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AS Chemistry- helping each other out!

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a) think of an ammonium ion? It is dative covalent bonding a PH3 molecule is trigonal pyramidal in shape. Bond angle of 107' When a proton comes along, the PH3 will donate it's lone pair of electrons to the proton and dative covalently bonds therefore the new bond angle is 109.5, ygm?

c) The bond angle will be 90', octahedral shape

Yeah got it sound g

Reply 1141

l1lvink

Original post by Singh_0115

Anyone doing ocr A wanna help each other with course works practicals message me I've done a 2 of each so far but I'm aiming for 80% so need some help!

Posted from TSR Mobile

Please look 1 post above your's.
Many Thanks.

Reply 1142

Nautic4l

I'm having trouble finding the enthalpy change of combustion of hydrogen in my data book, I'm on Edexcel, can anyone help?

Reply 1143

kdizzle97

For Edexcel AS Chemistry are there certain practicals we need to know for the exams? I've seen the crystals one come up a few times in the past papers I've done, are there any more? :smile:

Reply 1144

S.Ahmad

Original post by jerseyalevel

For the 'Green Chemistry' topic of the Unit 2 Exam in AS OCR A, how much detail do we need to go into? Im a little lost as to whether we need to know lots of examples etc.

Thanks

The question which seems to crop up a lot over the past years has been how catalytic converters work - Absorption of CO and NO which weakens the bonds (held onto the metal surface), by the metal surface of the converter. Bonds form with the metal surface, these hold the gas molecules in the correct position for a reaction to occur. These are then Desorbed by the surface, releasing C02 and N2.

Original post by Super199

Can someone explain the displacement reactions for the halogens. Is the reason why bromine cannot displace chlorine due to chlorine being more reactive than it. Also when bromine displaces say potassium iodide do you get an orange or brown solution?

A more reactive halogen displaces a weaker halogen, that's the essential theory - this is known as a Displacement reaction as you've said. And so, Chlorine can displace both Br2 and I2, Br2 can only displace I2, whereas I2 can't displace anything as said halogens are more reactive.
Br2 + 2I- -> 2Br- + I2
To detect the presence of Iodine, in water it would be brown and in cyclohexane it would be violet.

Reply 1145

S.Ahmad

Original post by tobeobi

Can someone please give me a step by step guideline on how to predict the shapes and bond angles in molecules and ions? I find this really difficult and the book only confuses me

Okay, a bit of exam technique; Always mention the number of bonded and lone pairs.
Always mention that if a molecule only has bonded pairs the electron pair repulsion is equally and this causes the molecule to spread out as far as possible.
And always mention, lone pairs repel more than electron pairs.

This is the tedious bit, this is just a case of remembering all the different shapes and bond angles. They'll give you a molecule, it may help to draw a Dot and Cross diagram of the covalent bonds. Then, correspond the number of bonded and lone pairs to the molecule characteristics below:
Linear - 2 double bonds, bond angle of 180.
Trigonal Planar - 3 bonded pairs, bond angle of 120.
Tetrahedral - 4 bonded pairs, bond angle of 109.5.
Octahedral - 6 bonded pairs, bond angle of 90.
Pyramidal - 3 bonded pairs and 1 lone pair, bond angle of 107.
Non-linear - 2 bonded pairs and 2 lone pairs, bond angle of 104.5.

(edited 9 years ago)

Reply 1146

chantellerose

Hello!
I'm doing edexcel chemistry :smile:

Does anyone have any notes or link to videos on naming organic compounds? Or is someone able to explain it? I'm so bad at this yet everyone tells me how easy it is!

Reply 1147

KingThomas

HELP ME SOMEONE AS

HElp me with the equation

and state and explain any difference between the two spectra

Thanks

Anyone have any useful material on Ozone depletion ? and Module 4 resources in general ?

(edited 9 years ago)

Reply 1149

username1533709

Original post by chantellerose

Hello!
I'm doing edexcel chemistry :smile:

Does anyone have any notes or link to videos on naming organic compounds? Or is someone able to explain it? I'm so bad at this yet everyone tells me how easy it is!

Yes.
Here are some links for help with naming organic compounds
https://www.youtube.com/watch?v=hZpzvG9A6OM&list=PLaySzQJTCO1ljKT9Qc1J04EB7FRwZyXoT
http://www.chemguide.co.uk/basicorg/conventions/names.html

And afterwards, ypu can practice with quizzes on this link

http://www.chemguide.co.uk/basicorg/conventions/names.html

The trick with nomenclature is to practice.I also used to be horrible at nomenclature and failed my nomenclature class test.But then I did tons of organic chemistry and nomenclature, so after a while it just became second nature to me.
You MUST be good at nomenclature or else you will FAIL organic chemistry part of AS Chemistry, since alot of the questions you msut be able to draw or identify the organic compounds mentioned in the question.
Practice make sperfect.Either you conquer nomenclature or it will conquer you.

Reply 1150

Abby_W31

Ahh, this could be useful, I jsut posted another thread before i came across this one!

