^3) x Mr

The triangle has a M(no.moles/mass) at the top and it's divided by C((concentation) x V(volume)

Why don'y you buy a revision book, I recomend CGP GSCE Chemistry Edexcel 260Science...

[sophiekutie]

Thank you!
Haha i have that book but i don't know where the triangles are in it?

CGP is awesome for science... not great for other subjects though

[lettucesoap]

good luck! I'm really nervous about esters and soaps, my mind goes kapoof whenever there's a question.
I hope it doesnt come up

[yoyox120]

Good luck everyone and as you talk of moles can you help me out with this http://www.thestudentroom.co.uk/show....php?t=2005682

[lettucesoap]

(Original post by yoyox120)
Good luck everyone and as you talk of moles can you help me out with this http://www.thestudentroom.co.uk/show....php?t=2005682

i chipped in my 2 cents on the topic.

[lorobolorolo]

Good luck everyone. I hope the mole questions go well. But what I'm really scared about is when random questions come up which we haven't revised. For example in the june 2008 past paper there was a question about why universal indicator is not useful for titrations. I never read anything about that in the cgp revision guide. Does anyone have any recommondations on how to revise for those?

[lettucesoap]

i suppose the only way to revise for those evil random questions is by past papers.
I also like to ask myself WHY something happens so I do a bit of googling for background knowledge, which occasionally helps understand why something's done a certain way (usually not mentioned in a revision guide. but apart from that i suppose the only choice is to use logic and think like a chemistry teacher

[lorobolorolo]

thanks lettucesoap ur answer was really clever. Yeah i think i need to do a bit more research.

I did some past papers and I came across two questions which I don't really know how to get the answers to. Can someone help explaining them to me.

1. When sodium carbonate solution crystallises, washing soda crystals are formed. These can be used to neutralise acids.
Write the balanced chemical equation for the reaction that takes place when sodium carbonate is used to neutralise sulphuric acid.
The answer is: Na2CO3 + S2HO4 = Na2SO4 + H2O +CO2
How do you know it makes Na2SO4

[Coveted Ul]

Because its a displacement reaction.

You wrote the equation wrong. It's supposed to be:

Na2CO3 + H2SO4 -> Na2SO4 +H2O +CO2

[Hanpew]

(Original post by lorobolorolo)
thanks lettucesoap ur answer was really clever. Yeah i think i need to do a bit more research.

I did some past papers and I came across two questions which I don't really know how to get the answers to. Can someone help explaining them to me.

1. When sodium carbonate solution crystallises, washing soda crystals are formed. These can be used to neutralise acids.
Write the balanced chemical equation for the reaction that takes place when sodium carbonate is used to neutralise sulphuric acid.
The answer is: Na2CO3 + S2HO4 = Na2SO4 + H2O +CO2
How do you know it makes Na2SO4

it takes the first part of the sodium carbonate, and the last part of the sulphuric acid

making it Sodium Sulphate (a salt)

[Coveted Ul]

Are you guys ready for the exam?

[sophiekutie]

i'm just hoping it's not got too many equations in it.... i'm struggling to learn all of the formulas and everything!
any tips!! :s

[sophiekutie]

(Original post by Coveted Ul)
Are you guys ready for the exam?

noooooo!! Lol!

[OllieGCSEs]

Just remembering 'Moles = Mass/Molar Mass' has gotten me through nearly every equation kind of question I come across! , apart from titrations, but i use a different equation for that

[Coveted Ul]

Memorize the 3 important mole formulas, and just understand how to substitute the values into the equation.

I have a feeling there's going to be a mole question and a titration question.

[zarajade]

Does anybody want to narrow down what I need to revise into subheading for me or something
I'm panicking so much about this exam as my UMS mark is so low and this exam and the c2 exams are the only chance I have to bring it up.

[Coveted Ul]

(Original post by zarajade)
Does anybody want to narrow down what I need to revise into subheading for me or something
I'm panicking so much about this exam as my UMS mark is so low and this exam and the c2 exams are the only chance I have to bring it up.

1) Memorize the 3 mole equations
2) Describe how a flame test is carried out 1. clean 2.dip in salt 3. into blue flame
3) describe how a titration is carried out 1. pipette 2. burrette 3. add phenolphthalein 4. swirl
4) Understand electrolysis of copper - remember (OIL RIG)
5) Uses of : Esters - used in flavorings, perfume (pleasant odor) & ointments.
Alcohols - used as a solvent (miscible)
6) How detergents work- remember Hydrophilic(attracted to water), Hydrophobic(attracted to oil/grease) + lowers surface tension
7) Water - why its purified - can cause illnesses
why not to waste it - water treatment costs money.
8) test for halides - Nitric acid + Silver nitrate white ppt,cream ppt, yellow ppt; Cl,Br,I respectively
9) test for sulphate - HCl + Barium chloride -> white precipitate
10) Test for carbonate - HCl -> CO2 released, test: limewater milky-cloudy
11) Test for Sulphite - HCl -> SO2 released, test: potassium dichromate (IV) paper Orange to green.
12) Quantitative - how much present is present. Qualitative - what kind of substance is present
13) Transition metals - Forms coloured compounds + good conductors of electricity
14) Sulphuric acid - Used for fertilisers & dyes

[zaeven]

For this one Na2CO3 + S2HO4 = Na2SO4 + H2O +CO2

I think you're just supposed to know the basic reactions of an acid and what they form, so you know that an acid and a metal carbonate form carbon dioxide and water, and then you just work out the salt