an introduction acids, bases and ph

ACIDS & BASESYear 9 Science 2008

What is an Acid?

• Acids produce H+ ions in aqueous solutions water

HCl H+(aq) + Cl- (aq)

• Taste sour

• Corrode metals

• React with bases to form salts and water

• Have a pH <7

• Turn Blue Litmus paper Red

Example of Acids• HCl - Hydrochloric Acid

• Stomach acid

• C6H8O7 - Citric Acid• Found in Oranges, Lemons and other

citrus fruit• HNO3 - Nitric Acid

• used to cauterise warts and in explosives, fertilisers and dyes

Acids in Everyday Life

More Acids in Everyday Life

What is a Base?

• Produce OH- ions in waterwater

• NaOH OH-(aq) + Na+ (aq)• Taste bitter, chalky• Are electrolytes• Feel soapy, slippery• React with acids to form salts and water

• Have a pH >7

• Turn Red Litmus paper Blue

Examples of Bases

• NaOH - Sodium Hydroxide• Used to manufacture soaps and detergents and

as a drain cleaner• KOH - Potassium Hydroxide

• Used to manufacture liquid soaps and fertilizers and in alkaline batteries

• NH3 – Ammonia• House hold cleaner

• Mg(OH)2 - Magnesium Hydroxide• Used in Ant-acid treatment such as Mylanta

Weak & Strong Acids and Bases

• The strength of an acid (or base) is determined by the amount of IONIZATION. (how easily it forms ions in water).

• Strong = near complete ionisation

• Weak = little ionisation

Weak & Strong Acids & Bases

• Weak Acids• Citric Acid• Vinegar (acetic

acid)

• Weak Bases• Baking soda

(sodium hydrogen carbonate)

• Sodium Carbonate

• Strong Acids• HNO3

• HCl

• Strong Bases• NaOH• CaOH

pH

• The pH scale is a way of expressing the strength of acids and bases.

• pH <7 - Acid• pH >7 – Base• pH = 7 - neutral

Measuring pH

• There are several ways to test pH• Blue litmus paper (red = acid)• Red litmus paper (blue = basic)• pH paper (multi-colored)• pH meter (7 is neutral, <7 acid, >7 base)• Universal indicator (multi-colored)• Indicators like phenolphthalein• Natural indicators like red cabbage,

radishes

References & Questions

• Textbook:• Section 2.4 pp 62-

66

• Questions p 67• 1-3, 6-14, 17 & 17,

18-20, 22, 23, 26