Can anyone answer me this question about bleach

[Lucio]

Thought it was simpler than that, thought the typical staining on a stainless steel sink was a build up of calcium carbonate (aka chalk) from the water and that the bleach reacted to form sodium carbonate + calcium hydroxide both of which are water soluble and thus get washed away.

[DDY]

Staining in kitchen sinks is probably more complex than the simple accumulation of lime scale, but it is a significant factor especially in hard water areas.

There is also soap scum, biofilms, bits of last night's lasagne or any other external contaminant to consider... tea stains, urrggh.

Sodium hypochlorite (NaOCl) is not a great limescale remover, it's great at making tea stains colourless though. Added to water it forms Na+, OH- and HOCl, the latter HOCl (hypochlorous acid) reacts with and dissolves calcium carbonates (which forms limescale), but it's a very weak acid and the ratio of HOCl to its dissociative OCl- ion depends on pH.

At pH ~8, typical of tap water, the ratio of HOCl to OCl- is about 15:85. Basically, there's hardly any HOCl from bleach that could dissolve limescale, you could use an acid to shift the pH down to get more HOCl*, but you might as well use that acid to remove the limescale to begin with!

I'm not done yet, as mentioned in my last post, sodium hypochlorite in household bleach, especially when supplied in higher concentrations (more than a few percent), is usually delivered in a deliberately basic solution (pH 9-10), e.g. with NaOH, further decreasing the proportion of HOCl - which is the point really, because HOCl decomposes at room temperature relatively quickly.

EDIT: For the love of god don't mix bleach with acid - such as in limescale removers. It produces chlorine gas!

[Peter Parker]

Thought it was simpler than that, thought the typical staining on a stainless steel sink was a build up of calcium carbonate (aka chalk) from the water and that the bleach reacted to form sodium carbonate + calcium hydroxide both of which are water soluble and thus get washed away.

As DDY said, alkali bleaches won't dissolve or break down calcium carbonate.

If you did GCSE chemistry you might remember that calcium hydroxide (aka slaked lime or limewater) is the stuff you use to test for CO2. It goes a milky white colour due to the formation of calcium carbonate (chalk, as you rightly said). Since that's the normal energetically favourable direction of the reaction, it's very unlikely to go the other way - chalk reacting to form Ca(OH)2 - that's pretty much against the laws of thermodynamics.

I found a pretty good BBC GCSE notes page about hard water, and it's bringing back my GCSE/A-level memories !
http://www.bbc.co.uk/schools/gcsebit...er/revision/1/

Since moving down south, the much worse limescale is one of the most noticeable things

[ik9000]

use bleach. clean everything. Rinse. Lots.

Later use viakal - acidic gets rid of the limescale (with suitable elbow grease). Rinse. Lots.

Same goes for toilets. Don't just use bleach - it will discolour limescale but it's still there. Alternate with using a toilet cleaner limescale remover too.

[Xlucine]

...Since that's the normal energetically favourable direction of the reaction, it's very unlikely to go the other way - chalk reacting to form Ca(OH)2 - that's pretty much against the laws of thermodynamics...

So if I go over the limescale with a blowtorch (providing heat for the CO2 to run away), it should just rinse off?

Since moving down south, the much worse limescale is one of the most noticeable things

I dunno why everyone calls southerners soft when even our water is too hard for northerners!

[Tumble]

ok I am learning here

very good input, thank you all so far

Now.. I know it doesn't remove lime scale, so I use other things for that, and my toilet bowls get cleaned with brush's too.

but I am also interested in the thick to thin bleach issue

Is thick bleach just the same but less runny? does it have a thickening agent in?

or is it more powerful that thin bleach?

If your bog is properly minging - use a half a house brick! the brick is softer than the enamel on the throne, and way harder than ANYTHING that'll cling to it

[cptwhite_uk]

Well you learn something everyday, honestly thought bleach was acidic.

[DDY]

Well you learn something everyday, honestly thought bleach was acidic.

Technically household bleach is an acid - by the definition that it has dissociated H+ ions and can donate protons. The active chemical you get in household bleach is a sodium salt (NaOCl), but in solution the important part is HOCl which is called hypochlorous acid for a reason!

Like I poorly explained above, HOCl is a weak acid, it doesn't dissociate much at typical tap water pH and even less at the alkaline pH that bleach is typically supplied.

So you're right and wrong. Right in the technical definition, but wrong because if you stick pH indicator in bleach, it will come up as alkaline.

This is mind bending stuff, acid, but alkaline at the same time? I don't get it either, but it's what I've memorised for my exams next week!

[Peter Parker]

So if I go over the limescale with a blowtorch (providing heat for the CO2 to run away), it should just rinse off?

I dunno why everyone calls southerners soft when even our water is too hard for northerners!

Sort of. That's pretty much how you make quicklime for cement... which will be useful for rebuilding your house after you've burnt it down by "cleaning" it with a blowtorch!

There's allegedly health benefits from the extra minerals in hard water too. But it doesn't half make a mess of the kettle and I really don't want chalk in my tea.

[ik9000]

Technically household bleach is an acid - by the definition that it has dissociated H+ ions and can donate protons. The active chemical you get in household bleach is a sodium salt (NaOCl), but in solution the important part is HOCl which is called hypochlorous acid for a reason!

Like I poorly explained above, HOCl is a weak acid, it doesn't dissociate much at typical tap water pH and even less at the alkaline pH that bleach is typically supplied.

So you're right and wrong. Right in the technical definition, but wrong because if you stick pH indicator in bleach, it will come up as alkaline.

This is mind bending stuff, acid, but alkaline at the same time? I don't get it either, but it's what I've memorised for my exams next week!

yes there's a name for that- chemicals that can act as acid or bases (alkalis) depending on the relative potentials of the chemicals they're mixed with. is it amphoteric? been a while since I looked at this stuff. ammonia is another one. in the presence of a strong acid it acts as a base, but mix with an alkali and it behaves as an acid.

[Corky34]

Technically household bleach is an acid...

Technically speaking what we commonly refer to as bleach isn't bleach, technically bleach or bleaching is a process.

[DDY]

Technically speaking what we commonly refer to as bleach isn't bleach, technically bleach or bleaching is a process.

Do you mean the generalisation of everything that cleans a toilet is sometimes referred to as a bleach?

What is the colloquial definition of a bleach these days?

[Corky34]

What we normally refer to as bleach is a chemical compound but technically bleach or bleaching is the process of removing colour from something and that can be done via many different processes, like putting something in direct sunlight.

[DDY]

What we normally refer to as bleach is a chemical compound but technically bleach or bleaching is the process of removing colour from something and that can be done via many different processes, like putting something in direct sunlight.

But the sodium hypochlorite in 'household bleach' does exactly that?

[Corky34]

Yes, bleach is just the common name for a variety of chemical compounds that include sodium hypochlorite (commonly), chlorine, hydrogen peroxide, etc, etc.
It's similar to how we use the common name of 'salt' to describe sodium chloride but there's loads of other types of 'salt'

[DDY]

Yes, bleach is just the common name for a variety of chemical compounds that include sodium hypochlorite (commonly), chlorine, hydrogen peroxide, etc, etc.
It's similar to how we use the common name of 'salt' to describe sodium chloride but there's loads of other types of 'salt'

I'm not quite getting your drift.

So is household bleach, which contains sodium hypochlorite, a bleach or not a bleach?

If not, what is a bleach?