pH Scale
Recall that the pH scale typically runs from 0 to
14 (although it is possible to have a pH outside that range). The pink
region is acidic (stomach acid,
lemon juice, vinegar), the purple neutral (pure
water, saline solution) and the blue is basic
(antacids, baking soda, bleach).
0 1 2 3 4 5
6 7 8 9 10 11
12 13 14
The [H+] in solution is usually quite
small, ∴ we usually express [H+] in terms of pH. A change in one unit of pH, changes the
concentration tenfold. You should recall
this equation from grade 10 science:
pH = -log[H+]
ex. If [H+] = 1.0 x
10-7 M, what is the pH of the solution?
pH = -log [H+]
pH = -log(1.0 x 10-7)
pH = -log(1.0 x 10-7)
= 7.00*
ex. A sample of apple juice has a pH of
3.76. Calculate the hydrogen ion
concentration.
pH = -log [H+]
3.76 = -log[H+]
log[H+] = -3.76
(To remove the log, take the anti-log - it's the 10x button on your calculator - usually found as the second function on the log button.)
[H+] = 10-3.76
[H+] = 1.74 x
10-4 M*
*Tip:
There are specific rules for rounding when using log. However, let's
make life simpler and just use two decimal places, whether reporting a
pH value or [H+] value in scientific notation.
This
reading is from a pamphlet, so the order to read it is a bit odd. Read
the section between the arrows on the first page. As for the second
and third pages, they were originally like a centrefold. So, read
across the top of the second page, then the top of the third page, then
the bottom of the second page and finally the bottom of the third page.
Whew!!
pH Scale Answers:
