[2 Mark Question Answer] - Chemistry STD 10 Questions - Vidyadip

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[2 Mark Question Answer]

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Question 12 Marks

From the list of the following salts choose the salt that most appropriately fits the description given in the following :
$\left[ AgCl , MgCl _2, NaHSO _4, PbCO _3, ZnCO _3, KNO _3, Ca \left( NO _3\right)_2\right]$
(i) A deliquescent salt
(ii) An insoluble chloride
(iii) On heating this salt gives a yellow residue when hot and white when cold
(iv) On heating this salt, a brown coloured to prepare the following salts:

Answer

(i) A deliquescent salt: $MgCl _2$
(ii) An insoluble chloride : AgCl
(iii) On heating, this salt gives a yellow residue when hot and a white residue when cold: $ZnCO _3$
(iv) On heating this salt, a brown-coloured gas is evolved: $Ca \left( NO _3\right)_2$

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Question 22 Marks

State your observation of the following case :
When calcium hydroxide is heated with ammonium chloride crystals.

Answer

When ammonium chloride is heated with calcium hydroxide, ammonia gas is released.
$2 NH _4 Cl + Ca ( OH )_2 \rightarrow CaCl _2+2 NH _3+2 H _2 O$
The liberated gas turns red litmus blue.

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Question 32 Marks

State your observation of the following case :
When excess sodium hydroxide is added to calcium nitrate solution.

Answer

Calcium nitrate solution on reaction with excess of sodium hydroxide produces calcium hydroxide and sodium nitrate. Calcium nitrate reacts with excess of sodium hydroxide to form a white precipitate of calcium hydroxide, which is sparingly soluble, and colourless sodium nitrate.
The reaction is as follows:
$Ca \left( NO _3\right)_2+2 NaOH \rightarrow Ca ( OH )_2+2 NaNO _3$

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Question 42 Marks

State your observation of the following case :
When dilute hydrochloric acid is added to sodium carbonate crystals.

Answer

Sodium carbonate crystals on reaction with dilute HCl form sodium chloride, water and carbon dioxide, which is evolved with brisk effervescence. This is a neutralisation reaction as sodium carbonate is a basic salt, while hydrochloric acid is an acid.
The chemical equation for this reaction is as follows:
$Na _2 CO _3+2 HCl \rightarrow 2 NaCl + H _2 O + CO _2$

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Question 52 Marks

Distinguish between the following pairs of compounds using the test given with brackets :
Dilute sulphuric acid and dilute hydrochloric acid (using barium chloride solution)

Answer

Sulphuric acid precipitates the insoluble sulphate of barium from the solution of barium chloride.
$BaCl _2+ H _2 SO _4 \rightarrow BaSO _4+2 HCl$
Dilute HCl does not react with barium chloride solution, and thus, no precipitate is produced in the reaction.

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Question 62 Marks

Give one test to distinguish between the following pair of chemicals.
Iron (III) Chloride solution and copper chloride solution.

Answer

Iron (III) chloride solution and copper chloride solution can be distinguished by using ammonium hydroxide. Copper forms a blue ppt. of $Cu ( OH ) 2$ which is soluble in excess of ammonium hydroxide.
$
CuCl _2+2 NH _4 OH \longrightarrow Cu ( OH )_2+2 NH _4 Cl
$
Whereas iron(III) forms a reddish brown ppt. of $Fe ( OH )_3$ which is insoluble even in excess of ammonium hydroxide.
$
FeCl _3+3 NH _4 OH \longrightarrow Fe ( OH )_3+3 NH _4 Cl
$

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Question 72 Marks

Give one test to distinguish between the following pair of chemicals.
Sodium nitrate solution and sodium chloride solution.

Answer

Sodium chloride solution and sodium nitrate solution can be distinguished by using conc. Sulphuric acid to the salt solution, add freshly prepared ferrous sulphate solution and pour a few drops of conc. H2SO4 along the sides of the tube. If its sodium nitrate solution then a brown ring would appear at the junction of the two liquid layers. But if its sodium chloride solution, it would not undergo any visible reaction.

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Question 82 Marks

Give one test to distinguish between the following pair of chemical.
Zinc nitrate solution and calcium nitrate solution.

