Page 138 - Chemistry_Form_2

Chemistry
for Secondary Schools

Physical properties of salts

The physical properties of salts include their appearance in colour, texture, and
solubility.

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Physical appearance of salts
Salts appear in crystalline or powder forms and exhibit different colours
depending on their types. For example, hydrated copper(II) sulfate is a blue
crystalline salt, while sodium chloride is a white crystalline salt. Ferrous chloride
is a green crystalline salt, while calcium nitrate is a white crystalline salt. Calcium
carbonate is a white powder. Figure 5.15 shows some examples of crystalline and
powdered salts.

Hydrated copper(II) Sodium chloride Iron(II) chloride Calcium nitrate Calcium carbonate
sulfate

Figure 5.15: Crystalline and powdered salts

Solubility of salts

Solubility of a solute in a given solvent is the number of the grams of the solute
required to saturate 100 grams of solvent at a given temperature, or it is the
amount of grams or moles of a substance that dissolve in a solvent to form a
saturated solution at a given temperature. The solubility of a solute in a solvent
is not fixed but varies with temperature. Some solutes are more soluble in certain
solvents than others. For example, 40 g of sodium chloride can dissolve in 100 g

of water at 50 °C, while 80 g of potassium nitrate can dissolve in 100 g of water at
the same temperature. In this case, potassium nitrate is more soluble than sodium
chloride. Some salts such as sodium chloride and potassium nitrate are soluble
in water, while others such as calcium carbonate and lead chloride are insoluble.

The solubility behaviour of some salts is summarised in Table 5.9.

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