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Chemistry [2 Mark Question Answer]

Acids,Bases and Salts · ICSE STD 10 (ICSE - English Medium). 10 questions.

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[2 Mark Question Answer]

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Question 12 Marks
Mention the terms defined by the following sentences :
(i) A soluble base
(ii) An insoluble solid formed, when two solutions are mixed together.
Answer
(i) A soluble base is an alkali.
(ii) An insoluble solid formed when two solutions are mixed together is precipitate.
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Question 22 Marks
Give one chemical property (not indicators) with a balanced equation in each case which are typical of (i) a dilute acid (ii) a dilute aqueous alkali.
Answer
(i) Dilute acid reacts with active metals to form a metallic salt and hydrogen gas.
Zn + H2SO4(dil.) → ZnSO4 + H2(g)
(ii) Dilute alkali reacts with an acid to form salt and water as the only products.
NaOH + HCl → NaCl + H2O
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Question 32 Marks
1 molar solution of acetic acid is a weak acid as compared to 0.1 molar solution of hydrochloric acid. Why? Explain your answer.
Answer
1 molar solution of acetic has a degree of dissociation less that 4%, whereas 0.1 molar solution of hydrochloric acid has degree of dissociation more than 90%.
Now, as the degree of dissociation determines the strength, therefore, 0.1 molar hydrochloric acid is a strong acid, but 1 molar acetic acid is a weak acid.
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Question 42 Marks
Write fully balanced chemical equations for the reaction of conc. sulphuric acid with (i) metallic chloride (ii) metallic nitrate. Explain, why the chlorides and nitrates form their respective acids.
Answer
(i) $2 NaCl + H _2 SO _4$ (conc.) $\xrightarrow{\text { heat }} Na _2 SO _4+2 HCl$
(ii) $2 KNO _3+ H _2 SO _4$ (conc.) $\xrightarrow{\text { heat }} K _2 SO _4+2 HNO _3$
It is because, a less volatile acid always displaces more volatile acid from its salt.
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Question 52 Marks
How will you obtain (i) sulphuric acid from an acidic oxide, and (ii) potassium hydroxide from a basic oxide?
Answer
(i) When sulphur trioxide (acidic oxide) is dissolved in water, an exothermic reaction takes place with the formation of sulphuric acid.
$SO _3+ H _2 O \longrightarrow H _2 SO _4$
(ii) When potassium oxide (basic oxide) is dissolved in water, an exothermic reaction takes place with the for- mation of potassium hydroxide
$K _2 O + H _2 O \longrightarrow 2 KOH$
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Question 62 Marks
Explain why is the basicity of acetic acid is one, and the acidity of magnesium hydroxide is 2.
Answer
Acetic acid dissociates to produce one H+(aq) ion per molecule and hence its basicity is one.
$CH _3 COOH + H _2 O \rightleftharpoons H _3 O ^{+}+ CH _3 COO ^{-}$
Magnesium hydroxide reacts completely with 2H+(aq) ions of an acid to form salt and water, therefore its acidity is 2.
Mg(OH)2 + H2SO4 → MgSO4 + 2H2O
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Question 72 Marks
Differentiate between a strong alkali and a weak alkali.
Answer
An alkali, which almost dissociates completely in an aqueous solution, thereby producing high concentration of OH- ions is called a strong alkali. For example, lithium hydroxide, sodium hydroxide and potassium hydroxide. An alkali, which dissociates partially in an aqueous solution, thereby producing a low concentration of OH- ions is called a weak alkali. For example, ammonium hydroxide, calcium hydroxide and magnesium hydroxide.
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Question 82 Marks
Differentiate between a strong acid and weak acid. Give two examples.
Answer
An acid which dissociates almost completely in an aqueous solution, thereby producing high concentration of H+ (aq) ions is called a strong acid. For example, hydrochloric acid, nitric acid, sulphuric acid and phosphoric acid.
An acid which dissociates only partially in an aqueous solution thereby producing low concentration of H+(aq) ions is called a weak acid.
For example, acetic acid, carbonic acid, sulphurous acid, nitrous acid are weak acids.
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Question 92 Marks
On what basis are the strength of (i) acids, (ii) alkalis determined?
Answer
(i) The strength of an acid is determined by the concentration of hydronium ions present in its aqueous solution.
(ii) The strength of an alkali is determined by the concentration of hydoxyl ions present in its solution.
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Question 102 Marks
Differentiate between hydracids and oxy-acids. Give examples.
Answer
Hydracids : Mineral acids containing hydrogen and one non-metallic element, other than oxygen are called hydracids. For example HCl, HBr, H2S, etc.
Oxy-acids : Mineral acids containing hydrogen, one non-metallic element and oxygen are called oxyacids. For example H2SO4, HNO3, H2SO3, H2CO3 etc.
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