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

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Question 13 Marks

(a) What are the terms defined by the following?
(i) A salt containing a metal ion surrounded by other ions or molecules.
(ii) A base which is soluble in water.
(b) Making use only of substances chosen from those given below:
Dilute sulphuric acidSodium Carbonate
Zinc Sodium sulphite
Lead Calcium carbonate
Give equations for the reactions by which you could obtain :
(i) Hydrogen
(ii) Sulphur dioxide
(iii) Carbon dioxide
(iv) Zinc carbonate (two steps required)

Answer

(i) Complex salts
(ii) Alkali
(i) $Zn + H _2 SO _4 \longrightarrow ZnSO _4+ H _2$
(ii) $Na _2 SO _3 \longrightarrow Na _2 O + SO _2$
(iii) $Na _2 CO _3+ H _2 SO _4 \longrightarrow Na _2 SO _4+ H _2 O + CO _2$ )
(iv) $Zn + H _2 SO _4 \longrightarrow ZnSO _4+ H _2$
$
ZnSO _4+ Na _2 CO _3 \longrightarrow Na _2 SO _4+ ZnCO _3
$

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Question 23 Marks

Name the acidic anhydride of the following acids:
(i) sulphurous acid
(ii) nitric acid
(iii) phosphoric acid
(iv) carbonic acid

Answer

The anhydride of following acids are:
(i) Sulphurous acid: $SO_2$
(ii) Nitric acid: $N_2O_5$
(iii) Phosphoric acid: $P_2O_5$
(iv) Carbonic acid : $CO_2$

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Question 33 Marks

Define the term 'basicity' of an acid. Give the basicity of : nitric acid, sulphuric acid, phosphoric acid?

Answer

Basicity : The basicity of an acid is defined as the number of hydronium ions $(H_3O^+)$ that can be produced by the ionization of one molecule of that acid in aqueous solution.
The basicity of following compounds are :
Nitric acid : Basicity = $1$
Sulphuric acid : Basicity =$2$
Phosphoric acid : Basicity =$3$

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Question 43 Marks

How is an acid prepared from a Non-metal
Give an equation for it.

Answer

Acids are prepared from non-metals by their oxidation.
For example :Sulphur or phosphorus is oxidized by conc. Nitric acid to form sulphuric acid or phosphoric acid.
$S + 6HNO_3 \rightarrow H_2SO_4 + 2H_2O + 6NO_2$
$P + 5HNO_3 \rightarrow H_3PO_4 + H_2O + 5NO_2$

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Question 53 Marks

Explain the following :
$H_3PO_3$ is not a tribasic acid .

Answer

$H _3 PO _3$ is not a tribasic acid because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atoms are replaceable. Hydrogen atoms directly bonded to phosphorus atoms are not replaceable

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Question 63 Marks

Explian the following :
Dil. HCl acid is stronger than highly concentrated acetic acid.

Answer

Strength of an acid is the measure of concentration of hydronium ions it produces in its aqueous solution. Dil. HCl produces high concentration of hydronium ion compared to that of concentrated acetic acid. Thus, dil. HCl is stronger acid than highly concentrated acetic acid.

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Question 73 Marks

How can this impurity be removed?

Answer

The impurity can be removed by passing a current of dry hydrogen chloride gas through a saturated solution of the affected salt. Pure sodium chloride is produced as a precipitate which can be recovered by filtering and washing first with a little water and finally with alcohol.

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Question 83 Marks

why does common salt get wet during the rainy season?

Answer

Table salt turns moist and ultimately forms a solution on exposure to air especially during the rainy season. Although pure sodium chloride is not deliquescent, the commercial version of the salt contains impurities (such as magnesium chloride) which are deliquescent substances.

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Question 93 Marks

Distinguish between drying and dehydrating agent.

Answer

Drying agent	Dehydrating agent
(a) They remove moisture from other substances. (b) They are used to dry gases like chlorine, Sulphur dioxide. They are used in desiccators to keep substances dry. (c) They represent physical change	i. They remove chemically combined elements of water in the ratio of 2:1 from a compound. ii. They prepare substances like carbon monoxide, sugar charcoal etc. iii. They represent chemical change

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Question 103 Marks

Explain clearly how conc, $H_2SO_4$ is used as dehydrating as well as drying agent.

