The pH Scale and Indicators

The pH Scale

• pH- “potency hydrogen” [H+], a measure of how acidic or basic a solution is, the concentration of H+ ions

• pH SCALE- a logarithmic scale ranging from 0 (1x100 very acidic) to 14 (1x10-14 very basic or alkaline)

• NEUTRAL- neither acidic or basic, pH of 7

pH in Our Lives

• Soil pH– pH of the soil can vary considerably, depending on the

type of rock in the area– Has a huge effect on what types of plants can grow

where– Soil pH can sometimes be altered to improve growing conditions (ex. adding compost makes soil more acidic)

• Our skin– slightly acidic (which wards off acne bacteria)– “pH balanced” does not mean 7

• Swimming pools need a pH of 7.2-7.8

• Metal toxins in soil –ex. from batteries, lead factories –ACID LEACHING (removal by neutralization)–PHYTOREMEDIATION (removal by sponges)

Indicators

• INDICATOR- a substance that has one colour in an acidic solution and a different colour in a basic, or alkaline, solution

• Some indicators:– Thymol Blue(1.2-2.81-2 drops 0.1% soln. in aq. soln) red/acid,

yellow/base– Bromphenol Blue (3.0-4.61 drop 0.1% aq. soln.) yellow/acid, blue-

violet/base– Methyl Red (4.4-6.21 drop 0.1% aq. soln.) red/acid, yellow/base

• INDICATORS: http://www.youtube.com/watch?v=6Y4Y-__ME60

• Disadvantages of indicators:–Only identifies a substance as an acid or

base, does not tell you pH–Coloured solutions are difficult to test

• Other measurements:– LITMUS PAPER- wide range pH paper, tells

you pH–pH METER- electrode attached to digital

display

• RED CABBAGE SCIENCE EXPERIMENT:– http://www.youtube.com/watch?v=Oan3AKMatkg– http://www.youtube.com/watch?v=gNYowxbsLnE– http://www.youtube.com/watch?v=ZCXVTIV-flk&f

eature=related

• ACIDS, BASES, AND PH SCALE SONG: http://www.youtube.com/watch?v=zTLiJE-j1-I&feature=related

Neutralization Reaction• In order to neutralize (have a pH of 7) an acid or

a base, we can use a neutralization reaction.

Acid + Base Salt + Water • By adding an acid to a base, the products are salt

and water. Both of which are neutral. • Warning: if you add too much acid or too much

base, the resulting substance won't be neutral!

• Practice: Complete “The pH scale” worksheet in your booklet (including the Neutralization Reaction portion at the bottom)