Answer

Zinc nitrate and calcium nitrate solution can be distinguished by reaction with ammonium hydroxide. Zinc forms a white gelatinous ppt. whereas there is no precipitation of calcium hydroxide even with excess of ammonium hydroxide.
$
Zn \left( NO _3\right)_2+2 NH _4 OH \longrightarrow \underset{\text { White gelatinous ppt. }}{ Zn ( OH )_2 \downarrow}+2 NH _4 NO _3
$

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Question 92 Marks

The questions (i) to (v) refer to the following salt solutions listed (a) to (f):
(a) Copper nitrate
(b) Iron (II) sulphate
(c) Iron (III) chloride
(d) Lead nitrate
(e) Magnesium sulphate
(f) Zinc chloride
(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride solution ?
(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution ?
(iii) Which solution will give a white precipitate when either dilute hydrochloric acid or dilute sulphuric acid is added to it?
(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it ?
(v) Which solution gives a white precipitate with excess ammonium hydroxide solution?

Answer

(i) Magnesium sulphate, Iron (II) Sulphate
(ii) Zinc chloride, Iron (III) chloride
(iii) Lead nitrate
(iv) Copper nitrate

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Question 102 Marks

Write the observation for the following:
Excess $NH_4OH$ is added to a substance obtained by adding hydrochloric acid in silver nitrate solution.

Answer

Silver chloride is formed on adding hydrochloric acid in silver nitrate solution. On adding excess of ammonium chloride, white ppt. gets dissolved.
$2 AgCl ( s )+2 NH _4 OH (a q) \longrightarrow Ag _2 O (s)+ H _2 O ( I )+2 NH _4 Cl (a q)$

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Question 112 Marks

Write the observation for the following :
$NH_4OH$ is added first in a small quantity and then in excess to a solution of copper sulphate.

Answer

Dropwise addition of $NH _4 OH$ :
$CuSO _4+2 NH _4 OH \longrightarrow \underset{\text { Blue ppt. }}{ Cu ( OH )_2}+\left( NH _4\right)_2 SO _4$
with excess of $NH _4 OH$, the precipitate of copper(II) hydroxide dissolves as:
$Cu ( OH )_2+\left( NH _4\right)_2 SO _4+\underset{\text { In excess }}{2 NH _4 OH } \longrightarrow \underset{\text { Tetrammine copper(II) sulphate }}{\left[ Cu \left( NH _3\right)_4\right] SO _4+4 H _2 O }$

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Question 122 Marks

Write the observation for the following:
NaOH is added drop-wise till in excess to a solution of zinc sulphate.

Answer

When $NaOH$ is added drop-wise to a solution of zinc sulphate, then the following reaction takes place:
$
ZnSO _4+2 NaOH \longrightarrow \underset{\text { White gelatinous ppt. }}{ Zn ( OH )_2 \downarrow}+ Na _2 SO _4
$
When $NaOH$ becomes in excess, then the following reaction takes place:
$
Zn ( OH )_2+2 NaOH \longrightarrow \underset{\text { Colourless }}{ Na _2 ZnO _2}+2 H _2 O
$

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Question 132 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	Red
Copper carbonate	Black

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Question 142 Marks

How would you distinguish between $Zn ^{2+}$ and $Pb ^{2+}$ using ammonium hydroxide solution?

Answer

Distinguish between zinc ion and lead ion.
$
ZnSO _4+2 NH _4 OH \longrightarrow Zn ( OH )_2 \downarrow+\left( NH _4\right)_2 SO _4
$
$Zn ( OH )_2$ forms white gelatinous precipitate. In the presence of excess of ammonium hydroxide these precipitates get dissolved.
$
Pb \left( NO _3\right)_2+2 NH _4 OH \longrightarrow Pb ( OH )_2 \downarrow+2 NH _4 NO _3
$
$Pb ( OH ) 2$ forms white precipitate. This precipitate is insoluble in the presence of excess of ammonium hydroxide.

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Question 152 Marks

State the effect of adding a small amount of : (a) sodium hydroxide (b) ammonium hydroxide followed by an excess in case to samples of the salt solutions.
Lead nitrate [ small amount ________ in excess ________ ]

Answer

Lead nitrate:
a. with sodium hydroxide :
- $Pb ( NO )_3+2 NaOH \longrightarrow Pb ( OH )_2+2 NaNO _3$
- White curdy ppt. is soluble in excess of $NaOH$.
b. With ammonium hydroxide :
- $Pb ( NO )_3+2 NH _4 OH \longrightarrow Pb ( OH )_2+2 NH _4 NO _3$
- White curdy ppt. is insoluble in excess of ammonium hydroxide.

