Page 78 - Chemistry ICSE Class IX

66 ICSE Chemistry – 9

Procedure:
ƒ ^Ğƚ ƚŚĞ ƌŽƵŶĚ ďŽƩŽŵ ŇĂƐŬ͕ ƚŚŝƐƚůĞ ĨƵŶŶĞů͕ ĚĞůŝǀĞƌLJ
ƚƵďĞ͕ ŐƌĂĚƵĂƚĞĚ ƚƵďĞ ĂŶĚ ƚƌŽƵŐŚ͕ ĂƐ ƐŚŽǁŶ ŝŶ
ƚŚĞ ĮŐƵƌĞ͘ ZĞĐŽƌĚ ƚŚĞ ƌŽŽŵ ƚĞŵƉĞƌĂƚƵƌĞ͘
ƒ &ŝůů ƚŚĞ ŇĂƐŬ ĂŶĚ ƚŚĞ ĚĞůŝǀĞƌLJ ƚƵďĞ ĐŽŵƉůĞƚĞůLJ
ǁŝƚŚ ƚĂƉ ǁĂƚĞƌ ;ŶĞĂƌůLJ ϭ >Ϳ͘ dŚĞƌĞ ƐŚŽƵůĚ ďĞ ŶŽ Ăŝƌ
ďƵďďůĞ ŝŶƐŝĚĞ ƚŚĞ ĂƉƉĂƌĂƚƵƐ͘
ƒ &ŝůů ƚŚĞ ŐƌĂĚƵĂƚĞĚ ƚƵďĞ ǁŝƚŚ ǁĂƚĞƌ ĂŶĚ ƉŽƐŝƟŽŶ ŝƚ
ŽǀĞƌ ƚŚĞ ŽƉĞŶ ĞŶĚ ŽĨ ƚŚĞ ĚĞůŝǀĞƌLJ ƚƵďĞ͘ ůĂŵƉ ŝƚ ŽŶ
ƚŚĞ ŝƌŽŶ ƐƚĂŶĚ͘
ƒ EŽǁ͕ ƐƚĂƌƚ ŚĞĂƟŶŐ ƚŚĞ ŇĂƐŬ͘
ƒ ůůŽǁ ƚŚĞ ďƵďďůĞƐ ;ŽĨ ƚŚĞ ĚŝƐƐŽůǀĞĚ ŐĂƐĞƐͿ ĞǀŽůǀĞĚ
ƚŽ ƉĂƐƐ ƚŚƌŽƵŐŚ ƚŚĞ ĚĞůŝǀĞƌLJ ƚƵďĞ ŝŶƚŽ ƚŚĞ ŐƌĂĚƵĂƚĞĚ
ƚƵďĞ͘
ƒ ŽůůĞĐƚ ƚŚĞ ĞǀŽůǀĞĚ ŐĂƐĞƐ ŝŶƚŽ ƚŚĞ ŐƌĂĚƵĂƚĞĚ ƚƵďĞ͘ Experiment to show that tap water contains dissolved air
(or gases)
ƒ ^ƚŽƉ ŚĞĂƟŶŐ ǁŚĞŶ ŶŽ ŵŽƌĞ ŐĂƐ ďƵďďůĞƐ ĂƌĞ
ĨŽƌŵĞĚ͘
ƒ DĞĂƐƵƌĞ ƚŚĞ ǀŽůƵŵĞ ŽĨ Ăŝƌ ;Žƌ ŐĂƐĞƐͿ ĐŽůůĞĐƚĞĚ ŝŶ ƚŚĞ ŐƌĂĚƵĂƚĞĚ ƚƵďĞ͘ dŚŝƐ ŝƐ ƚŚĞ ǀŽůƵŵĞ ŽĨ Ăŝƌ ĚŝƐƐŽůǀĞĚ ŝŶ ŽŶĞ
ůŝƚƌĞ ŽĨ ǁĂƚĞƌ Ăƚ ƌŽŽŵ ƚĞŵƉĞƌĂƚƵƌĞ͘

What is the biological significance of air dissolved in
water

Carbon dioxide and oxygen present in the air dissolve in water. Nitrogen
has very little solubility in water.

Significance of dissolved oxygen
ƒ All aquatic plants and animals use the dissolved oxygen (DO) in
water for respiration.
The aquatic plants and animals need a certain level of oxygen in water –
sh needing the highest level of oxygen in water.

Significance of dissolved carbon dioxide
ƒ Aquatic plants use dissolved carbon dioxide for the preparation of
their food by the process of photosynthesis.
ƒ Marine animals need calcium for the formation of their shells. Carbon
dioxide dissolved in water reacts with limestone to form soluble
calcium bicarbonate. This is then absorbed by the aquatic animals.

How is the concentration of a solution measured
In chemistry, most reactions are carried out in solutions. In order to perform
calculations, it is necessary to know concentrations of the solutions. The
quantity of solute dissolved in a given mass or volume of the solution or
the solvent is called concentration of the solution.
There are many ways to describe the concentration of a solution. The
simplest way to express the concentration of a solution is in terms of mass
or volume per cent of solute in solution.

Mass per cent (or per cent by mass)
The mass of solute per 100 mass units, usually the gram unit, of the solution
is called mass per cent of solute in the solution. For example, a 5% solution