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Edexcel Chemistry Unit 1 (23/05/2013)

Does anybody know what diagrams of experiments we need to know? - the ones that we have to draw

We need to know how to draw the apparatus for:
Fractional distillation
simples distillation
Heat to reflux
Collecting a gas over water and in a gas syringe (for measuring rates of reaction).
Specific experiments? The electrolysis of copper chromate was on a past paper. Then there was also the determining of the enthalpy change using the spirit burner but with that one they didn't ask you to draw it.
I think that that's it.

Reply 61

amber206

7

Original post by Pirateprincess

We need to know how to draw the apparatus for:
Fractional distillation
simples distillation
Heat to reflux
Collecting a gas over water and in a gas syringe (for measuring rates of reaction).
Specific experiments? The electrolysis of copper chromate was on a past paper. Then there was also the determining of the enthalpy change using the spirit burner but with that one they didn't ask you to draw it.
I think that that's it.

Is fractional distillation the one with the Al2O3 catalyst and where 'suck-back' is a hazard?

Reply 62

xstarsx67

hey im kinda stuck on a really simple thing, so if someone could kindly help me i would be grateful!
Basically if Reaction 1 has a enthalpy change of -50kjmol and Reaction 2 has an enthalpy change of -233kjmol, which reaction is more likely to occur? and could you please explain why that is. thank you! :smile:

Reply 63

amber206

7

Original post by xstarsx67

hey im kinda stuck on a really simple thing, so if someone could kindly help me i would be grateful!
Basically if Reaction 1 has a enthalpy change of -50kjmol and Reaction 2 has an enthalpy change of -233kjmol, which reaction is more likely to occur? and could you please explain why that is. thank you! :smile:

I think reaction 2, as it's more energetically favourable, as it is more exothermic.

Someone correct me on this if I'm wrong?

Reply 64

TheKingOfTSR

13

Original post by xstarsx67

hey im kinda stuck on a really simple thing, so if someone could kindly help me i would be grateful!
Basically if Reaction 1 has a enthalpy change of -50kjmol and Reaction 2 has an enthalpy change of -233kjmol, which reaction is more likely to occur? and could you please explain why that is. thank you! :smile:

The more negative the enthalpy change the more energetically unstable a reaction is.
Any system like to be as stable as possible likes to have less energy as possible. That's a law of nature :cool:

Reply 65

xstarsx67

Original post by amber206

I think reaction 2, as it's more energetically favourable, as it is more exothermic.

Someone correct me on this if I'm wrong?

No that defiantly makes sense, thanks!

Posted from TSR Mobile

Reply 66

xstarsx67

Original post by TheKingOfTSR

The more negative the enthalpy change the more energetically unstable a reaction is.
Any system like to be as stable as possible likes to have less energy as possible. That's a law of nature :cool:

Oh I see, thank you for sharing your knowledge :wink:

Posted from TSR Mobile

Reply 67

kimmykim1

hi , in jan 2010 ques 5 i would have chosen C because in mean bond enthalpy were supposed to break all bonds but the answer is A, why is that?

Reply 68

posthumus

20

Original post by kimmykim1

hi , in jan 2010 ques 5 i would have chosen C because in mean bond enthalpy were supposed to break all bonds but the answer is A, why is that?

The bond enthalpy you get for the reactions other than A is for 4 C-H bonds (in CH4)... you would like the mean bond enthalpy of just one C-H bond so you divide by 4

Reply 69

Kurraiyo

7

Can someone please help me with this question? January 2012 MCQ question 3:
The definition of the mole is :

A the amount of any substance which occupies a volume of 24 dm^3 at RTP
B the amount of any substance containing the same number of identical entities (??) as there are in exactly 12 g of the carbon-12 isotope.
C the number of atoms in exactly 12 g of the carbon-12 isotope
D the number of molecules in exactly 2 g of hydrogen at RTP

The correct answer is B. I don't understand why C is wrong? Can someone PLEASE explain this :frown:

Reply 70

posthumus

20

Original post by Kurraiyo

Can someone please help me with this question? January 2012 MCQ question 3:
The definition of the mole is :

