[5 Mark Question Answer]

Question 14 Marks

What is the difference between an acid salt and a normal salt ?

Answer

A salt formed by the complete replacement of the hydrogen ions of an acid molecule (monobasic) by a metal ion or a positive ion is called a normal salt.
Example :
$\underset{\text {carbonic acid}}{H_2CO_3} + \underset{\text {sodium hydroxide}}{2NaOH} \longrightarrow \underset{\text {sodium carbonate}}{Na_2CO_3} + \underset{\text {water}}{2H_2O}$
A salt formed by the partial replacement of the hydrogen ions of an acid molecule (dibasic or tribasic) by a metal ion or a positive ion is called an acid salt.
Example:
$\underset{\text {carbonic acid}}{H_2CO_3} + \underset{\text {sodium hydroxide}}{NaOH} \longrightarrow \underset{\text {sodium hydrogen carbonate}}{NaHCO_3} + \underset{\text {water}}{2H_2O}$

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Question 24 Marks

State one important use of the following :
$a.$ Caustic soda
$b.$ Slaked lime
$c.$ Ammonium hydroxide
$d.$ Magnesium hydroxide

Answer

$(a)$ Uses of caustic soda $($sodium hydroxide$, NaOH)$ : Used in the manufacture of soap, paper, medicines, artificial silk $($rayon$)$ and in the refining of petroleum.
$(b)$ Uses of slaked lime $[$calcium hydroxide$, Ca(OH)_2]$: Used to make cement, mortar, bleaching powder and neutralizing acidic soil.
$(c)$ Uses of ammonium hydroxide $(NH_4OH)$ : Used to remove grease stains from glass panes and in the manufacture of nylon, plastic, fertilizers, dyes, etc.
$(d)$ Uses of magnesium hydroxide $[$milk of magnesia$, Mg(OH_2)]$ : Used as an antacid to neutralize the acidity caused by the excess secretion of hydrochloric acid in the stomach.

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Question 34 Marks

What happenswhen an acid reacts with a base ? Explain by giving a suitable example. What is the special name for such a reaction ?

Answer

When an acid reacts with a base, it forms salt and water. This reaction is called a neutralization reaction.
acid + base → salt + water
The base neutralizes the acid and the salt formed is neutral in nature, and therefore, the reaction is called neutralization reaction.
For example, when hydrochloric acid reacts with sodium hydroxide solution a neutralization reaction takes place to form sodium chloride and water.
$\underset{\text {sodium hydroxide (base)}}{NaOH} + \underset{\text {hydrochloric acid (acid)}}{HCl} \longrightarrow \underset{\text {sodium chloride (salt)}}{NaCl} + \underset {\text {water}}{H_2O}$

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Question 44 Marks

Define the basicity of an acid. Also differentiate between monobasic, dibasic and tribasic acids.

Answer

The basicity of an acid is the number of hydrogen ions $(H^+)$ produced by the dissociation of one molecule of the acid when dissolved in water. Depending upon the number of hydrogen ions produced per molecule$,$ acids are classified as monobasic$,-$ dibasic and tribasic.
Monobasic acid $-$ Acids which dissociate on dissolving in water to produce one hydrogen ion $(H^+)$ per molecule of the acid are called monobasic acids.
$\underset{\text {hydrochloric acid}}{HCl} \longrightarrow \underset{\text {1 hydrogen ion}}{H^+} + \underset{\text {1 chloride ion}}{Cl^-}$
Basicity $= 1$ as the number of $H^+ = 1$
Examples : hydrochloric acid $(HCl),$ nitric acid $(HNO_3),$ and
acetic acid $(CH_3),COOH.$
Dibasic acid $-$ Acids which dissociate on dissolving in water to produce two hydrogen ions $(H^+)$ per molecule of the acid are called dibasic acids. img
Basicity $= 2$ as the number of $H^+ = 2$
Examples : sulphuric acid $(H_2SO_4),$ carbonic acid $(H_2CO_3),$ oxalic acid$,$ etc.
Tribasic acid $-$ Acids which dissociate in water to produce three hydrogen ions $(H^+)$ per molecule of the acid are called
tribasic acids.
$\underset{\text {sulphuric acid}}{H_2SO_4} \longrightarrow \underset{\text {2 hydrogen ions}}{2H^+} + \underset{\text {1 sulphate ion}}{SO_4^2-}$
Basicity $= 3$ as the number of $H^+ = 3$
Examples : Phosphoric acid $(H_3PO_4)$ and phosphorous acid $(H_3PO_3)$

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