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Help with ionic equation chemistry

I'm really stuck with how this is the answer. I did a mock and completely guessed and and got it

"When CH3Cl is bubbled with Silver Ions and Ethanol (aq), a precipitate forms. Write an ionic equation"

My answer: Ag+ + Cl- -> AgCl (with correct state symbols

I'm confused on how this is right. I know you need to cancel out spectator ions and write out the charges but I still am confused.
Reply 1
Original post by hwhejfjejsjx
I'm really stuck with how this is the answer. I did a mock and completely guessed and and got it
"When CH3Cl is bubbled with Silver Ions and Ethanol (aq), a precipitate forms. Write an ionic equation"
My answer: Ag+ + Cl- -> AgCl (with correct state symbols
I'm confused on how this is right. I know you need to cancel out spectator ions and write out the charges but I still am confused.

Methyl chloride does not ionise to form chloride anion because the corresponding methyl carbonium ion is a high energy species. Under the influence of Ag+, one lone pair on Cl of methyl chloride donate to Ag+ and form a complex Ag-Cl(+)-Me, then the alcohol oxygen (a nucleophile) attacks the electrophilic carbon of the complex to form ethyl methyl ether (after losing a proton) and silver chloride. I do not beleive that the simple ionic equation Ag+ + Cl- > AgCl actually happened.
Reply 2
Original post by hwhejfjejsjx
I'm really stuck with how this is the answer. I did a mock and completely guessed and and got it
"When CH3Cl is bubbled with Silver Ions and Ethanol (aq), a precipitate forms. Write an ionic equation"
My answer: Ag+ + Cl- -> AgCl (with correct state symbols
I'm confused on how this is right. I know you need to cancel out spectator ions and write out the charges but I still am confused.

Which exam board are you doing?
Original post by hwhejfjejsjx
I'm really stuck with how this is the answer. I did a mock and completely guessed and and got it
"When CH3Cl is bubbled with Silver Ions and Ethanol (aq), a precipitate forms. Write an ionic equation"
My answer: Ag+ + Cl- -> AgCl (with correct state symbols
I'm confused on how this is right. I know you need to cancel out spectator ions and write out the charges but I still am confused.
As above, which exam board are you with?

If I had to hazard a guess, they’ve told you the ethanol is aqueous and so an A level answer would be that you get an SN2 reaction (this term is only needed for Edexcel - for other exam boards, this is just the standard nucleophilic substitution mechanism) with water:

CH3Cl + H2O —> CH3OH + Cl^- + H^+

Presumably this is why you have chloride ions present and so you get precipitation upon the addition of the silver ions (since AgCl is insoluble in water and ethanol).

In reality, tkms2009 is most probably correct. Whilst A level courses would expect you to look at the conditions used and think hydrolysis (edexcel explicitly says this in the specification - see point 32ii under topic 6D: halogenoalkanes), it’s more likely ethanol is acting as the nucleophile and you are getting a complex formed between the Ag^+ and chloromethane.
Original post by Pigster
Which exam board are you doing?
OCR B
Original post by tkms2009
Methyl chloride does not ionise to form chloride anion because the corresponding methyl carbonium ion is a high energy species. Under the influence of Ag+, one lone pair on Cl of methyl chloride donate to Ag+ and form a complex Ag-Cl(+)-Me, then the alcohol oxygen (a nucleophile) attacks the electrophilic carbon of the complex to form ethyl methyl ether (after losing a proton) and silver chloride. I do not beleive that the simple ionic equation Ag+ + Cl- > AgCl actually happened.

This was the answer in the mark scheme directly from OCR
(edited 2 weeks ago)
Original post by hwhejfjejsjx
This was the answer in the mark scheme directly from OCR

OCR B’s spec isn’t super clear on this particular reaction, but it should technically fall under the “The Ozone Story” part of the course.

The OCR B specification only seems to identify water, hydroxide ions and ammonia as nucleophiles you need to know the reactions of haloalkanes with (see the specification for “The Ozone Story”, under the “organic reactions” section of the topic spec point k ii).