A the amount of any substance which occupies a volume of 24 dm^3 at RTP
B the amount of any substance containing the same number of identical entities (??) as there are in exactly 12 g of the carbon-12 isotope.
C the number of atoms in exactly 12 g of the carbon-12 isotope
D the number of molecules in exactly 2 g of hydrogen at RTP

The correct answer is B. I don't understand why C is wrong? Can someone PLEASE explain this :frown:

I don't have a clue exactly what B says either. But C tricked me also .... the number of atoms would be found by doing mole x Avogadro constant :tongue:

The number (or coefficient) doesn't represent the number of atoms - that's a really sneaky question.

Reply 71

kimmykim1

what is stereoisomerism ?

Reply 72

Kurraiyo

7

Original post by kimmykim1

what is stereoisomerism ?

Stereoisomerism is when the molecules have the same molecular formula but a different three dimensional arrangement in space. It arises in molecules with restricted rotation, eg the restricted rotation about the carbon-carbon double bond in alkenes. :smile:

Reply 73

posthumus

20

Original post by kimmykim1

what is stereoisomerism ?

There's 2 types... in Unit 1 you'll only need to know about Geometric isomers :smile:

They usually consist of double bonds... and the idea is that since groups can not rotate around this double bond you can get different isomers.

Here's an example:

If the bond in the "middle" was a single bond... this wouldn't have been a problem since the CH3 and H can rotate around it. Here that's not the case due to the double bond.

In the image the cis trans systems has been used.... cis means that the same elements are on the same side of the double bond (hope that makes sense :tongue:

). trans is the opposite of that as you can see.

But the E Z system is much better as in some cases you will get more than 2 types of groups. In this case "E" prefix would mean that the high priority groups/elements are on opposite sides of the double bond (equivalent to trans). "Z" is the opposite..equivalent to cis.

2 "priority" groups/atoms are chosen based on their relative atomic mass... the 2 with the greatest mass will be prioritized.

Reply 74

kimmykim1

Original post by Kurraiyo

Stereoisomerism is when the molecules have the same molecular formula but a different three dimensional arrangement in space. It arises in molecules with restricted rotation, eg the restricted rotation about the carbon-carbon double bond in alkenes. :smile:

thanks

Reply 75

ayat94

can anybody help me with ppm what is the method to handle question like this in the exam

Reply 76

Urban Ace

Hi there! Would anyone be so kind to explain the concepts of the arrows when drawing hess cycles? :redface:

Reply 77

Urban Ace

Original post by ayat94

can anybody help me with ppm what is the method to handle question like this in the exam

Well the idea with PPM (which is used for tiny amounts) is that say Xenon which makes up only 0.000009 % of the atmosphere has 0.000009 parts per 100 parts of air --> 0.000009 x 10000 = 0.09 --> 0.09 parts per million.

Reply 78

ZeshanGriffin

d you think this paper is gonna be tricky, i say that because the physics unit 1, was EXTREMELY HARD, and the biology was tricky. soo ?

Reply 79

Mollymod

15

Original post by ZeshanGriffin

d you think this paper is gonna be tricky, i say that because the physics unit 1, was EXTREMELY HARD, and the biology was tricky. soo ?

No point trying to figure out whether it'll be 'hard' or not.
It's about trying to do as well as you can so you're on the right side of the bell-curve, because that's how they sort out the boundaries, so try your best, and try to be as calm as possible. It'll all be done with in the morning, so try and revise a lot tonight, get a good night's sleep and you'll be fine in the morning. :smile:

Just try your best and don't get stressed over the difficulty. Trickiness is relative, there will always be the people who complain, yet do well and didn't actually find it hard, and the people who complain regardless of the difficulty; the best thing you can do is prepare yourself. They set boundaries to the aptitude of the candidates with regards to that paper, so if it's 'tricky' but lots of people do really well anyway, the boundaries will still be medium relative to the amount of people who succeed.
You just have to try your best to cover all of Unit 1 as comprehensively as possible, so you're prepared with some revision.

Edexcel Chemistry Unit 1 (23/05/2013)

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