Answer

Conc. sulphuric acid is hygroscopic in nature and can remove moisture from other substances; therefore, it is used as a drying agent.
It is also used as a dehydrating agent because it has a strong affinity for water and thus absorbs water quickly from compounds.

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Question 113 Marks

Give reason for the following:
Anhydrous calcium chloride is used in a desiccator.

Answer

Desiccating agents are used to absorb moisture. Anhydrous calcium chloride $(CaCl_2)$ has the capacity of absorbing moisture as it is hygroscopic in nature. So, it is used in a desiccator.

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Question 123 Marks

Give reason for the following:
Sodium hydrogen sulphate is not an acid but it dissolves in water to give hydrogen ions, according to the equation
$NaHSO_4 ⇆ H^+ + Na^+ + SO_4^{2-}$

Answer

Sodium hydrogen sulphate $\left[ NaHSO _4\right]$ is an acid salt and is formed by the partial replacement of the replaceable hydrogen ion in a dibasic acid $\left[ H _2 SO _4\right]$. The $[ H ]$ atom in $NaHSO _4$ makes it behave like an acid. So, on dissolving in water, it gives hydrogen ions.

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Question 133 Marks

State your observation when the following are exposed to the atmosphere.
(a) Washing soda crystals
(b) Iron (III) chloride salts

Answer

(a) When washing soda $\left( Na _2 CO _3 \cdot 10 H _2 O \right)$ is exposed to air, it loses 9 molecules of water to form a monohydrate.
$
Na _2 CO _3 \cdot 10 H _2 O \xrightarrow{\text { air }} Na _2 CO _3 \cdot H _2 O +9 H _2 O
$
(b) It absorbs moisture from the atmosphere and becomes moist and ultimately dissolves in the absorbed water, forming a saturated solution.

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Question 143 Marks

define deliquescence. Give examples.

Answer

Water-soluble salts which on exposure to the atmosphere absorb moisture from the atmosphere and dissolve in the same and change into a solution. The phenomenon is called deliquescence and the salts are called deliquescent.
Examples: $CaCl_2, MgCl_2, ZnCl_2$

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Question 153 Marks

Define efflorescence. Give examples.

Answer

Crystalline hydrated salts which on exposure to the atmosphere lose their water of crystallisation partly or completely and change into a powder. This phenomenon is called efflorescent and the salts are called efflorescent.
Examples: $CuSO_4.5H_2O, MgSO_4.7H_2O, Na_2CO_3.10H_2O$

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Question 163 Marks

Give four substances which contain water of crystallization and write their common names.

Answer

Common name	Chemical name	Formula
Washing soda	Sodium carbonate decahydrate	$Na_2CO_3.10H_2O$
Epsom salt	Magnesium sulphate heptahydrate	$MgSO_4. 7H_2O$
Potash alum	Hydrated potassium aluminium sulphate	$K_2SO_4.Al(SO_4)_3.24H_2O$
Gypsum	Hydrated calcium sulphate	$CaSO_4.2H_2O$

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Question 173 Marks

Name the salt which on hydrolysis forms
(a) Acidic
(b) Basic acid
(c) Neutral solution. Give a balanced equation for each reaction.

Answer

(a) Iron chloride $\left( FeCl _3\right)$
$FeCl_3+3 H_2 O \rightarrow 3 HCl+Fe(OH)_3$
(b) Ammonium acetate $\left( CH _3 COONH _4\right)$
$CH_3 COONH_4+H_2 O \rightarrow CH_3 COOH+NH_4 OH$
(c) Sodium chloride
$NaCl_{(s)}+H_2 O \rightarrow Na_{(aq)}^{+} OH_{(aq)}^{-}+H_2 O$

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Question 183 Marks

The following is a list of methods for the preparation of salts.
A – direct combination of two elements
B – reaction of a dilute acid with a metal.
C – reaction of a dilute acid with an insoluble base.
D – titration of a dilute acid with a solution of soluble base.
E – reaction of two solutions of salts to form a precipitate.
Choose from the above list A to E, the best method of preparing the following salts by giving a suitable equation in each case:
1. Anhydrous ferric chloride,
2. Lead chloride,
3. Sodium sulphate.
4. Copper sulphate.

