[Edwina Lee (OP)]

Drains are often blocked: bath drains, basin drains, kitchen sink drain, toilet drains etc.

Different drain tend to be blocked by different things. Bath drains tend to beblocked by sediments and hair.

What principles are used to clear drains, especially chemicals.  e.g. Alum Crystals, Sodium Hydrocide  are the ones I know about.   How do these chemicals work?

I am using one that is a dark blue liquid. I am meant to dispell as much water as practicable, then pour in the liquid and leave for 5 to 10 minutes. It states that it is suitable for all metals except aluminium.   When I pour the liquid, the water in the bath drain reacts immediately forming some steam.

To my surprise, it melts the usual plastic kitchen sponge & scrub combo within about 10 seconds without smell, and it turns cotton cloths into a black char with a strong burning smell within about a second. It also produce some violet coloured liquid rather like a per Managanese solution in school chemistry.

 I do wonder what it is.

[chiralSPO]

Incompatibility with aluminum suggests sodium hydroxide to me. Sulfuric acid is another less common drain opener, which would not be compatible with aluminum and could steam on mixing with water. I know sulfuric acid reacts with sponges, but not sure what sodium hydroxide would do.

These chemicals are supposed to help by dissolving blockages. Compounds like hair (polypeptides) and grease (fat, esters) can be hydrolyzed (split into smaller molecular fragments by reacting with water). At neutral pH, this hydrolysis reaction is very slow, but at very high and very low pH the reaction can happen quite quickly. Hence use of strong acid or strong base.

NOTE: the chemical has to get to the blockage to clear it, so if the drain is *completely* blocked, it's probably best to resort to physical methods (ie call the plumber). Also, if you have used a chemical drain opener and then call a plumber, let them know about the corrosive chemical that is now also in the pipes!

[chris]

I suspect sodium hydroxide, as suggested above; caustic soda is a popular drain cleaner because it can attack protein-rich material like hairs.

[tombaker]

Chlorination is the most common method of wastewater treatment, the technological scheme of which is well established.

The composition of the resulting mixture depends on the specific characteristics of the wastewater, as a result, the toxicity of substances is reduced compared to the initial state.

[chris]

Are you sure about that? Because bleach (sodium hypochlorite) won't degrade a lot of the materials that cause drains to block in the first place.

[Bored chemist]

Are you sure about that? Because bleach (sodium hypochlorite) won't degrade a lot of the materials that cause drains to block in the first place.

It attacks fat and hair which is a good start.

[Bored chemist]

Chlorination is the most common method of wastewater treatment,

Nobody asked about wastewater treatment.
Settling followed by aerobic digestion is the commonest method of wastewater treatment.

[Edwina Lee (OP)]

I asked because I was curious about what drain clearing chemicals may be, especially the kind I have been using.
A bit of discussion about chemistry was what I was hoping for.

The chemical(s) has these properties:-
[1] burns up cotton instantly despite it is a fluid;
[2] Oxidises Iron rust Fe3O4 to Fe2O3;
[3] dissolves/react with ordinary cleaning sponge (those spongy yellow ones with a hard green layer); A small stream of violet also appears (looks just like the Manganese oxidation chemical used in school chemistry);

Would NaOH really oxidise Fe3O4 to Fe2O3?

[chiralSPO]

When you say burns up cotton, you mean the cotton actually produces a flame? (consistent with permanganate) Or just that it apparently turns to charcoal? (consistent with sulfuric acid)

Is it bright purple to start with?

It would need an oxidizing agent to go to Fe₂O₃.

Again, a mix of NaOH and NaOCl is pretty common, and is easily strong enough of an oxidizer to do this (though I don't think it would cause cotton to combust)

Does the drain opener smell like bleach or chlorine? (or something else?)

[Bored chemist]

Sulphuric acid does most of those things.
How did you come to believe that it "Oxidises Iron rust Fe3O4 to Fe2O3;"?
How do you know that it makes Fe2O3?

[Edwina Lee (OP)]

Thanks chiroSPO, the cotton turns into charcoal rather than burn with a flame, but in doing so, does NOT give out a chlorine, NOR a sulphurous smell. Nevertheless, there is some smell - may be smell of hot metal?
However, if I rub the chemical against the orange deposit in the bath with a yellow-green sponge, there is a sulphurous smell.
 

[Edwina Lee (OP)]

How did you come to believe that it "Oxidises Iron rust Fe3O4 to Fe2O3;"?
How do you know that it makes Fe2O3?

Just guessing because the black rust on my pair of pliers turned orange.