Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

Original post by James A

Did your teacher tell you what they reckon you would pick up on the practical?

Usually all teachers do it for the Chem ISA's.

By chem Isas are you referring to Aqa? We know our overall mark and our teacher looks at the previous year grade boundaries and has some stats on a spreadsheet to predict what we require

Posted from TSR Mobile

Reply 962

Original post by JoshL123

By chem Isas are you referring to Aqa? We know our overall mark and our teacher looks at the previous year grade boundaries and has some stats on a spreadsheet to predict what we require

Posted from TSR Mobile

So you aren't doing Edexcel Chemistry?

Reply 963

BorisGlichington

13

Has anybody got a revision summary or something of all the AS organic reactions please?

Reply 964

JoshL123

Original post by James A

So you aren't doing Edexcel Chemistry?

Hahah no I am doing Edexcel Chemistry. It is just when you said ISAs it is a term associated with AQA and not Edexcel. I just got a bit confused :P

Reply 965

Original post by JoshL123

Hahah no I am doing Edexcel Chemistry. It is just when you said ISAs it is a term associated with AQA and not Edexcel. I just got a bit confused :P

Whoops

I meant ISA as in asessed practical for Edexcel,

Reply 966

JoshL123

Original post by James A

Whoops

I meant ISA as in asessed practical for Edexcel,

Haha don't worry. A lot of my friends also do that :P... I think that they are actually called PSAs :smile:

Reply 967

Original post by David Tennant

Official Revision Question Of The Day:

Azo dyes can be prepared via coupling reactions, where an Azo group is formed between the nitrogen's of two benzene groups via a triple bond.
They typically exists as red, orange or yellow...

1) Give a reason behind the range of colours found in azo dyes such as 4-hydroyazobenzene and 4-aminoazobenzene

2) Explain why some Azo dyes banned from use and explain the chemical reason behind this.

3) In organic synthesis, how can we produce azo dyes starting with benzene? List all of the conditions and reactions involved!

I'll start us of!

concentrated HNO3 ????
Benzene---> nitro-benzene ------>????------>------> etc...
concentrated H2SO4 ????
50-60 degrees [/spoiler]

It's nice to go through some applied chemistry for once!

1) To do with de-localisation of electrons in the phenyl ring? I'm not assuming we have to know this.... but what's the answer? I'm curious!

2) Banned because they break down easily?

Nitrobenzene -------> Phenylamine

You need Tin and Conc.HCL, react under reflux, followed by treatment with a base (NaOH).

Phenylamine --------> Benzene Diazoniumchloride

Sodium Nitrite, excess HCl. Keep the temperature between 0 and 10 degrees celcius.

Benzene Diazoniumchloride ---------> Azo dye (yellow)

React with Phenol, dissolved in strong base (NaOH)!

Reply 968

David Tennant

OP

Official Revision Question Of The Day (09/05/2013):

Azo dyes can be prepared via coupling reactions, where an Azo group is formed between the nitrogen's of two benzene groups via a triple bond.
They typically exists as red, orange or yellow dyes...

1) Give a reason behind the range of colours found in Azo dyes such as 4-hydroyazobenzene and 4-aminoazobenzene.

2) Explain why some Azo dyes banned from use and explain the chemical reason behind this.

3) In organic synthesis, how can we produce azo dyes starting with benzene? List all of the conditions and reactions involved!

Spoiler

Mark scheme:

Spoiler

(edited 10 years ago)

Reply 969

Original post by David Tennant

Official Revision Question Of The Day:

1) I'm taking a wild guess with this one and saying that the groups attached determine the electron density of the delocalised pi ring. Which will cause differences in resonance. When white light hits the benzene ring you get a particular frequency back of the visible light spectrum which depends on the resonance frequency, of the benzene ring.

2) Is benzene carcinogenic ?

3) no clue :tongue:

Reply 970

blossomx

Original post by David Tennant

x

1) Give a reason behind the range of colours found in Azo dyes such as 4-hydroyazobenzene and 4-aminoazobenzene.
Because of the large delocalised cloud of electrons which is spread over the whole molecule through the N=N group. This allows the molecule to absorb light in the blue region of visible light... Not really sure on this one lol.

2) Explain why some Azo dyes banned from use and explain the chemical reason behind this.
When they are broken down they form arenes which are carcinogens.
3) In organic synthesis, how can we produce azo dyes starting with benzene? List all of the conditions and reactions involved!
Benzene w/ conc HNO3 and conc H2SO4 at 55oC to form nitrobenzene. Then reduce by adding Sn and conc HCl to form phenylamine. Then add NaNO2 and conc HCl(aq) at 5oC to form phenylammonium chloride. Liberate the phenylamine by adding NaOH. Then add phenol in NaOH to form 4-hydroxyazobenzene. (Don't think that's the right name lol)

Reply 971

David Tennant

OP

Official Revision Question Of The Day (10/05/2013):

Rusting occurs when iron losses electrons, through the formation of an anodic and a cathodic region, a circuit is produced and rusting can occur upon the surface of the metal.

Complete the following by filling in the blanks:
1) Rusting is the corrosion of ___ and ___. Other metals can corrode but not rust. It is an ____ process. Rust is hydrated ____oxide. Both water and ____ (from the air) are required for rusting. Rusting is a complicated ________ process that occurs on the ____ of iron.