Answer

1. Anhydrous ferric chloride: - A (Direct combination of two elements)
$2 Fe+3 Cl_2 \longrightarrow 2 FeCl_3$
2. Lead chloride: - E (Reaction of two solutions of salts to form a precipitate
$Pb\left(NO_3\right)_2+2 HCl \longrightarrow PbCl_2+2 HNO_3$
3. Sodium sulphate: - D (Titration of dilute acid with a solution of soluble base)
$2 NaOH+H_2 SO_4 \rightarrow Na_2 SO_4+2 H_2 O$
4. Copper sulphate:- C (reaction of dilute acid with an insoluble base)
$Cu(OH)_2+H_2 SO_4 \rightarrow CuSO_4+2 H_2 O$

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Question 193 Marks

How would you prepare :
Calcium sulphate from calcium carbonate

Answer

Dissolving $CaCO_3$ in sulphuric acid $(H_2SO_4)$ solution, you'll get $CaSO_4$ salt
$CaCO_3 (s) + H_2SO_4 (aq) → CaSO_4 (s) + CO_2 (g) + H_2O (l)$
Calcium is a very strong reducing agent, its reduction potential is $2.87 V$. Reduction potential of Hydrogen is $0 V$
So calcium will displace hydrogen ions from suplhuric acid.

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Question 203 Marks

How would you prepare :
sodium hydrogen carbonate crystals.

Answer

Sodium hydrogen carbonate crystals :
Dissolve $5$ grams of anhydrous sodium carbonate in about 25 ml of distilled water in a flask. Cool the solution by keeping the flask in a freezing mixture. Pass carbon dioxide gas in the solution. Crystals of sodium bicarbonate will precipitate out after sometime. Filter the crystals and dry it in folds of filter paper.
Reaction : $Na_2CO_3 + CO_2 + H_2O ⟶ 2NaHCO_3$

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Question 213 Marks

Choose the most appropriate answer from $( SO_2 , SiO_2 , Al_2O3 , CO , MgO , Na_2O )$
(a) A covalent oxide of a metalloid.
(b) An oxide which when dissolved in water form acid .
(c) A basic oxide
(d) An amphoteric oxide.

Answer

a) Silicon is a metalloid. The covalent oxide is $SiO_{2}$_
b) Acidic oxide - gives acid with water - $SO_2$_
$SO_2 + H_2O ----> H_2SO_3$_
c) Basic oxide - gives base with water -$Na_2O$
$Na_2O + H_2O -----> 2 NaOH$
d) An amphoteric oxide - Shows both acidic and basic property
$Al_2O_3$

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Question 223 Marks

From the formula listed below, choose one, in each case, corresponding to the salt having the given description: $AgCl, CuCO_3, CuSO_4.5H_2O, KNO_3, NaCl, NaHSO_4, Pb(NO_3)_2, ZnCO_3, ZnSO_4,7H_2O.$

an acid salt
an insoluble chloride
on treating with concentratedsulphuric acid, this salt changes from blue to white
on heating, this salt changes from green to black
this salt gives nitrogen dioxide on heating

Answer

$NaHSO_4$
$AgCl$
$CuSO_4.5H_2O$
$CuCO_3$
$Pb(NO_3)_2$

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Question 233 Marks

Choosing only substances from the list given in the box below, write equations for the reactions which you would use in the laboratory to obtain:

Sodiumsulphate
Coppersulphate
Iron(II)sulphate
Zinc carbonate

Dilute sulphuric acid	Copper	Copper carbonate
	Iron	Sodium carbonate
	Sodium
	Zinc

Answer

$a. Na_2CO_3 + H_2SO_4 (dil) \rightarrow Na_2SO_4 + H_2O + CO_2$
$b. CuCO_3 + H_2SO_4 (dil) \rightarrow CuSO_4 + H_2O + CO_2$
$c. Fe + H_2SO_4 (dil) \rightarrow FeSO_4 + H_2$
$d. Zn + H_2SO_4 (dil) \rightarrow ZnSO_4 + H_2$
$ZnSO_4 + Na_2CO_3 \rightarrow ZnCO_3 + Na_2SO_4$

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Question 243 Marks

For each of the salt: $A, B, C$ and $D,$ suggest a suitable method of its preparation.