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Question 162 Marks

State the effect of adding a small amount of : (a) sodium hydroxide (b) ammonium hydroxide followed by an excess in case to samples of the salt solutions.
Zinc nitrate [ small amount ________ in excess ________]

Answer

Zinc nitrate:
a. with sodium hydroxide :
- $Zn \left( NO _3\right)+2 NaOH \longrightarrow Zn ( OH )_2+2 NaNO _3$
- On addition of excess of $NaOH$, white ppt. of $Zn ( OH )_2$ dissolves.
b. With ammonium hydroxide :
- $Zn \left( NO _3\right)+2 NH _4 OH \longrightarrow Zn ( OH )_2+2 NH _4 NO _3$
- The gelatinous white insoluble ppt. of $Zn ( OH )_2$ dissolves in excess of ammonium hydroxide.

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Question 172 Marks

State the effect of adding a small amount of : (a) sodium hydroxide (b) ammonium hydroxide followed by an excess in case to samples of the salt solutions.
Calcium nitrate [ small amount __________ in excess __________ ]

Answer

Calcium nitrate:
a. with sodium hydroxide :
- $Ca \left( NO _3\right)_2 \xrightarrow{ NaOH } Ca ( OH )_2+ NaNO _3$
- White curdy ppt. is insoluble in excess of $NaOH$.
b. With ammonium hydroxide :
- $Ca \left( NO _3\right)_2 \xrightarrow{ NH _4 OH } Ca ( OH )_2+ NH _4 NO _3$
- No precipitation of $Ca ( OH )_2$ even in excess of ammonium hydroxide.

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Question 182 Marks

One chemical test that would enable you to distinguish between the following pair of chemicals. Describe what happens with each chemical or state no visible reaction.
Calcium nitrate solution and zinc nitrate solution.

Answer

Calcium nitrate solution and zinc nitrate solution can be distinguished by sodium hydroxide. Sodium hydroxide reacts with zinc nitrate and zinc hydroxide is formed which is soluble in excess of sodium hydroxide.
$
Zn \left( NO _3\right)_2( aq )+2 NaOH ( aq ) \longrightarrow Zn ( OH )_2( s )+2 NaNO _3( aq )
$
Sodium hydroxide reacts with calcium nitrate and forms white ppt. of calcium hydroxide insoluble in excess of sodium hydroxide.
$
Ca \left( NO _3\right)_2+2 NaOH \longrightarrow Ca ( OH )_2+2 NaNO _3
$

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Question 192 Marks

One chemical test that would enable you to distinguish between the following pair of chemicals. Describe what happens with each chemical or state no visible reaction.
Sodium sulphate solution and sodium chloride solution.

Answer

Sodium sulphate solution and sodium chloride solution can be distinguished by using barium chloride solution. Barium chloride solution on being added to sodium sulphate solution forms a white precipitate which is insoluble in conc. HCl whereas sodium chloride shows no reaction with barium chloride solution.

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Question 202 Marks

One chemical test that would enable you to distinguish between the following pair of chemicals. Describe what happens with each chemical or stateno visible reaction.
Sodium chloride solution and sodium nitrate solution.

Answer

Sodium chloride solution and sodium nitrate solution can be distinguished by using conc. sulphuric acid. To the salt solution, add freshly prepared ferrous sulphate solution and pour a few drops of conc. $H_2SO_4$ along the sides of the tube. If its sodium nitrate solution then a brown ring would appear at the junction of the two liquid layers. But if its sodium chloride solution, it would not undergo any visible reaction.

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Question 212 Marks

One chemical test that would enable you to distinguish between the following pair of chemicals. Describe what happens with each chemical or state no visible reaction.
Sodium chloride solution and sodium nitrate solution.

Answer

Sodium chloride solution and sodium nitrate solution can be distinguished by using conc. sulphuric acid. To the salt solution, add freshly prepared ferrous sulphate solution and pour a few drops of conc. $H_2SO_4$ along the sides of the tube. If its sodium nitrate solution then a brown ring would appear at the junction of the two liquid layers. But if its sodium chloride solution, it would not undergo any visible reaction.

