perplexus.info :: Science : pH of water

pH of water (Posted on 2003-02-11)

You have a freakish friend who only drinks pure distilled water. And keeps jars of them stored up in his basement.

When you went over to visit him, he offered you a glass. To prove to you how pure his water is, he got a pH meter and measured the pH. To his surprise, the pH was not 7!

Shouldn't the pH of pure water be 7 at 25 degrees? What happened? And was the pH greater or less than 7?

Submitted by np_rt

Rating: 3.1250 (8 votes)

Solution: (Hide)

The pure water reacted with the carbon dioxide in the air and formed an acidic solution via the following reactions:
CO2 + H2O <--> H2CO3
H2CO3 --> H(+1) + HCO3(-1)
HCO3(-1) <--> H(+1) + CO3(-2)

The numbers in parentheses represent the charge on the ion. Reactions like these are why CO2 and other gases are called "dry acids." And since the solution was acidic, its pH was less than 7 (probably somewhere between 5-6).
This is similar to how acid rain is formed; which forms from sulfur dioxide and nitrogen oxides.
I know this was a bit tough and abstract but it is a science question.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
re: yes, air	K Sengupta	2023-08-11 22:46:13
Re: Solution	Frederic Ouellet	2003-09-25 19:23:10
Solution	Jack Putz	2003-07-15 08:15:54
Got it	Chaz	2003-05-03 10:01:54
re: well.....	Gamer	2003-03-08 12:19:39
well.....	troy	2003-02-20 11:38:18
re: yes, air	Kevin	2003-02-14 04:30:12
Lower PH	Kevin	2003-02-14 04:24:00
re(2): yes, ***	Cory Taylor	2003-02-12 04:49:27
re: yes, ***	levik	2003-02-11 06:20:45
yes, air	pleasance	2003-02-11 05:46:21
Air	Anoop	2003-02-11 05:35:39
hmmm	Cory Taylor	2003-02-11 03:50:14

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