3.4 Acids, Bases and Salts

• Definition of acids and bases; the pH scale and universal indicator
• Role of acids and bases in biological processes
• Reactions of acids with bases, carbonates and metals
• Types of salts and their preparation
• Behaviour of salts exposed to air: hygroscopic, deliquescent, efflorescent
• Applications of salts and their effects on the environment

• distinguish acids and bases using the universal indicator and pH chart
• explain the role of acids and bases in biological processes
• identify products of chemical reactions of acids and bases
• classify salts according to their behaviour when exposed to air
• outline applications of salts in real life situations
• advocate for the proper usage of salts in day-to-day life

“Why does an antacid tablet stop indigestion?”

“Why does salt in a shaker clog in humid weather?”

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1. Acids, bases and what they do
   40 min · 2 practice tasks · quiz
   What makes something acidic, how to measure it, and the three reactions every acid gives.
2. Salts: types, behaviour and uses
   40 min · 2 practice tasks · quiz
   What a salt actually is, how to make one, why some clog and others crumble, and where they matter.
3. Indicators from the lab and from the market
   40 min · 1 practice tasks · quiz
   Litmus, universal indicator, phenolphthalein and hibiscus juice all report acid or alkali; only universal indicator gives a pH number.
4. Strong, weak, concentrated and dilute
   40 min · 1 practice tasks · quiz
   Strength is how completely an acid ionises; concentration is how much is dissolved. Mixing the words is a safety error as well as an exam error.
5. Acids in digestion, blood and teeth
   40 min · 1 practice tasks · quiz
   Stomach hydrochloric acid, bile as a base, blood’s narrow pH band, and tooth enamel dissolved by sugar-fed bacteria.
6. Bases on the farm and on a sting
   40 min · 1 practice tasks · quiz
   Lime and wood ash raise soil pH so crops can feed; the first-aid rule is acid sting with a base, alkali sting with a weak acid.
7. Neutralisation in the lab: salt plus water
   40 min · 1 practice tasks · quiz
   Acid plus base always gives a salt and water; the ionic heart of the reaction is H+ + OH- → H2O.
8. Acid with carbonates and with metals
   40 min · 1 practice tasks · quiz
   Carbonates fizz carbon dioxide that milks limewater; metals above hydrogen give a gas that pops. Two tests, two equations, no extra water in the metal case.
9. Naming salts and the types of salt
   40 min · 1 practice tasks · quiz
   The acid gives the ending, the metal gives the first name; normal, acid, basic and double salts, with the trap that HCl has no acid salt.
10. Making copper sulphate crystals
    40 min · 1 practice tasks · quiz
    A soluble salt from an insoluble base: excess copper oxide, filter, evaporate, cool slowly — never boil dry.
11. Precipitation of insoluble salts
    40 min · 1 practice tasks · quiz
    When the salt will not dissolve, mix two soluble solutions, filter off the precipitate, wash and dry — the method that makes barium sulphate and silver chloride.
12. Salts in air, in Kenya and in the environment
    40 min · 1 practice tasks · quiz
    Efflorescent, hygroscopic and deliquescent behaviour, Magadi and fertiliser uses, and why nitrate that grows maize can suffocate fish.