[3 Mark Question Answer]

Question 13 Marks

Name the salt used in :
$a.$ The manufacture of glass and soap.
$b.$ The manufacture of fertilizers
$c.$ Fire extinguishers

Answer

$(a)$ Washing soda $($hydrated sodium carbonate$) – Na_2CO_3.10H_2O$
$(b)$ Nitre $($potassium nitrate$) – KNO_{3}$
$(c)$ Baking soda $($sodium hydrogencarbonate$) – NaHCO_3$

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Question 23 Marks

Name :
$a.$ Two bases which are not alkalis
$b.$ A normal salt and an acid salt of the same acid

Answer

$(a)$ Copper hydroxide $[Cu(OH)_2],$ iron hydroxide $[Fe(OH)_2]$
$(b)$ Normal salt of carbonic acid $-$ sodium carbonate $(Na_2CO_3),$
Acid salt of carbonic acid $-$ sodium hydrogencarbonate $(NaHCO_3)$

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Question 33 Marks

State two uses for each of the following acids :
a. Hydrochloric acid
b. Nitric acid
c. Sulphuric acid

Answer

(a) Uses of hydrochloric acid – It is used

in the preparation of aqua regia, which dissolves noble metals.
in the stomach to provide an acidic medium for the digestion of food.

(b) Uses of nitric acid – It is used

in the manufacture of fertilizers such as ammonium nitrate.
in the manufacture of explosives such as TNT (trinitrotoluene) and nitroglycerine.

in the refining of petroleum
in lead-acid storage batteries and Tire extinguishers.

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Question 43 Marks

What is the difference between a strong acid and a weak acid ? Give two examples of each of them.

Answer

Acids that undergo complete dissociation in aqueous solution producing a high concentration of hydrogen ions $($or hydronium ions$)$ are called strong acids.
Examples : nitric acid $(HNO_3),$ sulphuric acid $(H_2SO_4),$ hydrochloric acid $(HCl),$ etc.
Acids that undergo partial dissociation in aqueous solution producing a low concentration of hydrogen ions $($or hydronium ions$)$ are called weak acids.
Examples : carbonic acid $(H_2CO_3),$ phosphoric acid $(H_3PO_4),$ formic acid, acetic acid, etc.

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Question 53 Marks

While diluting a concentrated acid why is it recommended that the acid should be added to water and not water to the acid ?

Answer

Diluting a concentrated acid :
The process of dissolving an acid in water is a highly exothermic reaction. Care must be taken while mixing concentrated acids (specifically, strong acids) with water. Always add acid to water and not the other way round. The acid must always be added slowly to water with constant stirring.
But, if water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause bums. The glass container may also break due to excessive heating.

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Question 63 Marks

What is the difference between a strong base and a weak base ? Explain with examples.

Answer

Bases that undergo complete dissociation in aqueous solution and produce a high concentration of hydroxide ions $(OH^–)$ in solution are called strong bases.
Examples : Potassium hydroxide $(KOH)$ and sodium hydroxide $(NaOH)$. Bases that undergo partial dissociation in aqueous solution and produce a low concentration of hydroxyl ions $(OH^–)$ in solution are called weak bases.
Examples : Magnesium hydroxide $[Mg(OH)_2]$ and ammonium hydroxide $[NH_4OH]$.

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Question 73 Marks

What are indicators ? Name the three common acid- base indicators and give their colours in acidic and basic solutions.

Answer

An indicator is a chemical substance that is used to identify whether a given substance is an acid or a base by a sharp change in its colour. The three most common acid-base indicators are litmus, methyl orange and phenolphthalein

Indicator	Color change
	Neutral	Acidic	Basic
Litmus	Purple	Red	Blue
Methyl	Orange	Red	Yellow
Phenolphthalein	Colorless	Colorless	Pink

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