Page 85 - Chemistry ICSE Class IX

Water 73
Š Phosphorus pentoxide (P O )
2
5
Š Silica gel
Deliquescent Substances

What are deliquescent substances
Certain anhydrous or partially hydrated salts which can absorb moisture
from the air, become moist and nally dissolve in the absorbed water, WƵƌĞ ƐŽĚŝƵŵ ĐŚůŽƌŝĚĞ ŝƐ ŶŽƚ
forming a saturated solution are called deliquescent substances. This ĚĞůŝƋƵĞƐĐĞŶƚ͘ dŚĞ ĐŽŵŵĞƌĐŝĂů
property of salts is called deliquescence. ƐĂŵƉůĞ ĐĂůůĞĚ͕ common salt͕
ĂďƐŽƌďƐ ŵŽŝƐƚƵƌĞ ĚƵĞ ƚŽ ƚŚĞ
Deliquescence is favoured by ƉƌĞƐĞŶĐĞ ŽĨ ǀĞƌLJ ƐŵĂůů ƋƵĂŶƟƚLJ ŽĨ
Š Low temperature ŵĂŐŶĞƐŝƵŵ ĐŚůŽƌŝĚĞ ŝŶ ŝƚ͘
Š High humidity
Example: Some deliquescent substances are:

Š Caustic soda (Sodium hydroxide, NaOH)
Š Caustic potash (Potassium hydroxide, KOH)
Š Magnesium chloride (MgCl )
2
Š Calcium chloride (CaCl )
2
What are drying (or desiccating) agents
The substances which can remove moisture from other substances are called
drying agents (or desiccating agents).

All hygroscopic substances are drying (or desiccating) agents.
Examples:
ƒ Silica gel ƒ Phosphorus pentoxide (P O )
5
2
ƒ Quicklime (CaO) ƒ Conc. sulphuric acid (H SO ) A desiccator is used for drying
2
4
moist substances
What are dehydrating agents
The substances which can remove water present in the structure of any
compound salt are called dehydrating agents.
Conc. sulphuric acid is a strong dehydrating agent. Conc. sulphuric
acid can remove water from copper sulphate pentahydrate, and also from
sugar molecule.
.
.
CuSO 5H O + H SO (conc.) o CuSO 4 + H SO 5H O
2
4
2
2
4
2
4
copper sulphate sulphuric acid copper sulphate
crystals (blue) (white)
Soft Water and Hard Water
What do you mean by soft water
Water which forms good lather easily with soap or soap solution is called
soft water. Soft water does not contain any salt of calcium and magnesium.
ƒ Advantages of soft water.
Š Soap dissolves in soft water and form lather easily. As a result,
washing off the soap using soft water is easy and reduces the
chances of skin diseases.
Š Clothes rinsed in soft water last longer because soft water does not
contain minerals.