I'm resitting OCR F322 and am just working on some revision posters, but I can't find my notes from last year on all the different mechanisms I need to know, the only one I can remember for certain is Radical Substitution but I know there's more!

If someone could remind me of the others I'd be really grateful!

Thank you!!

Reply 1151

username1533709

Original post by Abby_W31

It is split into 4 modules
Module 1 (Basic organic chemistry concepts and hydrocarbons):
Nomenclature, Subsitution reactions,Isomers and stereoisomers,Polymers,Atom economy and Percentage Yield,Alkenes (The reactions, properties,its double bond and uses),Alkanes and everything I mentioned for alkenes apply to its except the double bond bit,Fossil fuels,Bond fission , and petroleum.

Module 2 (Alcohols,halogenoalkanes and analysis) :
Alcohol and their uses
Reactions of alcohols
Oxidising Alcohols
Esterifiication and Esters
Halogenoalkanes
Infrared spectroscopy and Mass spectroscopy

Module 3(Energy) :colone:

nthalpy Changes
Bond Enthalpies
Measuring Enthalpy Changes
Hess Law
Reaction rates and collision theory
Catalysts
Reversible reactions
Boltzmann Maxwell Distribution
Chemical equilibrium
Equilibrium and Industry
Haber process

Module 4 (Resources):
The greenhouse effect and global warming(Learn the link between the two and remember ENHANCED greenhouse effect causes global warming)
Climate change
The ozone layer
Ozone depletion
Green chemistry
Air pollution
CO2,from villain to saviour(Hint:Basically just learn CO2 uses in Industry and how its obtained as a byprodut of fermentation).
Hope this helps

Reply 1152

Abby_W31

Original post by Kadak

Substitution reactions, that's what I'm missing! Thanks :smile:

Reply 1153

username1533709

Original post by Abby_W31

Substitution reactions, that's what I'm missing! Thanks :smile:

ALso dont forget
Electrophiliac addition
Nucleophiliac addition
Hydrogenation
Addtion reactions in general

Reply 1154

Abby_W31

Original post by Kadak

ALso dont forget
Electrophiliac addition
Nucleophiliac addition
Hydrogenation
Addtion reactions in general

THey were the ones I was after, thank you!

Reply 1155

Super199

I don't get the whole bit with the colour of solution. What does that show. From the book it says something about 'the two colourless starting materials react to produce the red-brown colour of bromine'

And on the chemrevise sheet is says the free halogen is represented by the colour of solution. Which says yellow for bromine.

Really confused. Thanks :smile:

(edited 9 years ago)

Original post by KingThomas

HELP ME SOMEONE AS

HElp me with the equation

and state and explain any difference between the two spectra

Thanks

NaCO3(s) + [Acid](aq) -> Na[Acid - H](aq) + CO2(g) + H20(l)

Reply 1157

S.Ahmad

Original post by Super199

Right a query with my aqa textbook. Surely the oxidising ability if halogens decrease as you go down a group.

Also I don't get the whole bit with the colour of solution. What does that show. From the book it says something about 'the two colourless starting materials react to produce the red-brown colour of bromine'

And on the chemrevise sheet is says the free halogen is represented by the colour of solution. Which says yellow for bromine.

Really confused. Thanks :smile:

The colour of the solution at the end indicates the halogen present after a displacement reaction, for example, bromine in water is orange in colour, whereas chlorine in water is pale-green and iodine is brown.

So, the use of this ionic equation might be helpful:
Cl2 + 2Br- -> Br2 + 2Cl-, so the chlorine halogen displaces the bromide, forming chloride and bromine. The colour changes will indicate what is present essentially. The solution can either be added to Water or Cyclohexane - cyclohexane gives a more clear result as the colour changes of Br2 and I2 are very similar in water (Orange and Brown), whereas in Cyclohexane Br2 goes Orange and I2 goes Violet.

Hope that helped.

(edited 9 years ago)

Reply 1158

Super199

Original post by S.Ahmad

The colour of the solution at the end indicates the halogen present after a displacement reaction, for example, bromine in water is orange in colour, whereas chlorine in water is pale-green and iodine is brown.So, the use of this ionic equation might be helpful:Cl2 + 2Br- -> Br2 + 2Cl-, so the chlorine halogen displaces the bromide, forming chloride and bromine. The colour changes will indicate what is present essentially. The solution can either be added to Water or Cyclohexane - cyclohexane gives a more clear result as the colour changes of Br2 and I2 are very similar in water (Orange and Brown), whereas in Cyclohexane Br2 goes Orange and I2 goes Violet.Hope that helped.

the bit about the colours I don't get. When chlorine displaces bromine surely the free halogen is bromine. Which the sheet says you get a yellow solution. But you're saying something about orange/brown.

Reply 1159

S.Ahmad

Original post by Super199

That's where the sheet is wrong, the free halogen is bromine and so the colour in water and cyclohexane would be Orange. Let me try and get a picture from my textbook.

To summarise, its always the free halogen after the displacement reaction has occurred which determines the colour of the solution.

Cl2 = Pale-green in both water and cyclohexane.
Br2 = Orange in both water and cyclohexane.
I2 = Brown in water and Violet in cyclohexane.