Page 114 - Chemistry_Form_2

Chemistry
for Secondary Schools

Metal oxides are those compounds which contain a metal and an oxygen atom.
Examples of metal oxides include sodium oxide, Na 2 O; potassium oxide, K 2 O;
calcium oxide, CaO; magnesium oxide, MgO; and copper(II) oxide, CuO.

Hydroxides are those compounds which contain a hydroxy group ( ̶ OH). Examples

of hydroxides include calcium hydroxide, Ca(OH) 2 ; magnesium hydroxide,
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Mg(OH) 2 ; sodium hydroxide, NaOH; potassium hydroxide, KOH; and ammonium
hydroxide, NH 4 OH.

Metal carbonates are made up of a metal ion and a carbonate ion. Examples
of metal carbonates include sodium carbonate, Na 2 CO 3 ; potassium carbonate,
K 2 CO 3 ; magnesium carbonate, MgCO 3 ; and calcium carbonate, CaCO 3 .

Bases are abundant in nature. Examples of natural substances that contain bases
are ashes, banana peels, and avocado. In addition, other bases occur naturally on
land and in water bodies; such bases include soda ash (sodium carbonate), baking
soda (sodium bicarbonate) and limestone (calcium carbonate) Figure 5.6 shows
some sources of natural bases.

(a) Soda ash deposit (b) Limestone deposit

Figure 5.6: Some sources of natural bases

Many common household products such as detergents, deodorants, toothpaste,
and baking powder contain bases. These products contain synthesised bases.

Some bases are readily soluble in water, while others are not. Soluble bases are
called alkalis. An alkali is a soluble base which, when dissolved in water, forms
hydroxide ions. Therefore, all alkalis are bases, but not all bases are alkalis.
Examples of soluble and insoluble bases are shown in Table 5.3.

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