Page 77 - Chemistry ICSE Class IX

Water Aim: To show that water we drink (i.e. tap water) contains dissolved solids 65

ACTIVITY 1 Materials required: dĂƉ ǁĂƚĞƌ

Apparatus required: tĂƚĐŚ ŐůĂƐƐ͕ ĞĂŬĞƌ ;ϰϬϬ ŵ>Ϳ
Procedure: &ŽůůŽǁ ƚŚĞ ĨŽůůŽǁŝŶŐ ƐƚĞƉƐ͗

ƒ
ƒ &ŝůů Ă ϰϬϬ ŵ> ďĞĂŬĞƌ ƚŽ ŝƚƐ ŚĂůĨ ǁŝƚŚ ƚĂƉ ǁĂƚĞƌ͘
WůĂĐĞ ƚŚŝƐ ďĞĂŬĞƌ ŽŶ Ă ƚƌŝƉŽĚ ƐƚĂŶĚ ǁŝƚŚ Ă ǁŝƌĞ ŐĂƵŐĞ͘
ƒ WůĂĐĞ Ă ĐůĞĂŶ ǁĂƚĐŚ ŐůĂƐƐ ŽǀĞƌ ƚŚĞ ďĞĂŬĞƌ ĐŽŶƚĂŝŶŝŶŐ ǁĂƚĞƌ͘
ƒ WŽƵƌ Ă ƐŵĂůů ƋƵĂŶƟƚLJ ŽĨ ƚĂƉ ǁĂƚĞƌ ŽŶ ƚŚĞ ǁĂƚĐŚ ŐůĂƐƐ͘
ƒ ,ĞĂƚ ƚŚĞ ǁĂƚĞƌ ŝŶ ƚŚĞ ďĞĂŬĞƌ ƚŽ ďŽŝůŝŶŐ ĂŶĚ ĂůůŽǁ ƚŚĞ ǁĂƚĞƌ ŽŶ ƚŚĞ
ǁĂƚĐŚ ŐůĂƐƐ ƚŽ ǀĂƉŽƌŝƐĞ͘ (a) The set-up to show that tap water
contains dissolved salts (b) The residue left on
ƒ tŚĞŶ Ăůů ƚŚĞ ǁĂƚĞƌ ŽŶ ƚŚĞ ǁĂƚĐŚ ŐůĂƐƐ ŚĂƐ ǀĂƉŽƌŝƐĞĚ͕ ƐƚŽƉ ŚĞĂƟŶŐ͘
the watch glass
ƒ ZĞŵŽǀĞ ǁĂƚĐŚ ŐůĂƐƐ ĨƌŽŵ ƚŚĞ ďĞĂŬĞƌ ĂŶĚ ĂůůŽǁ ŝƚ ƚŽ ĐŽŽů͘
ƒ KďƐĞƌǀĞ ƚŚĞ ƐƵƌĨĂĐĞ ŽĨ ƚŚĞ ǁĂƚĐŚ ŐůĂƐƐ ĂŐĂŝŶƐƚ ůŝŐŚƚ ĂŶĚ ŶŽƚĞ ĚŽǁŶ LJŽƵƌ ŽďƐĞƌǀĂƟŽŶ͘
ObserǀaƟon: KŶ ůŽŽŬŝŶŐ Ăƚ ƚŚĞ ǁĂƚĐŚ ŐůĂƐƐ ĂŐĂŝŶƐƚ ůŝŐŚƚ͕ Ă ĨĞǁ ĐŽŶĐĞŶƚƌŝĐ ƌŝŶŐƐ ŽĨ ƐŽŵĞ ǁŚŝƟƐŚ ƐŽůŝĚ ŵĂƚĞƌŝĂů ĂƌĞ ƐĞĞŶ͘
Results: dŚĞ ƌĞƐŝĚƵĞ ůĞŌ ŽŶ ƚŚĞ ǁĂƚĐŚ ŐůĂƐƐ ŝŶĚŝĐĂƚĞƐ ƚŚĂƚ ƚŚĞ ƚĂƉ ǁĂƚĞƌ ĐŽŶƚĂŝŶĞĚ ƐŽŵĞ ĚŝƐƐŽůǀĞĚ ƐŽůŝĚ;ƐͿ͘

What are the advantages of the dissolved salts in water

Water is a remarkable solvent. It can dissolve a wide variety of substances
in it to form solutions. Such solutions are called aqueous solutions.
ͻഩ ŝƐƟůůĞĚ ǁĂƚĞƌ ĚŽĞƐ ŶŽƚ ĐŽŶƚĂŝŶ
Water which occur in the underground reservoirs contains many salts ĚŝƐƐŽůǀĞĚ ŵŝŶĞƌĂůƐͬƐĂůƚƐ͘
and minerals both desirable and undesirable for human consumption. Such dŚĞƌĞĨŽƌĞ͕ ŝƚ ŝƐ ƚĂƐƚĞůĞƐƐ͘
salts and minerals, when present in smaller quantities, are useful for both ͻഩ ZĂŝŶǁĂƚĞƌ ĂůƐŽ ĚŽĞƐ ŶŽƚ ĐŽŶƚĂŝŶ
plants and humans. Some advantages of the dissolved salts present in water ĚŝƐƐŽůǀĞĚ ŵŝŶĞƌĂůƐͬƐĂůƚƐ͘ ,ŽǁĞǀĞƌ͕
are: ŝƚ ĚŝƐƐŽůǀĞƐ ĐĂƌďŽŶ ĚŝŽdžŝĚĞ
ŐĂƐ ǁŚŝůĞ ƉĂƐƐŝŶŐ ƚŚƌŽƵŐŚ ƚŚĞ
ƒ Salts and minerals act as plant nutrients and help plants for healthy ĂƚŵŽƐƉŚĞƌĞ͘
growth.

ƒ Certain minerals add taste to water.
ƒ The dissolved salts/minerals in water act as essential supplement
needed by our bodies to stay healthy.

Air Dissolved in Water and its Biological Importance

Air contains oxygen, nitrogen, carbon dioxide and noble gases.
ƒ Noble gases are almost insoluble in water.
ƒ Carbon dioxide has the highest solubility (out of these gases) in water.
ƒ Oxygen dissolves in water to an extent of 15 ppm at 0°C (9 ppm at
20°C).

ACTIVITY 2 Materials required: dĂƉ ǁĂƚĞƌ
Aim: To show that the tap water contains dissolved air
Apparatus required: ZŽƵŶĚ ďŽƩŽŵ ŇĂƐŬ ;Ϯ > ĐĂƉĂĐŝƚLJͿ͕ ƚŚŝƐƚůĞ ĨƵŶŶĞů͕ ĚĞůŝǀĞƌLJ ƚƵďĞ͕ ƚƌŽƵŐŚ͕ ŐƌĂĚƵĂƚĞĚ ƚƵďĞ͕ ŝƌŽŶ ƐƚĂŶĚƐ
ǁŝƚŚ ĐůĂŵƉƐ͕ ƚƌŝƉŽĚ ƐƚĂŶĚ͕ ĞƚĐ͘