It stands to reason that my explanation of where the chloride ions come from is what is expected as water is the only one of the three named nucleophiles that would be present in the system. If you were asked why they bothered to add ethanol, it is likely they would want you to say it’s a matter of making the chloromethane soluble in the reaction mixture - not because the ethanol acts as a nucleophile itself.

The precipitation is silver chloride, as the Ag^+ and Cl^- ions would be expected to combine to form insoluble silver chloride.
(edited 2 weeks ago)
Reply 7
Original post by UtterlyUseless69
As above, which exam board are you with?
If I had to hazard a guess, they’ve told you the ethanol is aqueous and so an A level answer would be that you get an SN2 reaction (this term is only needed for Edexcel - for other exam boards, this is just the standard nucleophilic substitution mechanism) with water:
CH3Cl + H2O —> CH3OH + Cl^- + H^+
Presumably this is why you have chloride ions present and so you get precipitation upon the addition of the silver ions (since AgCl is insoluble in water and ethanol).
In reality, tkms2009 is most probably correct. Whilst A level courses would expect you to look at the conditions used and think hydrolysis (edexcel explicitly says this in the specification - see point 32ii under topic 6D: halogenoalkanes), it’s more likely ethanol is acting as the nucleophile and you are getting a complex formed between the Ag^+ and chloromethane.

In theory, methyl chloride would undergo SN2 reacton with ethanol and water too (a weaker nucleophile), but the reaction is painfully sluggish (I do not knwo how long it will take). That's why chemists put in silver ion to activate the reaction to a reasonable rate. I wish I could insert the ChemDraw graphic here, showing the mechanistic pathway of this reaction, but I could not. This is a university second year organic chemistry problem and most of you people need not worry about it.
If you display your email address here, I will send you the ChemDraw graphic of the mechanism of this reaction.
Reply 8
Original post by tkms2009
In theory, methyl chloride would undergo SN2 reacton with ethanol and water too (a weaker nucleophile), but the reaction is painfully sluggish (I do not knwo how long it will take). That's why chemists put in silver ion to activate the reaction to a reasonable rate. I wish I could insert the ChemDraw graphic here, showing the mechanistic pathway of this reaction, but I could not. This is a university second year organic chemistry problem and most of you people need not worry about it.
If you display your email address here, I will send you the ChemDraw graphic of the mechanism of this reaction.

However, you need to have a ChemDraw programme to open my ChemDraw file.
Yeah, I don't happen to have ChemDraw (I need to talk to the IT department about that, thanks for the reminder). So instead, I cheated and used MolView and sloppily added in a few missing details with the draw function in Google docs and used snipping tool to make the image paste-able (is that even a word lol) into the post.

The result is terrible and will probably give you an aneurysm, but just to clarify, there are limitations to MolView and google docs and so the mechanism can only be drawn so well. I have shown water acting as the nucleophile for simplicity, though we both agree that ethanol is more likely to react and form the ether. The equatorial bonds in the transition state should be partial bonds, except they are drawn really sloppily and no undergrad chemist would be recommended to draw them the way I have.



As a warning to the OP, this mechanism isn't quite what A level requires - yes, you have nucleophilic substitution by a similar mechanism, but the main differences are that you wouldn't be expected to show the formation of the complex between silver ions and the haloalkane. You would, however, be expected to show lone pairs, dipoles and the loss of the extra H^+ explicitly.
(edited 2 weeks ago)
Wonderful! The mechanism shown by Utterlyuseless69 is correct. The important point of the mechanism is that naked Cl- is not present. Water is illustrated as the nucleophile in stead of ethanol and the product is methanol.
However, the major product should be ethyl methy ether because ethanol is a stronger nucleophile than water.
Reply 11
Original post by hwhejfjejsjx
I'm really stuck with how this is the answer. I did a mock and completely guessed and and got it
"When CH3Cl is bubbled with Silver Ions and Ethanol (aq), a precipitate forms. Write an ionic equation"
My answer: Ag+ + Cl- -> AgCl (with correct state symbols
I'm confused on how this is right. I know you need to cancel out spectator ions and write out the charges but I still am confused.

