Page 101 - Chemistry ICSE Class X

Study of Acids, Bases and Salts 87
ƒ Washing soda (sodium carbonate decahydrate). Washing soda
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.
monohydrate, (Na CO H O).
2
2
3
.
dry air
.
Na CO 10H O o Na CO H O + 9H O
2
2
2
2
3
2
3
GHƀQTGUEGPEG
washing soda sodium carbonate
monohydrate
ƒ Epsom salt (magnesium sulphate heptahydrate). Epsom salt when
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.
.
dry air
MgSO 7H O(s) o MgSO H O(s) + 6H O(g)
2
4
2
2
4
GHƀQTGUEGPEG
crystals white powder
ƒ Glauber’s salt (sodium sulphate decahydrate). Glauber’s salt
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dry air
.
Na SO 10H O o Na SO (s) + 10H O(g)
2
4
2
2
2
4

Glauber’s salt GHƀQTGUEGPEG sodium sulphate
ƒ Blue vitriol (copper sulphate pentahydrate). Blue vitriol undergoes
GHƀQTGUEGPEG VQ IKXG OQPQJ[FTCVG
.
.
dry air
CuSO 5H O(s) o CuSO H O(s) + 4H O(g)
4
2
2
4
2
copper sulphate pentahydrate GHƀQTGUEGPEG copper sulphate monohydrate

Hygroscopic Substances
What are hygroscopic substances
The substances which absorb moisture (water vapour) from the atmosphere
without dissolving in it are called hygroscopic substances. Such a property
is called hygroscopy.
ƒ Hygroscopic substances are generally anhydrous solids or liquids.
ƒ Hygroscopic substances are used as drying agents for drying gases.
Example: Some typical hygroscopic substances are
Š Conc. sulphuric acid (H SO )
4
2
Š Anhydrous calcium chloride (CaCl ) Silica gel
2
Š Calcium oxide (or quicklime, CaO)
Š Silica gel
Š Phosphorus pentoxide (P O )
2
5
Š Magnesium perchlorate [Mg(ClO ) ]
4 2
Deliquescent Substances
WƵƌĞ ƐŽĚŝƵŵ ĐŚůŽƌŝĚĞ ŝƐ ŶŽƚ
What are deliquescent substances ĚĞůŝƋƵĞƐĐĞŶƚ͘ dŚĞ ĐŽŵŵĞƌĐŝĂů
Certain anhydrous or partially hydrated salts which can absorb moisture ƐĂŵƉůĞ ĐĂůůĞĚ͕ common salt͕
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ƉƌĞƐĞŶĐĞ ŽĨ ǀĞƌLJ ƐŵĂůů ƋƵĂŶƟƚLJ ŽĨ
forming a saturated solution are called deliquescent substances. This ŵĂŐŶĞƐŝƵŵ ĐŚůŽƌŝĚĞ ŝŶ ŝƚ͘
property of salts is called deliquescence.
Deliquescence is favoured by
Š Low temperature
Š High humidity
Example: Some deliquescent substances are
Š Caustic soda (Sodium hydroxide, NaOH)
Š Caustic potash (Potassium hydroxide, KOH)