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 7 14

Basic[OH-]>[H+]

Acidic[H+]>[OH-] Neutral

[H+]=[OH-]

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 StudentspH = -log10 [H+]

So if:pH = 5

Then5 = -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 Webhttp://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 DrainageSeepage 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?

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

BacteriaPlants

Carp, Suckers, CatfishBass, Bluegill, CrappieSnails, Clams, MusselsMost Aquatic Animals

pH

Some organisms can tolerate a wider pH range.

State Water Resources Control Board-Citizen Monitoringhttp://www.swrcb.ca.gov/nps/docs/Ph.doc

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…