Organic Chemistry help

When forming carboxylic acids where do the hydrogens go - for example the formula for ethanol is C2H5OH whereas the formula for ethanoic acid us CH3COOH - where did 2 of the hydrogens go?

Reply 1

charco

Study Forum Helper

Original post by KhaledChouman

When forming carboxylic acids where do the hydrogens go - for example the formula for ethanol is C2H5OH whereas the formula for ethanoic acid us CH3COOH - where did 2 of the hydrogens go?

I assume you are talking about reactions.
If you look at the balanced equation you will see exactly where they "go".

Reply 2

rachellca

Original post by KhaledChouman

When forming carboxylic acids where do the hydrogens go - for example the formula for ethanol is C2H5OH whereas the formula for ethanoic acid us CH3COOH - where did 2 of the hydrogens go?

CH3CH2OH + [O] = CH3CHO +H2O (where your 2 Hs are found) If this were distilled only ethanal would be formed.
CH3CHO + [O] = CH3COOH under reflux
[O] = acidified potassiumdichromate VI

Reply 3

charco

Study Forum Helper

Original post by charco

I assume you are talking about reactions.
If you look at the balanced equation you will see exactly where they "go".

If you use dichromate(VI) ions to oxidise the ethanol then the two half equations are:

C₂H₅OH + H₂O ==>> CH₃COOH + 4H⁺ + 4e
Cr₂O₇^2- + 14H⁺ + 6e ==> 2Cr³⁺ + 7H₂O

to add the two equations together you have to first equalise the electrons by mtb 3 in equation 1 and mtb 2 in equation 2

3C₂H₅OH + 3H₂O ==>> 3CH₃COOH + 12H⁺ + 12e
2Cr₂O₇^2- + 28H⁺ + 12e ==> 4Cr³⁺ + 14H₂O
------------------------------------------------------------------ add
3C₂H₅OH + 3H₂O + 2Cr₂O₇^2- + 28H⁺ ==>> 3CH₃COOH + 12H⁺ + 4Cr³⁺ + 14H₂O

now cancel out common terms from both sides

3C₂H₅OH + 2Cr₂O₇^2- + 16H⁺ ==>> 3CH₃COOH + 4Cr³⁺ + 11H₂O

Reply 4

KhaledChouman

Original post by rachellca

CH3CH2OH + [O] = CH3CHO +H2O (where your 2 Hs are found) If this were distilled only ethanal would be formed.
CH3CHO + [O] = CH3COOH under reflux
[O] = acidified potassiumdichromate VI

I think in GCSE we skip like 4 steps 😂

Reply 5

bl0bf1sh

Original post by KhaledChouman

When forming carboxylic acids where do the hydrogens go - for example the formula for ethanol is C2H5OH whereas the formula for ethanoic acid us CH3COOH - where did 2 of the hydrogens go?

If you look at the displayed formulae, you'll see that, in ethanol, the carbon attached to the –OH is bonded to four atoms (C, 2 x H, and O) whereas in ethanoic acid this equivalent carbon is only bonded to three atoms (C, O, and another O). To have a stable electron configuration, a carbon atom usually needs to form 4 bonds, essentially so that it has 8 valence electrons. So in ethanoic acid, one of the oxygens is bonded to the carbon via a double bond. And because oxygens usually form 2 bonds, this double-bonded oxygen does not have a hydrogen attached as well.
In the reaction, two hydrogens are usually lost as part of a water molecule.