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Question 222 Marks

Using Sodium hydroxide solution, how would you distinguish: Iron(II) chloride from Iron (III) chloride

Answer

Iron (III) chloride on reacting with sodium hydroxide forms brown ppt.
$
FeCl _3( aq )+3 NaOH ( aq ) \longrightarrow \underset{\text { brown }}{ Fe ( OH )_3( s )}+3 NaCl ( aq )
$
Iron (II) chloride on reacting with sodium hydroxide forms green ppt.
$
FeCl _2( aq )+2 NaOH ( aq ) \longrightarrow \underset{\text { green }}{ Fe ( OH )_2( s )}+2 NaCl ( aq )
$

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Question 232 Marks

Using Sodium hydroxide solution, how would you distinguish: Zinc nitrate solution from calcium nitrate solution.

Answer

Sodium hydroxide reacts with zinc nitrate and zinc hydroxide is formed which is soluble in excess of sodium hydroxide
$
Zn \left( NO _3\right)_2( aq )+2 NaOH ( aq ) \longrightarrow Zn ( OH )_2( s )+2 NaNO _3( aq )
$
Sodium hydroxide reacts with calcium nitrate and forms white ppt. of calcium hydroxide which is insoluble in excess of sodium hydroxide.
$
Ca \left( NO _3\right)_2+2 NaOH \longrightarrow Ca ( OH )_2+2 NaNO _3
$

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Question 242 Marks

A white solid A when heated with sodium hydroxide solution, gives a pungent gas B, which turns red litmus blue. The solid, when dissolved in dilute nitric acid and treated with silver nitrate gives a white precipitate of C which is soluble in an ammonia solution.

Answer

$C$ is silver chloride which is soluble in ammonia.
Pungent smelling gas B is ammonia.
White solid $A$ is ammonium chloride.
$
NH _4 Cl ( s ) \xrightarrow{ NaOH } NH _3( g )+ H _2 O + NaCl
$
$
NH _3( g ) \xrightarrow{\text { Red litmus }} \text { blue litmus }
$
$
\underset{ A }{ NH _4 Cl ( s )} \underset{ HNO _3}{ AgNO _3} AgCl ( s )
$

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Question 252 Marks

Write sqauential observation for effect of heat on Lead carbonate.

Answer

i) A white solid turns yellow on heating.
ii) Gives off a gas which extinguishes a burning wooden splinter.
iii) Gas evolved turns lime water milky.

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Question 262 Marks

Write sqauential observation for effect of heat on Copper nitrate.

Answer

i) Bluish green crystalline solid, on heating, melts to form a bluish green mass and gives off steamy vapours which condense on the cooler part of the test tube.
ii) On further heating, the bluish green mass changes to a black residue.
iii) It gives off a reddish brown gas and gives a gas which rekindles a glowing splinter, i.e. oxygen.

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Question 272 Marks

Give two tests of the following:
Water vapour

Answer

Water vapour : These are colourless vapours and are neutral to litmus. These can be tested by first condensing on the walls (cooler parts) of the test tube and then by adding anhydrous copper sulphate to the collected liquid, if the white colour of copper sulphate changes to blue, then the gas is water vapour.

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Question 282 Marks

Give two tests of the following:
Oxygen

Answer

Oxygen : It is an odourless and colourless gas and turns alkaline pyrogallol brown. It can also be tested by brining a lighted splinter near the gas, if the splinter starts glowing, the gas is oxygen.

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Question 292 Marks

Give two tests of the following:
$NH_3$

Answer

$NH_3$ It has a strong pungent smell and turns moist red litmus blue. It can also be tested by bringing a glass rod dipped in conc. HCl in contact with the gas, if the gas is ammonia then it will produce dense white fumes near the glass rod.

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Question 302 Marks

Chloride ion.

Answer

A small amount of the salt is taken in a test tube and conc. $H_2SO_4$ is added to it and then test tube is warmed, if a colourless gas with pungent odour is evolved then chloride ions are present in the salt. It can be confirmed by bringing a glass rod dipped in ammonia solution near the gas evolved, if dense white fumes are formed then presence of chloride ions is confirmed.

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