CARDINALNEWMANCATHOLICSECONDARY SCHOOL
Name: ______Date: ______SNC 2D1
THE pH SCALE
Concentrated acids and bases are very hazardous. Both are highly corrosive.
However, Hydrochloric acid is also found in your stomach and baking soda is safe enough to put into food.
How can we determine how acidic or basic a substance is?
Chemists use a pH scale to represent how acidic or basic a solution is
Most acids and bases can be ranked on this scale
Very acidic solutions have a low pH value (less than 7)
Very basic solutions have a high pH value (greater than 7)
Neutral solutions such as pure water, has a pH of 7
pH – A LOGARITHMIC SCALE
The pH scale is a logarithmic scale
Every change of one unit on the scale represents a tenfold effect on the concentration of a solution
EXAMPLE
For acids, a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4 and 100 times more acidic than a solution with a pH of 5
For bases, a solution with a pH of 13 is 10 times more basic than a solution with a pH of 12 and 100 times more basic than a solution with a pH of 11
The pH is defined according to the following formula:
pH = -log10 [H+]
where the square brackets around the H+ ion represent the “concentration of Hydrogen ions in solution”
The units of concentration are mol / L or “moles per litre”
pH AND SOIL
Lime (CaO) can be added to acidic soil to make the soil more basic
The pH of soil determines its fertility
Leguminous crops prefer neutral to slightly alkaline soils (pH 7 to 10)
Corn and small grains prefer slightly acidic soils (pH 5 to 6)
Potatoes and blueberries prefer acidic soils (pH lower than 5)
Factors which affect soil acidity include organic matter decay, naturally occurring acids and acid precipitation
pH management is required to provide optimal growing conditions
pH AND COSMETICS
In many cosmetics commercials, they advertise that they are “pH balanced” – but what does this mean?
The acidity of a shampoo can have an effect on hair
Basic shampoos (high pH) causes the hair shaft to swell and push the cuticle and can eventually damage the hair, making it dry
Acidic shampoos (low pH) shampoos shrink the inner shaft and can restore the hair’s original flexibility and shine, making hair softer
Soaps with high pH can remove the slightly acidic outer layer of dead skin cells but frequent use may remove too many layers
the natural acids on the skin protect the skin from infection