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HUGE ERROR IN CGP BOOK (A-level Chemistry) !


M.Tawofi
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MISTAKE IN CGP BOOK 

 

 

Hello guys, I wanted to let you know that I have spotted a mistake in the CGP. I cross referenced this with the official AQA Student book and also with past paper questions to confirm this mistake.

If you use the CGP method you can actually LOSE marks !

Topic: Nucleophilic Addition-Elimination Mechanisms

Exam Board: AQA 

Subject: Chemistry (A-level)

 

 

 

In the CGP book it states that the (Cl- ion) is responsible for removing the H atom from the nucleophile.

 

Screenshot 2020 02 24 at 15.01.39

(Black Box)

 

 

The real mechanism should not show this. The hydrogen should leave by itself. 

 

The screenshot below is from the official AQA textbook - which does not show the (Cl- ion) being removed.

Screenshot 2020 02 24 at 15.08.31

 

Here is a question from an AQA paper. 

 

Screenshot 2020 02 24 at 15.02.22

 

Let's see what the mark scheme says:

 

Screenshot 2020 02 24 at 15.03.04

 

As you can see, the mark scheme says you will lose the mark for writing this.  

4 Replies
omkark
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Thats mental, I wonder why they wrote the Cl-, who is responsible for it?

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M.Tawofi
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Topic: Metal-aqua ions (Hydrolysis reactions involving excess ammonia NH3)

Exam Board: AQA 

Subject: Chemistry (A-level)

 

Ok this might be a bit technical but I found something which might save you precious marks in the exam T_T 

 

First of all, we know that copper hexa aqua will react with NH3 

Reaction 1.

[Cu(H2O)6]2+ + 2NH3    -->  Cu(H20)4(OH)2 + 2NH4+

(pale blue solution)               (blue precipitate)

 

Screenshot 2020 04 16 at 22.24.59

(here is a better image of the reaction)

 

 

 

After this we can add even more NH3/ammonia (excess) and there should be a further reaction

Reaction 2.

Cu(H20)4(OH)2 + 4NH3 --> [Cu(NH4)4(H2O)2]2+  + 2H2O + 2OH-

(blue precipitate)                   (deep blue solution)

again, this is what is should look like:

 

Screenshot 2020 04 16 at 22.27.17

 

 

However, the CGP book gives this equation:

WARNING - do not use the following reaction

Screenshot 2020 04 16 at 22.29.23

 

Although this reaction might theoretically be correct, the AQA exam and also the official AQA text guide do not use this to show the reaction with excess ammonia. Hence please avoid the CGP version for this reaction so that you don't lose marks.

 

CGP books are still incredibly amazing and I prefer them over the official AQA text guides for those who are starting A-levels. However, this is something I had to share. 

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M.Tawofi
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Here is another one:

Exam Board: AQA 

Subject: Chemistry (A-level)

Topic: Electrophilic Substitution of Benzene - Friedel Crafts (Acylation) 

 

CGP might not be technically wrong. However, the official AQA Student book and exam papers have different mechanisms.

 

 

the first part is about formation of the acyl ion;

 

CGP says:

 

Screenshot 2020 08 04 at 15.07.53

 

However, in the exam you don't have to actually draw the curly arrows from Cl to the AlCl3 (Halogen carrier).

 

Mark scheme from exam question and AQA student book says: 

Screenshot 2020 08 04 at 15.09.09

 

 

 

 

 

the second deviation by the CGP book is the electrophilic substitution mechanism. 

 

 

CGP says:

Screenshot 2020 08 04 at 15.08.10

 

(this shows the halogen carrier in the mechanism) - however you don't need to draw this:

 

 

Mark Scheme and AQA student book shows this:

Screenshot 2020 08 04 at 15.10.19
Screenshot 2020 08 04 at 15.09.23

 

neither of these show the halogen carrier.

 

 

Use the AQA version and the mark scheme for this mechanism.

 

No discredit to CGP intended - they are still amazing books!

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Cofs
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 Cofs
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CGP are scared of this man.

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