I am new to the subject of Chemistry and have a couple of basic questions regarding pH.?

Question

Firstly, why would you never obtain an exact pH 7 value following dilution of acid or base to a concentration of 10-7 mol dm-3? Is it something to do with acid dissociation? why?

Secondly, I have measured the pH of both tap water and distilled water with a pH meter and need to explain why they are not the same. Although I am aware that tap water contains substances such as chloride and fluoride and that distilled water is pure, please could someone explain further.

Thankyou!!

Answer 1

Even recently distilled water often does not have a pH of 7.0 Water can react with the gases in the atmosphere to change the pH (These usually make the water more acidic -- lower the pH).

Tap water, in addition contains not only the chemicals added to it during the purification process, but also the original minerals that were dissolved in it (These often make the water more basic -- raise the pH)>

Answer 2

Buffering systems theories cover both your questions. The best coverage will be found in an analytical chemistry textbook.

Carbonates, hydroxides and bicarbonates alter pH in tap water. Chlorides, etc. don't have much influence.

Answer 3

a million) [H+] = 0.0015, enter that into your calculator and press . the respond is -2.80 2. pH = -Log[H+], so press <+/->. the respond is two.80 2. Acidic pH's are a million.00 - 7.00, common pH's are 7.00 - 14.00, and pH = 7.00 is unbiased. 2) [H+] = 5.0 x 10^-9, so enter 5.0 into your calculator, press , enter 9, press <+/->, and press . the respond is -8.3. pH = -Log[H+], so press <+/->. the respond is 8.3 Our calculators could selection. EE on mine capacity convert to expnential notation. as quickly as you enter the exponent, you need to interchange the sign of the exponent from + to -. as quickly as you get the Log, you decrease lower back ought to interchange the sign from + to -.