Download Basic Water Quality - Pleasanton Unified School District

pH
What is pH?
• pH is a measure of the acidity, [H+], or
basicity (alkalinity), [OH-], of a solution.
• The scale is typically measured from 0
to 14.
• A pH value of 7 is considered to be
neutral, neither acid nor base.
pH Scale
0
14
7
Acidic
[H+]>[OH-]
Neutral
[H+]=[OH-]
Basic
[OH-]>[H+]
What is pH?
• pH is a logarithmic function. That is,
pH = -log10 [H+].
• This simply means that a change of one
pH unit represents a 10 fold change in
the acidity, e.g. pH 5 is ten times more
acidic than pH 6.
For the More Advanced Students
pH = -log10 [H+]
So if:
pH = 5
Then
5 = -log10 [H+]
-5 = log10 [H+]
10-5 = [H+] or
[H+] = 10-5 M
Measuring pH
• pH paper
• Digital meters
pH levels in our lives
Water on the Web
http://wow.nrri.umn.edu/wow/
What affects pH?
• pH can affect and be affected by atmospheric
chemistry.
– Dissolved CO2
– Other nonmetallic oxides
• pH can affect and be affected by geological
chemistry.
– Dissolved minerals
– Other sources of minerals
• Buffering capacity
– Determines the vulnerability of a system to pH
changes
Activity:
Acids, Bases and Buffers
• See handout
• Use of Probes
• SO What??
This is what…
• Acid Precipitation
• Mine tailings
• Soils have different buffering capacities
• Can exceed tolerance levels for plants and
animals
• Can corrode buildings and other
infrastructure
http://www.cleartheair.org/acidrain/
Acid Precipitation
http://pubs.usgs.gov/gip/acidrain/2.html
Acid Mine Drainage
Seepage from an historical mine tailing deposition
area. Whitewood Valley, South Dakota. USFWS photo
by Joy Gober and Scott Larson.
http://www.r6.fws.gov/contaminants/contaminants2.html
Why is pH important?
pH
Some organisms can tolerate a wider pH range.
Most Aquatic Animals
Snails, Clams, Mussels
Bass, Bluegill, Crappie
Carp, Suckers, Catfish
Plants
Bacteria
0
1
2
3
4
5
6
State Water Resources Control Board-Citizen Monitoring
http://www.swrcb.ca.gov/nps/docs/Ph.doc
7
8
9 10 11 12 13 14
German forest damaged by
acid precipitation
Germania - Effetti delle precipitazioni acide sulla foresta di Erzgebirge
(CREDIT: © WWF-Canon / Mauri Rautkari)
http://www.wwf.it/summit/photogallery.asp?P=4
More damage…