Page 76 - Chemistry ICSE Class X

64 ICSE Chemistry – 10

ϯ͘ ,Žǁ ǁŝůů LJŽƵ ŽďƚĂŝŶ ŚLJĚƌŽĐŚůŽƌŝĐ ĂĐŝĚ ĨƌŽŵ ƐŽĚŝƵŵ ĐŚůŽƌŝĚĞ͍ tƌŝƚĞ ƚŚĞ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ͘
ϰ͘ EĂŵĞ ƚŚĞ ƚǁŽ ŽdžŝĚĞƐ ǁŚŝĐŚ ǁŚĞŶ ĚŝƐƐŽůǀĞĚ ŝŶ ǁĂƚĞƌ ŐŝǀĞ ĐŽƌƌĞƐƉŽŶĚŝŶŐ ĂĐŝĚƐ͘
ϱ͘ tƌŝƚĞ ƚŚĞ ďĂůĂŶĐĞĚ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶ ĨŽƌ ƚŚĞ ĨŽůůŽǁŝŶŐ ƌĞĂĐƟŽŶƐ͘
;ĂͿ ĐƟǀĞ ŵĞƚĂů н ĐŝĚ o ^Ăůƚ н ,LJĚƌŽŐĞŶ
;ďͿ ĐŝĚ н ĂƌďŽŶĂƚĞ o ^Ăůƚ н tĂƚĞƌ н ĂƌďŽŶ ĚŝŽdžŝĚĞ
;ĐͿ ĐŝĚ н DĞƚĂů ŽdžŝĚĞ o ^Ăůƚ н tĂƚĞƌ
;ĚͿ DĞƚĂů ƐƵůƉŚŝĚĞ н ĐŝĚ o DĞƚĂů ƐĂůƚ н ,LJĚƌŽŐĞŶ ƐƵůƉŚŝĚĞ
ϲ͘ EĂŵĞ ĂŶ ĂĐŝĚ ƵƐĞĚ
;ĂͿ ƚŽ ŇĂǀŽƵƌ ĂŶĚ ƉƌĞƐĞƌǀĞ ĨŽŽĚ
;ďͿ ŝŶ Ă ĚƌŝŶŬ
;ĐͿ ĨŽƌ ƉƌĞƉĂƌŝŶŐ ĂŶ ĞLJĞ ǁĂƐŚ
;ĚͿ ŝŶ ďĂƩĞƌŝĞƐ
;ĞͿ ĨŽƌ ĐůĞĂŶŝŶŐ ŝƌŽŶ ƐŚĞĞƚƐ ďĞĨŽƌĞ ŐĂůǀĂŶŝnjĂƟŽŶ͘

Bases

What are the bases
+
The oxides and hydroxides of metals or metal-like radicals (such as NH ,
4
ammonium ion) are called bases.
or
+
A base is a compound which accepts a proton (H ) given by an acid.
or
+
A base is a compound which combines with the H ion of an acid to
form a salt and water only.
The bases which are highly soluble in water and contain one or more
–
hydroxyl ion (OH ) in their molecules are called alkalis.
It should be noted that while all alkalis are bases, all bases are not
alkalis. For example,
ƒ Both sodium hydroxide (NaOH) and copper hydroxide [Cu(OH) ]
2
are bases.
ƒ Sodium hydroxide (NaOH) is highly soluble in water. So sodium
hydroxide (NaOH) is an alkali.
ƒ Copper hydroxide [Cu(OH) ] is insoluble in water. So, copper
2
hydroxide is not an alkali, (it is a base).
What are the characteristics of bases
Bases show the following characteristics:
ƒ Bases have bitter taste.
ƒ Bases have a soapy touch.
ƒ Bases turn red litmus blue.
ƒ Some bases dissolve in water forming a conducting solution.
ƒ Soluble bases (or alkalis) react with metals, such as zinc, aluminium
and lead, to evolve hydrogen gas.

Classification of Bases

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ƒ On the basis of strength
ƒ On the basis of acidity