[2 Mark Question Answer]

Question 12 Marks

Copy and complete the following table which refers to the action of heat on some carbonates:

Carbonate	Colour of residue on cooling
Zinc Carbonate
Lead Carbonate
Copper Carbonate

Answer

Carbonate	Colour of residue on cooling
Zinc Carbonate	white
Lead Carbonate	yellow
Copper Carbonate	black

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Question 22 Marks

Explain their cleansing action?

Answer

The cleansing action of both soaps and detergents results from their ability to lower the surface tension of water, to emulsify oil or grease and to hold them in a suspension in water. This ability is due to the structure of soaps and detergents. In water, a sodium soap dissolves to form soap anions and sodium cations.

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Question 32 Marks

Why do they differ in their actions?

Answer

Soaps are sodium or potassium salts of long-chain carboxylic acids. ...Detergents are ammonium or sulphonate salts of long-chain carboxylic acids. Detergents have better cleansing action as compared to soaps. Detergents are made from petrochemicals.

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Question 42 Marks

What are soaps and detergents?

Answer

Soaps and Detergents are chemical compound or mixture of compounds used as a cleansing agent. Soap is a sodium salt or potassium salt of many combinations of fatty acids having cleansing action in water whereas Detergent surfactants are much better solutions for the cleaning purpose as the hardness of water does not affect them.

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Question 52 Marks

How the temporary and permanent hardness is removed?

Answer

Temporary hardness can easily be removed by boiling. permanent hardness can be removed by the following methods:-
(i) By the addition of washing soda
(ii) By ion exchange method
(iii) By the use of polyphosphate water softener

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Question 62 Marks

What do you understand by permanent hardness?

Answer

Permanent hardness refers to the mineral content in the water that is not possible to remove through boiling. The hardness is typically caused by the presence in water of magnesium sulfates and/or calcium sulfate that do not undergo precipitation at increased temperatures.
Therefore, permanent hardness is the sum of magnesium hardness and calcium hardness.

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Question 72 Marks

What do you understand by soft water?

Answer

Soft water is water that has a relatively low concentration of calcium carbonate and other ions. The water that lathers with soap easily is called soft water. It describes the type of water that contains few or no minerals like calcium (Ca) or magnesium (Mg) ions.

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Question 82 Marks

How will you distinguish between temporary hard water and permanent hard water?

Answer

Hard water contains dissolved magnesium and calcium ions. Temporary hardness is caused by dissolved calcium hydrogen carbonate (which is removed by boiling). Permanent hardness is caused by dissolved calcium sulfate (which is not removed by boiling).

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Question 92 Marks

How will you distinguish between soft water and hard water?

Answer

Hard water... is water that contains an appreciable quantity of dissolved minerals (like calcium and magnesium).Soft water is treated water in which the only ion is sodium. As rainwater falls, it is naturally soft. On the other hand, soft water tastes salty and is sometimes not suitable for drinking.

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Question 102 Marks

What do you observe when dilute sulphuric acid is added to Zinc granules.

Answer

When Zn is reacted with dilute sulphuric acid, zinc chloride is formed and hydrogen gas is liberated. This reaction is exothermic and hence heat is evolved in the reaction.

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Question 112 Marks

What do you observe when dilute sulphuric acid is added to the following:
Sodium carbonate

Answer

When dilute sulphuric acid is added to sodium carbonate, the corresponding salt, sodium sulphate, and water are formed and carbon dioxide gas is evolved.
$\mathrm{H}_2 \mathrm{SO}_4+\mathrm{Na}_2 \mathrm{CO}_3 \longrightarrow \mathrm{Na}_2 \mathrm{SO}_4+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2$

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Question 122 Marks

State the original colour of the following substance and colour of residue obtained after heating.
Lead nitrate

Answer

Lead nitrate is a white coloured solid. When lead nitrate is heated, it decomposes to give lead oxide, nitrogen dioxide, and oxygen. ... Hence, the colour of the residue obtained by heating lead nitrate is yellow.

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Question 132 Marks

Write your observation and a balanced equation in the case of the following substances being heated.
Ammonium chloride

Answer

When ammonium chloride is heated White crystalline solid, on strong heating, sublimates to form a basic gas $\left(\mathrm{NH}_3\right)$ and an acidic gas $(\mathrm{HCl})$
$\mathrm{NH}_4 \mathrm{Cl} \underset{\text { Cool }}{\stackrel{\text { Heat }}{\rightleftharpoons}} \mathrm{NH}_3 \uparrow+\mathrm{HCl} \uparrow$

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Question 142 Marks

Write your observation and a balanced equation in the case of the following substances being heated.
Zinc carbonate.

Answer

Zinc carbonate on heating decomposes to zinc oxide and carbon dioxide gas.
$\mathrm{ZnCO}_3(\mathrm{~s}) \longrightarrow \mathrm{ZnO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g}) \uparrow$
This is similar to the decomposition of limestone $(\mathrm{CaCO} 3 \mathrm{CaCO} 3)$ to quick lime $(\mathrm{CaOCaO})$ and carbon dioxide.

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Question 152 Marks

Write your observation and a balanced equation in the case of the following substances being heated.
Copper carbonate.

