an introduction acids, bases and ph
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Basic introduction to Acids, Bases and pH for Year 9 ScienceTRANSCRIPT
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