Question

`CH_3 OH` and HCI both dissolve in water, but the dissolved HCI conducts electricity, while the dissolved `CH_3 OH` doesn't. Why?

Answer 1

The Hydrochloric acid dissolves as ions which conduct electricity being charged particles.
The ethanal or ethyl alcohol dissolves as a molecule which does not conduct electricity lacking any charged particles.

Explanation:

The `HCl` is an ionic compound which is separated by the polar nature of water into H+ and Cl- ions. These charged particles conduct electricity.

ethyl alcohol is a covalent compound which is separated by the polar nature of water into separate molecules. These separate molecules are not charged and so do not conduct electricity.

Answer 2

Actually, it does, it just conducts electricity to a very very small extent......

Explanation:

Be careful about "black and white" statements like "this doesn't conduct electricity". In reality, a solution of methanol and water does conduct electricity, just to a MUCH lower extent than a solution of HCl in water.

HCl dissociates into `H_3O^+` and `Cl^-` ions in aqueous solutions, and it fully dissociates (which is why hydrochloric acid is a strong acid). Methanol in water also dissociates into ions,

`2CH3OH = CH_3OH_2^++ −CH_3O^-`

The self-ionisation constant of methanol will be very low, it will be only marginally different to that of water (which is about `10^(−14)`.

So the ions will be present and will conduct electricity in a methanol/water solution, it just does it to a very very small extent. But to say that they "do not conduct" electricity implies a conductivity of zero. It will not be zero, but it will be EXTREMELY small.