Page 68 - Chemistry ICSE Class X

Study of
3 Acids, Bases and Salts

Elements combine with each other to give compounds. About three million
CONTENTS NCMJ EQORQWPFU CTG MPQYP 6JGUG EQORQWPFU OC[ DG ENCUUKſGF QP
the basis of their properties, such as colour, taste, solubility and chemical
ͻ Acids DGJCXKQWT 6JG GCTNKGUV ENCUUKſECVKQP QH EQORQWPFU KPVQ acids, bases and
ͻ ůĂƐƐŝĮĐĂƟŽŶ ŽĨ ĂĐŝĚƐ salts was primarily based on their taste and action on litmus.
ͻ 'ĞŶĞƌĂů ŵĞƚŚŽĚƐ ŽĨ ƉƌĞƉĂƌĂƟŽŶ ŽĨ
acids Acids have sour taste and are corrosive. Bases have bitter taste and
ͻ 'ĞŶĞƌĂů ƉƌŽƉĞƌƟĞƐ ŽĨ ĂĐŝĚƐ soapy touch. Most acids and bases are available both in the solid as well as
liquid (or solution) forms. Salts are solids and may be tasteless, colourless
ͻ hƐĞƐ ŽĨ ĂĐŝĚƐ
or may have characteristic taste and colour.
ͻ Bases
ͻ ůĂƐƐŝĮĐĂƟŽŶ ŽĨ ďĂƐĞƐ
Acids
ͻ 'ĞŶĞƌĂů ŵĞƚŚŽĚƐ ŽĨ ƉƌĞƉĂƌĂƟŽŶ ŽĨ
ďĂƐĞƐ
ͻ 'ĞŶĞƌĂů ƉƌŽƉĞƌƟĞƐ ŽĨ ďĂƐĞƐ The word acid is derived from the Latin word acidus which means sour.
ͻ hƐĞƐ ŽĨ ďĂƐĞƐ
What are the acids
ͻ /ŽŶƐ ƉƌĞƐĞŶƚ ŝŶ ĂĐŝĚƐ͕ ďĂƐĞƐ͕ ĂůŬĂůŝƐ
ĂŶĚ ƚŚĞŝƌ ƐŽůƵƟŽŶƐ The compounds whose molecule contains one or more hydrogen atoms
ͻ dŚĞ Ɖ, ƐĐĂůĞ that can be replaced by active metals is called an acid. The displaced
ͻ dĞƐƟŶŐ ƚŚĞ ĂĐŝĚŝƚLJ͕ ŶĞƵƚƌĂůŝƚLJ ĂŶĚ hydrogen is given off as a gas.
ĂůŬĂůŝŶŝƚLJ ŽĨ Ă ƐŽůƵƟŽŶ ƵƐŝŶŐ Ɖ, Zinc (Zn) displaces hydrogen from a compound H SO .
ƉĂƉĞƌ ĂŶĚ ƵŶŝǀĞƌƐĂů ŝŶĚŝĐĂƚŽƌ H SO (aq) + Zn(s) o ZnSO (aq) 2 + 4 H (g)
ͻ ^ĂůƚƐ 2 4 4 2
ͻ ůĂƐƐŝĮĐĂƟŽŶ ŽĨ ƐĂůƚƐ hydrogen gas
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ͻ 'ĞŶĞƌĂů ƉƌŽƉĞƌƟĞƐ ŽĨ ƐĂůƚƐ Thus, H SO is an acid.
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ͻ ĞĐŽŵƉŽƐŝƟŽŶ ŽĨ According to Arrhenius, an acid is a hydrogen containing compound
ŚLJĚƌŽŐĞŶĐĂƌďŽŶĂƚĞƐ ;ďŝĐĂƌďŽŶĂƚĞƐͿ͕ which gives free hydrogen ions when dissolved in water.
ĐĂƌďŽŶĂƚĞƐ͕ ĐŚůŽƌŝĚĞƐ ĂŶĚ ŶŝƚƌĂƚĞƐ For example, hydrochloric acid (HCl), sulphuric acid (H SO ), nitric
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2
ďLJ ĂĐŝĚƐ acid (HNO ), phosphoric acid (H PO ), acetic acid (CH COOH) are some
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3
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ͻ 'ĞŶĞƌĂů ŵĞƚŚŽĚƐ ŽĨ ƉƌĞƉĂƌĂƟŽŶ ŽĨ commonly used acids. All these compounds when dissolved in water give
ƐŽůƵďůĞ ƐĂůƚƐ free hydronium ion (H O ) in the solution.
+
ͻ 'ĞŶĞƌĂů ŵĞƚŚŽĚƐ ŽĨ ƉƌĞƉĂƌĂƟŽŶ ŽĨ 3
–
ŝŶƐŽůƵďůĞ ƐĂůƚƐ HCl(aq) + H O o H O (aq) + Cl (aq)
+
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3
ͻ >ĂďŽƌĂƚŽƌLJ ƉƌĞƉĂƌĂƟŽŶ ŽĨ ƐŽŵĞ hydrochloric acid water (excess) hydronium ion chloride ion
ŶŽƌŵĂů ĂŶĚ ĂĐŝĚ ƐĂůƚƐ
2–
+
ͻ ,LJĚƌĂƚĞĚ ƐĂůƚƐ ĂŶĚ ǁĂƚĞƌ ŽĨ H SO (aq) + 2H O o 2H O (aq) + SO (aq)
2
2
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ĐƌLJƐƚĂůůŝƐĂƟŽŶ sulphuric acid water (excess) hydronium ion sulphate ion
ͻ ŋŽƌĞƐĐĞŶĐĞ CH COOH + H O o H O (aq) + CH COO (aq)
+
–
ͻ ,LJŐƌŽƐĐŽƉŝĐ ƐƵďƐƚĂŶĐĞƐ 3 2 3 3
acetic acid water (excess) hydronium ion acetate ion
ͻ ĞůŝƋƵĞƐĐĞŶƚ ƐƵďƐƚĂŶĐĞƐ
What are the characteristics of acids
Acids are characterised by the following characteristics:
ƒ Acids have sour taste.
ƒ Acids turn blue litmus to red.
ƒ Acids react with active metals, such as zinc, magnesium and iron, to
produce hydrogen gas.
ƒ Acids when dissolved in water provide conducting solutions.