Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: neilep on 11/12/2006 22:09:03

Title: Boiling Water..how many times !!
Post by: neilep on 11/12/2006 22:09:03

Dearest All,

How many times can I boil the same water in my kettle and still make a nice cup of tea ?

two times ?..three times...forty seven times ?

I don't know !!..do you ?

I think I am really asking is what chemical reaction is happening upon repetitive boiling ?

Thank you.

Oh...perhaps some info on the science of kettle boiled water would be nice as well..

Title: Re: Boiling Water..how many times !!
Post by: Heliotrope on 11/12/2006 23:36:52

There is no chemical reaction when you boil water.
It just heats up and some of it turns into gas and escapes.
You can boil water as many times as you like without ill effect.
As long as you don't allow it all to vanish into steam of course.

Part of the perceived problem here is that boiling water in a kettle involves rather more than just water and heat.
There is limescale, other rubbish in the kettle, pollutants and impurities in the water, stuff sticking to the element of the kettle, what the element is made of, the type of material the kettle housing is made of, where the water originated from etc... etc...
All these things do change the water when you boil it repeatedly.
Things build up and make the water taste different.
How it tastes depends exactly on how those things I mentioned above affect the water.
So it's going to be different for every kettle and every region's water etc...

Title: Re: Boiling Water..how many times !!
Post by: neilep on 12/12/2006 00:07:55

THANK YOU very much indeed !

I do wonder why  ' they ' say use fresh water and was aware that the water itself was Ok..but I had just a soupcon of doubt !!

I would imagine it would have to take rather a lot of boilings for the limescale to have a taste effect eh ?

THANK YOU Heliotrope for explaining it to me.

Title: Re: Boiling Water..how many times !!
Post by: neilep on 12/12/2006 00:15:08

THIS GUY  (Heliotrope) PLAYS A MEAN PERCUSSION !!!!!!

Title: Re: Boiling Water..how many times !!
Post by: Karen W. on 12/12/2006 07:09:22

I was wondering about the lime build up myself. as It doesn't take that many heatings for me to notice it on the inside of my kettle as a ring also!

Title: Re: Boiling Water..how many times !!
Post by: daveshorts on 12/12/2006 14:04:08

The limescale build up is mostly because there is Calcium Bicarbonate (Calcium Hydrogen Carbonate) dissolved in the water
Ca(HCO₃)₂ this is quite soluble.
When you heat it it decomposes
Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g)

the CaCO₃ is basically limestone and is not very soluble so it deposits where it is being formed - on the element. The solution is to dissolve it with an acid occasionally.

Title: Re: Boiling Water..how many times !!
Post by: Karen W. on 12/12/2006 16:50:40

If you don't will it eventually cause your water to develop a unusual or odd taste?

Title: Re: Boiling Water..how many times !!
Post by: eric l on 12/12/2006 17:26:29

Actually, it is not the calcium carbonate that produces the odd taste, but the more soluble minerals that get attached to it.  That is also why the limescale is most often brownish, rather than white like the cliffs of Dover.

Title: Re: Boiling Water..how many times !!
Post by: chris on 12/12/2006 18:16:07

Dave - I altered your chemical reaction slightly - there was a little mistake in it...

Title: Re: Boiling Water..how many times !!
Post by: neilep on 12/12/2006 22:33:20

Quote from: daveshorts on 12/12/2006 14:04:08

The limescale build up is mostly because there is Calcium Bicarbonate (Calcium Hydrogen Carbonate) dissolved in the water
Ca(HCO₃)₂ this is quite soluble.
When you heat it it decomposes
Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g)

the CaCO₃ is basically limestone and is not very soluble so it deposits where it is being formed - on the element. The solution is to dissolve it with an acid occasionally.

THANKS For this Dave...yes..I see !!....LOL !!!!!

Title: Re: Boiling Water..how many times !!
Post by: neilep on 12/12/2006 22:34:15

Quote from: eric l on 12/12/2006 17:26:29

Actually, it is not the calcium carbonate that produces the odd taste, but the more soluble minerals that get attached to it.  That is also why the limescale is most often brownish, rather than white like the cliffs of Dover.

THANK YOU ERIC !...perhaps having tea atop the cliffs of Dover is where the best tea can be had !!

Title: Re: Boiling Water..how many times !!
Post by: neilep on 12/12/2006 22:34:52

Quote from: chris on 12/12/2006 18:16:07

Dave - I altered your chemical reaction slightly - there was a little mistake in it...

Yes, I wasn't too sure myself...glad you corrected it Chris !!...LOL

Title: Re: Boiling Water..how many times !!
Post by: Karen W. on 14/12/2006 07:31:22

LOL!!

Title: Boiling Water..how many times !!
Post by: Lucifer Sam on 07/03/2009 03:22:49

A little late joining this topic, but I have been told that you should use freshly drawn water because it has more dissolved Oxygen in it, and this helps the tea "brew". Boiling the water drives out any gases in solution.

Sounds believable, but I've no real idea if it's true.

Title: Boiling Water..how many times !!
Post by: blakestyger on 07/03/2009 15:46:59

Quote from: Lucifer Sam on 07/03/2009 03:22:49

Sounds believable, but I've no real idea if it's true.

I think it's true - Mrs blakestyger can tell instantly if I haven't put fresh water in the kettle when I make her tea, and she's not afraid to say so. [B)]