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EDEXCEL AS Chemistry 1,2 and 3B revision thread.

Hopefully this thread is a good idea. I post a c1, c2 or c3b question and someone else responds depending on whether they're doing that module or not.

Hopefully we can cover most topics in this thread by tomorrow.

Here's the first question. Try and type it out like this.

Unit: C1
Question: what is the chemical equation for the reaction between chlorine and water?

Reply 1

Dimez

14

2Cl2 + 2H20 ====> 4HCl + O2

Reply 2

Dimez

14

question;what is the significance of the membrane cell is the electrolysis of brine?

Reply 3

Christophicus

OP

18

jam_boy

2Cl2 + 2H20 ====> 4HCl + O2

I thought it was this;
Cl2 + H2O => HOCl + HCl

Reply 4

Magician

15

Widowmaker

I thought it was this;
Cl2 + H2O => HOCl + HCl

c'est correct

Reply 5

wacko_demon

7

hey guys wut reactions with the ( alkanes, alkenes, halogenoalkanes and alcohols) do u need to know

peace

wacko_demon

Reply 6

Magician

15

wacko_demon

hey guys wut reactions with the ( alkanes, alkenes, halogenoalkanes and alcohols) do u need to know

peace

wacko_demon

there are quite a few... check the wbateman or your syllabus for the list.

Reply 7

Dimez

14

Widowmaker

I thought it was this;
Cl2 + H2O => HOCl + HCl

yh fanx 4 dat, im glad i get it wrong now instead of in da exam

Reply 8

wacko_demon

7

aright

thanks blood

wacko_demon

Reply 9

Christophicus

OP

18

wacko_demon

hey guys wut reactions with the ( alkanes, alkenes, halogenoalkanes and alcohols) do u need to know

peace

wacko_demon

off the top of my head.

alkanes
- with oxygen
- with halogens

alkenes
- with hydrogen
- with halogens
- with hydrogen halides
- with potassium manganate solution

halogenoalkanes
- with KOH(aq)
- with ethanolic KOH solution
- with ethanolic KCN solution
- with ammonia

alcohols
- with acidified potassium dichromate(VI) solution
- with dehydrating agents
- with halogenating agents

Reply 10

Zerforax

21

does someone want to explain to me why silicon has a really high boiling point and phrosporus doesnt? even though they are next to each other..
something about silicon being macro molecular and phorsporus being simple molecular comes to mind... but its 4 marks ._.

Reply 11

Christophicus

OP

18

jam_boy

question;what is the significance of the membrane cell is the electrolysis of brine?

It separates the cell compartments during the electrolysis. I.e. it allows sodium ions to pass from the anode to the cathode compartment but does not allow the passage of hydroxide or chloride ions, thus preventing the production of sodium chlorate(I), since the the mixing of hydroxide ions and chlorine with sodium ions would produce unwanted sodium chlorate(I).

Reply 12

snmichaels

1

Widowmaker

It separates the cell compartments during the electrolysis. I.e. it allows sodium ions to pass from the anode to the cathode compartment but does not allow the passage of hydroxide or chloride ions, thus preventing the production of sodium chlorate(I), since the the mixing of hydroxide ions and chlorine with sodium ions would produce unwanted sodium chlorate(I).

And prevents hydrogen gas and chlorine gas from reacting to form HCl gas.

Reply 13

Heidi

sarforaz

does someone want to explain to me why silicon has a really high boiling point and phrosporus doesnt? even though they are next to each other..
something about silicon being macro molecular and phorsporus being simple molecular comes to mind... but its 4 marks ._.

Si is a giant covalent structure and thus has many very strong covalent bonds throughout its structure. These bonds require high energy to break and this is why Si has the highest melting point in period 3. Phosphorus is simple molecular and has very weak intramolecular forces; van der Waals which require less energy to overcome and are therefore much easier to break.

Reply 14

Heidi

This is a 5 mark question. So I need all the help I can get with this question, cos I only got 1 mark even though I thought I might get 3 or more marks for this question :frown:

Thanks in advance.

State the relative thermal stability of potassium nitrate and calcium nitrate and explain how it is related to the sizes and charges of the ions involved.

I got a mark for saying that Ca has a higher charge (+2) than K(+1)
but that's all I got correct. :frown:

Reply 15

Heidi

Describe what u would see in this reaction:

Cl2 + 2I- ===> I2 + 2Cl-

This is a 2 mark question

I put a dark brown solution and I got a mark for that, i just don't know what the other mark is for.

Reply 16

Christophicus

OP

18

Heidi

Describe what u would see in this reaction:

Cl2 + 2I- ===> I2 + 2Cl-

This is a 2 mark question

I put a dark brown solution and I got a mark for that, i just don't know what the other mark is for.

black (or slate grey) precipitate forms. This is iodine.

Reply 17

snmichaels

1

Potassium Nitrate has much higher thermal stability than calcium nitrate.

Group II nitrates become more thermally stable down the group. WHY?: the smaller metal ion has a higher charge density therefore a higher polarising power compared to the nitrate ion. The nitrate ions has a large, easily polarisable electron cloud. Calcium ion easily polarises the large anion, attracting the electrons, this distorts the shape of the anion, the lattice is easier to breakup, this encourages decomposition.

Group I nitrates have a higher thermal stability because the potassium ion is much larger than the calcium, therefore much less polarising.

You can shorten this rather easily to fit into the answer space.

Reply 18

Christophicus

OP

18

State the relative thermal stability of potassium nitrate and calcium nitrate and explain how it is related to the sizes and charges of the ions involved.

- Potassium nitrate is more thermally stable than calcium nitrate.
- The calcium ion has a nuclear charge of +2 whereas the potassium ion has a nuclear charge of +1.
- The cations both exist in the same period so the calcium ion has a smaller ionic radius than the potassium ion since it attracts electrons towards itself due to its greater charge.
- The Ca²⁺ ion therefore has a greater polarising power than the K⁺ cation.
- Therefore, the calcium ion is able to distort the electron cloud of the nitrate ion more effectively leading to easier decomposition, since less energy is required to completely break the bond.

Reply 19

snmichaels

1

Widowmaker

- Potassium nitrate is more thermally stable than calcium nitrate.
- The calcium ion has a nuclear charge of +2 whereas the potassium ion has a nuclear charge of +1.
- The cations both exist in the same period so the calcium ion has a smaller ionic radius than the potassium ion since it attracts electrons towards itself due to its greater charge.
- The Ca²⁺ ion therefore has a greater polarising power than the K⁺ cation.
- Therefore, the calcium ion is able to distort the electron cloud of the nitrate ion more effectively leading to easier decomposition, since less energy is required to completely break the bond.

Much more efficient way of answering. :top:

EDEXCEL AS Chemistry 1,2 and 3B revision thread.

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