Hi, so tbh I don't think you need to know how to write the whole equation. I guess ethanol is just a solvent here, and you just need to know that Ag+ and Cl- give a white ppt of AgCl. Not sure if that's helpful..
Original post by Maga^_^
Hi, so tbh I don't think you need to know how to write the whole equation. I guess ethanol is just a solvent here, and you just need to know that Ag+ and Cl- give a white ppt of AgCl. Not sure if that's helpful..
You are correct- this is what A level expects. The question simply asks for an ionic equation which an A level understanding would simply be due to the formation of chloride ions, followed by their reaction with Ag^+.

Whilst tkms2009 isn’t wrong that this is a huge simplification in reality, their answer and the mechanism I illustrated it with are what would be expected at a more advanced level (i.e first or second year undergraduate).
Original post by Maga^_^
Hi, so tbh I don't think you need to know how to write the whole equation. I guess ethanol is just a solvent here, and you just need to know that Ag+ and Cl- give a white ppt of AgCl. Not sure if that's helpful..

If the reaction is simply Ag+ + Cl- in ethanol as the solvent to give AgCl, hwhejfjejsjx would not have posted it for help. This was not the best question set by the examiners because the focus of the reaction should not be on the formation of silver chloride.

Let’s talk a little more of this reaction. I am not doing this for A-level students. I am doing this for students who love chemistry and want to learn more. Students who only want to know materials within the syllabus need not read further.

The reaction is a solvolysis reaction, a nucleophilic substitution where the nucleophile (Nu) is a solvent molecule. In a general chemistry laboratory, aqueous ethanol is 96% (w/w) ethanol in water. So there are two nucleophiles here, ethanol and water (oxygen in the OH group with a lone pair is considered to be electron rich and therefore a nucleophile). When ethanol reacts as a nucleophile, the reaction is an ethanolysis and if water reacts, the reaction is a hydrolysis. Ethanol is a stronger nucleophile than water (please try to rationalize this using electronegativity). However, both ethanol and water are neutral molecules and are weak nucleophiles.

The basic requirement for an ionic organic reaction to take place is that there should be an electrophile (electron poor species) and a nucleophile (electron rich species) in the reaction medium. The nucleophile donates a pair of electrons to the electrophile and a new covalent bond is formed. The electrophile (E) here is methyl chloride. Chlorine is more electronegative than carbon and the C-Cl bond is polarized with the chloride bearing a slightly negative charge and the carbon a slightly positive charge (weak electrophile). Nucleophiles would attack the electrophilic carbon in methyl chloride. The chlorine (with lone pairs) in methyl chloride is classified as a nucleophile too.

When you mix methyl chloride (E) and ethanol (Nu) together, in theory they should react, but in reality this ethanolysis is very sluggish because both E and Nu are not strong and reactive species. One can improve the rate of the reaction by either using a more reactive E or using a more reactive Nu. In the present case, chemists used Ag+ to activate the reaction by forming a more reactive electrophile for ethanol/water to attack.

Referring to the mechanism by Utterlyuseless69, Ag+ is a strong electrophile because it is positively charged and a strong enough E to be attacked by the weak chloride (Nu) in methyl chloride. (Ethanol and water are Nu and can attack Ag+ too, but the reactions do not lead to any products). A complex is formed and we can observe the chloride is now fully positively charged and this will further polarise the C-Cl bond, thus making the carbon more electrophilic (more positively charged) and hence reactive enough to be attacked by the weak ethanol to give ethyl methyl ether as the major product. The minor product is methanol from hydrolysis of methyl chloride (shown in the mechanism by Utterlyuseless69). The by-product is silver chloride. I stand by Utterlyuseless69 mechanism that AgCl is not formed from Ag+ and Cl-.
Please feel free to ask me questions.

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