2) Write down the three equations associated with the rusting of iron. Combine them to form two separate equations!

3) Rust can cause great structural damage and needs to be controlled, how can we prevent rust? Name a problem with this method and suggest how we can solve this?

(edited 10 years ago)

Reply 972

Original post by LeaX

1) Give a reason behind the range of colours found in Azo dyes such as 4-hydroyazobenzene and 4-aminoazobenzene.
Because of the large delocalised cloud of electrons which is spread over the whole molecule through the N=N group. This allows the molecule to absorb light in the blue region of visible light... Not really sure on this one lol.

2) Explain why some Azo dyes banned from use and explain the chemical reason behind this.
When they are broken down they form arenes which are carcinogens.
3) In organic synthesis, how can we produce azo dyes starting with benzene? List all of the conditions and reactions involved!
Benzene w/ conc HNO3 and conc H2SO4 at 55oC to form nitrobenzene. Then reduce by adding Sn and conc HCl to form phenylamine. Then add NaNO2 and conc HCl(aq) at 5oC to form phenylammonium chloride. Liberate the phenylamine by adding NaOH. Then add phenol in NaOH to form 4-hydroxyazobenzene. (Don't think that's the right name lol)

You mean benzenediazonium chloride? There's a noticeable difference between the two!

Make sure you don't say phenylammonium chloride in the exam!

(edited 10 years ago)

Reply 973

jojo1995

Original post by David Tennant

Official Revision Question Of The Day (10/05/2013):

Rusting occurs when iron losses electrons, through the formation of an anodic and a cathodic region, a circuit is produced and rusting can occur upon the surface of the metal.

Complete the following by filling in the blanks:
1) Rusting is the corrosion of ___ and ___. Other metals can corrode but not rust. It is an ____ process. Rust is hydrated ____oxide. Both water and ____ (from the air) are required for rusting. Rusting is a complicated ________ process that occurs on the ____ of iron.

2) Write down the three equations associated with the rusting of iron. Combine them to form two separate equations!

3) Rust can cause great structural damage and needs to be controlled, how can we prevent rust? Name a problem with this method and suggest how we can solve this?

gosh ... i literally cant answer any of these questions - do they ask questions like this in the exam? :redface:

i am scared now - by the looks of things i havent been revising the right things :tongue:

Reply 974

jojo1995

Doc2.docx

does anyone know what we need to know for this syllabus point? i havent done it in school

Reply 975

Original post by David Tennant

Official Revision Question Of The Day (10/05/2013):

Complete the following by filling in the blanks:
1) Rusting is the corrosion of iron(I) and iron(II). Other metals can corrode but not rust. It is an annoying process. Rust is hydrated iron(III) oxide. Both water and oxygen (from the air) are required for rusting. Rusting is a complicated natural process that occurs on the surface of iron.

2) Write down the three equations associated with the rusting of iron. Combine them to form two separate equations!

Fe+ ----> Fe2+ + e-
Fe2+ ----> Fe3+ + e-
O₂+ 2e- ------> 2O-

Okay, I give up :frown:

3) Rust can cause great structural damage and needs to be controlled, how can we prevent rust? Name a problem with this method and suggest how we can solve this?

oooo ! :biggrin:

Erm cover it in chromium, because I think that has a high reduction potential. However this could reach the iron one day, so maybe cover the chromium layer, with a layer of zinc as it is hard to reduce this ? :smile:

Reply 976

Original post by jojo1995

Doc2.docx

does anyone know what we need to know for this syllabus point? i havent done it in school

hehe your so lazy, couldn't you just type that here :tongue:

I would guess this is more about finding new drugs, and how that the process is important (I think the importance is obvious ) :smile:

I even think there is an example in the book about the Thalidomide case?

Reply 977

jojo1995

Original post by posthumus

hehe your so lazy, couldn't you just type that here :tongue:

I would guess this is more about finding new drugs, and how that the process is important (I think the importance is obvious ) :smile:

I even think there is an example in the book about the Thalidomide case?

LOL I'm a slow typer sorry :tongue:

ahh okay thank you so much :smile:

!!

Reply 978

Original post by posthumus

Complete the following by filling in the blanks:
1) Rusting is the corrosion of iron(I) and iron(II). Other metals can corrode but not rust. It is an annoying process. Rust is hydrated iron(III) oxide. Both water and oxygen (from the air) are required for rusting. Rusting is a complicated natural process that occurs on the surface of iron.

2) Write down the three equations associated with the rusting of iron. Combine them to form two separate equations!

Fe+ ----> Fe2+ + e-
Fe2+ ----> Fe3+ + e-
O₂+ 2e- ------> 2O-

Okay, I give up :frown:

3) Rust can cause great structural damage and needs to be controlled, how can we prevent rust? Name a problem with this method and suggest how we can solve this?

oooo ! :biggrin:

Erm cover it in chromium, because I think that has a high reduction potential. However this could reach the iron one day, so maybe cover the chromium layer, with a layer of zinc as it is hard to reduce this ? :smile:

For the oxygen half equation, water is on the right hand side, so you need protons also on the left to balance it!

Don't worry about the fact that you couldn't guess the half equation, because it's given in the data booklet anyway!

Reply 979