Answer

Investigating what happens when a compound copper carbonate is heated. When green copper carbonate $\{\mathrm{CuCO} 3\}$ is heated it decomposes forming copper oxide $\{\mathrm{CuO}\}$ and carbon dioxide $\{\mathrm{CO} 2\}$.
$\underset{\text { Green }}{\mathrm{CuCO}_3(\mathrm{~s})} \xrightarrow{\text { Heat }} \underset{\text { Black }}{\mathrm{CuO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})}$

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Question 162 Marks

What do you observe when Cobalt chloride paper is introduced in water vapour.

Answer

It turns blue cobalt chloride paper pink.
$\underset{\text { Blue }}{\mathrm{CoCl}_2}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\text { (Pink) }}{\mathrm{CoCl}_2 \cdot 2 \mathrm{H}_2 \mathrm{O}}$

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Question 172 Marks

What do you observe when $Cl_2$ is passed through potassium iodide (KI) solution.

Answer

If in the solution of $\mathrm{KI}$ (Potassium iodide), we pass Chlorine gas $\left(\mathrm{Cl}_2\right)$, then Chlorine will displace iodine from $\mathrm{KI}$, and form Potassium Chloride ( $\mathrm{KCl})$, and liberates iodine,
$\mathrm{Cl}_2(\mathrm{aq})+2 \mathrm{KI}(\mathrm{aq}) \longrightarrow 2 \mathrm{KCl}(\mathrm{aq})+\mathrm{I}_2(\mathrm{aq})$
When lodine gas is passed into starch solution the solution becomes blue-black in colour.

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Question 182 Marks

What do you observe when $H_2S$ is passed through a lead nitrate solution.

Answer

When gas is passed to lead nitrate solution it also turns black.
$\underset{\text { (colourless) }}{\mathrm{Pb}\left(\mathrm{NO}_3\right)_2}+\mathrm{H}_2 \mathrm{~S} \longrightarrow \underset{\text { (Black) }}{\mathrm{PbS}}+2 \mathrm{HNO}_3$

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Question 192 Marks

What do you observe when HCI is passed through a silver nitrate solution.

Answer

When the gas is passed through a silver nitrate solution, a white precipitate of silver chloride is formed.
$\mathrm{AgNO}_3(\mathrm{aq})+\mathrm{HCI} \longrightarrow \mathrm{AgCI} \downarrow+\mathrm{HNO}_3$
The precipitate dissolves in excess $\mathrm{NH}_4 \mathrm{OH}$.

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Question 202 Marks

What do you observe when $CO_2 $is passed through lime water first and then a little in excess.

Answer

When the gas is passed through lime water, it turns milky due to the formation of a white precipitate of calcium carbonate.
$\mathrm{Ca}(\mathrm{OH})_2+\mathrm{CO}_2 \longrightarrow \mathrm{CaCO}_3 \downarrow+\mathrm{H}_2 \mathrm{O}$
The milkiness disappears when $\mathrm{CO} 2$ is passed in excess.
$\underset{\text { Black }}{\mathrm{CaCO}_3}+\mathrm{CO}_2 \longrightarrow \underset{\text { (Soluble) }}{\mathrm{H}_2 \mathrm{O}}+\underset{\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2}{\mathrm{Ca}}$

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Question 212 Marks

Give a chemical test to distinguish between the following gases.
$NH_3$ and $SO_2$

Answer

	Ammonia ($NH_3$)	Sulphur dioxide ($SO_2$)
Litmus test	Moist red litmus blue.	Moist blue litmus red.

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Question 222 Marks

Give a chemical test to distinguish between the following gases.
$SO_2$ and $Cl_2$

Answer

Sulphur dioxide	Chlorine.
Colour of gas:The gas is colourless.	Colour of gas: The gas is greenish-yellow.

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Question 232 Marks

Give a chemical test to distinguish between the following gases.
$NH_3$ and $HCl$

Answer

Ammonia	Hydrogen chloride
Litmus test: Moist red litmus blue.	Litmus test: Moist blue litmus paper red.

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Question 242 Marks

Give a chemical test to distinguish between the following gases
HCl and $Cl_2$

Answer

Hydrogen chloride	Chlorine
Colour of gas: The gas is colourless.	Colour of gas: The gas is greenish-yellow.

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Question 252 Marks

Give a chemical test to distinguish between the following gases.
HCl and $H_2S$

Answer

Hydrogen chloride	Hydrogen sulphide
Odour of gas: Pungent choking odour.	Odour of gas: Smell as of rotten eggs.

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Question 262 Marks

Give a chemical test to distinguish between the following gases.
$CO_2$ and $SO_2$

Answer

Carbon dioxide	sulphur dioxide
Litmus test: It turns moist blue litmus faint red.	Litmus test: It turns moist blue litmus red and finally bleaches it. This bleaching is temporary.
The gas has no effect on filter paper dipped in acidified $K_2Cr_2O_7$ or $KMnO_4.$	It has no effect on lead acetate paper (Distinct from $H_2S$). This test distinguishes it from $H_2S.$

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Question 272 Marks

Give a chemical test to distinguish between the following gases.
$H_2$ and $O_2$

Answer

Hydrogen	Oxygen
Apply a burning splint to the gas: Pure hydrogen burns with a pale blue Flame when a burning splint is brought near it.	Apply a burning splint to the gas: It rekindles a glowing wooden splinter.

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Question 282 Marks

Give a chemical test to distinguish between the following gases.
$H_2$ and $CO_2$

Answer

Hydrogen	Carbon dioxide
Litmus test: Neutral	Litmus test: Moist blue litmus faint red

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