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 Form 1 Chemistry: Acids, bases and indicators online lessons

Chemical and physical properties of bases

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Answer Text:
Properties of bases.
- Bases are substances that release hydroxyl ions when added to water;
- Soluble bases are called alkalis;
Sodium hydroxide + Water → Sodium ions + hydroxyl
(a). Physical properties of bases
1. They are bitter to taste;
2. They are slippery or soapy
to feel;
3. They turn litmus blue;
4. They conduct electricity / electric current. This is because when they are added to water they release hydroxyl ions which are the ones that conduct electricity;
(b). Chemical properties.
1. Reaction with acids.
- They react with acids to form a salt and water as the only products;
- This is a neutralization reaction; and is used to cure indigestion;
- Actal tablets contain a base that neutralizes the stomach acid.
2. They precipitate some metal hydroxides.
- Addition of some alkalis to salt solutions results in formation of solids;
- Most of these are normally hydroxides;
- A solid that is formed when two solutions are mixed is called a precipitate;
- Copper (II) sulphate + Sodium hydroxide → Copper (II) hydroxide +
Sodium sulphate solution; Blue solid;
3. Effects of heat.
- Most metal hydroxides are decomposed by heat to form their oxides and water;
General equation:
Metal hydroxide#overset (heat) (to) # Metal oxide + Water; Heat
Zinc hydroxide → Zinc oxide + water