Page 80 - Chemistry ICSE Class IX

68 ICSE Chemistry – 9

How to prepare an unsaturated solution of a substance
To prepare an unsaturated solution of a solute, dissolve a quantity of solute
lesser than its solubility at that temperature in the solvent.

What is a saturated solution
A solution in which no more solute can be dissolved at any xed temperature
is called a saturated solution. In other words, a solution which contains the
maximum possible amount of solute at any given temperature is called a
saturated solution.

ACTIVITY 3 Aim: dŽ ƉƌĞƉĂƌĞ ƐĂƚƵƌĂƚĞĚ ƐŽůƵƟŽŶ ŽĨ Ă ƐƵďƐƚĂŶĐĞ ŝŶ ǁĂƚĞƌ
Materials required: tĂƚĞƌ͕ ŐŝǀĞŶ ƐĂŵƉůĞ ŽĨ ƚŚĞ ƐƵďƐƚĂŶĐĞ
Apparatus required: ĞĂŬĞƌ ;ϰϬϬ ŵ>Ϳ͕ tĂƚĞƌ ďĂƚŚ͕ ^ƟƌƌĞƌ
Procedure: &ŽůůŽǁ ƚŚĞ ĨŽůůŽǁŝŶŐ ƐƚĞƉƐ͗

<ĞĞƉ ƚŚŝƐ ǁĂƚĞƌ Ăƚ ƚŚĞ ĚĞƐŝƌĞĚ ƚĞŵƉĞƌĂƚƵƌĞ ďLJ ƵƐŝŶŐ Ă ǁĂƚĞƌ ďĂƚŚ͘
ƒ dĂŬĞ ĂďŽƵƚ ϭϬϬ ŵ> ŽĨ ǁĂƚĞƌ ŝŶ Ă ďĞĂŬĞƌ͘
ƒ
ƒ ĚĚ Ă ƐŵĂůů ƋƵĂŶƟƚLJ ŽĨ ƚŚĞ ŐŝǀĞŶ ƐƵďƐƚĂŶĐĞ ŝŶƚŽ ƚŚĞ ǁĂƚĞƌ ĂŶĚ ƐƟƌ ƚŽ ĚŝƐƐŽůǀĞ ŝƚ͘
ƒ ĚĚ Ă ůŝƩůĞ ŵŽƌĞ ƐƵďƐƚĂŶĐĞ ĂŶĚ ĂŐĂŝŶ ƐƟƌ ƚŽ ĚŝƐƐŽůǀĞ ŝƚ͘
ƒ ŽŶƟŶƵĞ ĚŝƐƐŽůǀŝŶŐ ŵŽƌĞ ĂŶĚ ŵŽƌĞ ƐƵďƐƚĂŶĐĞ ƵŶƟů Ă ůŝƩůĞ ƐƵďƐƚĂŶĐĞ ŝƐ ůĞŌ ƵŶĚŝƐƐŽůǀĞĚ Ăƚ ƚŚĞ ďŽƩŽŵ ŽĨ ƚŚĞ
ďĞĂŬĞƌ͘
ƒ <ĞĞƉ ƚŚĞ ƐŽůƵƟŽŶ ƐŽ ƉƌĞƉĂƌĞĚ Ăƚ ƚŚĞ ĚĞƐŝƌĞĚ ƚĞŵƉĞƌĂƚƵƌĞ ĨŽƌ Ă ĨĞǁ ŵŝŶƵƚĞƐ͘
ƒ dŚĞ ƐƵƉĞƌŶĂƚĂŶƚ ƐŽůƵƟŽŶ ŝƐ ƐĂƚƵƌĂƚĞĚ ƐŽůƵƟŽŶ ŽĨ ƚŚĞ ŐŝǀĞŶ ƐƵďƐƚĂŶĐĞ ŝŶ ǁĂƚĞƌ Ăƚ ƚŚĂƚ ƚĞŵƉĞƌĂƚƵƌĞ͘

What is a supersaturated solution
A solution that holds more solute than its saturated solution can hold
zŽƵ ĐĂŶ ƉƌĞƉĂƌĞ ƐĂƚƵƌĂƚĞĚ ƐŽůƵƟŽŶ
ŽĨ Ă ƐƵďƐƚĂŶĐĞ ŝŶ ĂŶLJ ƐŽůǀĞŶƚ ;ŽƚŚĞƌ at that temperature is called supersaturated solution. In other words, a
ƚŚĂŶ ǁĂƚĞƌͿ ďLJ ƚŚĞ ƐĂŵĞ ŵĞƚŚŽĚ͘ /Ŷ solution which is more concentrated than a saturated solution at the same
ƐƵĐŚ Ă ĐĂƐĞ͕ ŝŶƐƚĞĂĚ ŽĨ ǁĂƚĞƌ͕ ƚĂŬĞ ƚŚĞ temperature is called supersaturated solution.
ƐŽůǀĞŶƚ ŝŶ ƚŚĞ ďĞĂŬĞƌ͘ Supersaturated solution of a solute (not for all solutes) is obtained
CAUTION: Ž ŶŽƚ ŚĞĂƚ ĂŶLJ ǀŽůĂƟůĞ by preparing a saturated solution at higher temperature and allowing it
ƐŽůǀĞŶƚ ĚŝƌĞĐƚůLJ ŽŶ ŇĂŵĞ͘
to cool undisturbed.
What is the effect of cooling on a saturated solution
In general, the solubility of a solid solute decreases with a fall in temperature
or on cooling. So, when the temperature of a saturated solution is lowered,
a part of the dissolved solute separates out in the form of crystals. The
solution in contact with these crystals is the saturated solution at the lower
temperature.

What is the effect of heating on a saturated solution
A saturated solution of a substance is saturated at a particular temperature
only. This is because the solubility of any substance has a xed value at a
particular temperature.
In general, the solubility of a solute increases with a rise in temperature
(or on heating). So, when the temperature of a saturated solution is raised,
more solute can be dissolved in it. A solution in which more solute can be
dissolved is called unsaturated solution. Therefore, when the temperature
of a saturated solution is raised, it becomes an unsaturated solution.
It may be noted that if a solution is left open at higher temperature
for long, the solvent slowly vaporises leaving behind the solid solute.