$A$ is a sodium salt.
$B$ is an insoluble salt.
$C$ is a soluble salt of copper.
$D$ is a soluble salt of zinc.

Answer

a. By neutralisation:
$NaOH + HCl \rightarrow NaCl + H_2O$
b. By precipitation:
$Pb(NO_3)_2 + 2NaCl \rightarrow PbCl_2 + 2NaNO_3$
$c. CuCO_3 + H_2SO_4\rightarrow CuSO_4 + H_2O + CO_2$
d. Simple displacement:
$Zn + H_2SO_4\rightarrow ZnSO_4 + H_2$

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Question 253 Marks

You are provided with the following chemicals : $NaOH, Na_2CO_3, H_2O, Zn(OH)_2, CO_2, HCI, Fe, H_2SO_4, CI_2, Zn$. Using the suitable chemicals from the given list only, state briefly how you would prepare:
(a) iron (III) chloride,
(b) sodium sulphate,
(c) sodium zincate
(d) iron (II) sulphate,
(e) sodium chloride?

Answer

(a) Iron (III) Chloride: Iron chloride is formed by direct combination of elements. $2Fe + 3Cl_2 ⟶ 2FeCI_3$
(b) Sodium sulphate: By neutralization of caustic soda with dilute sulphuric acid $2NaOH + H_2SO_4 ⟶ Na_2SO_4 + 2H_2O$
(c) Sodium zincate: By the action of metals with alkalis
$Zn + 2NaOH ⟶ Na_2ZnO_2 + H_2$
(d) Iron (II) sulphate: Iron sulphate is prepared by the action of dilute acid on an active metal. $Fe + H_2SO_4 ⟶ FeSO_4 + H_2$
(e) Sodium chloride: By the neutralization reaction of strong acid with strong base $NaOH + HCI ⟶ NaCI + H_2O$

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Question 263 Marks

Define the term neutralization, if one mole of a strong acid reacts with one mole of a strong base, the heat produced is always the same. Why?

Answer

Neutralization is the process by which $H^+$ ions of an acid react completely with the $[OH]^-$ ions of a base to give salt and water only.
Neutralization is simply a reaction between $H^+$ ions given by strong acid and $OH^-$ ions given by strong base. In case of all strong acids and strong bases, the number of $H^+$ and $OH^-$ ions produced by one mole of a strong acid or strong base is always same. Hence the heat of neutralization of a strong acid with strong base is always same.

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Question 273 Marks

Choosing only substances from the list given in the box below, write equations for the reactions which you would use in the laboratory to obtain:

Sodiumsulphate
Coppersulphate
Iron(II)sulphate
Zinc carbonate

Dilute sulphuric acid	Copper	Copper carbonate
	Iron	Sodium carbonate
	Sodium
	Zinc

Answer

Zinc Sulphate – Displacement
$Zn(OH)_2 + H_2SO_4 ⟶ ZnSO_4 + 2H_2O$
Ferrous sulphide – synthesis
$Fe + S ⟶ FeS$
Barium sulphate – Precipitation
$BaCI_2+H_2SO_4 ⟶ BaSO_4 + 2HCI$
Ferric sulphate – Oxidation
$Fe + H_2SO_4 ⟶ FeSO_4 + H_2$
Sodium sulphate – Neutralisation
$2NaOH + H_2SO_4 ⟶ Na_2SO_4 + 2H_2O$

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Question 283 Marks

When you use universal indicator, you see that solutions of different acids produce different colours. Indeed, solution of the same acid with different concentrations will also give different colours. Why?

Answer

A universal indicator is a mixture of dyes which identify a gradual change of various colours over a wide range of pH, depending on the strength of the acid. When we use a universal indicator, we see solutions of different acids produce different colours. Indeed, solutions of the same acid with different concentration give different colours.
The more acidic solutions turn universal indicator bright red. A less acidic solution will only turn it orange-yellow. Colour differences can also be observed in case of vinegar which is less acidic and battery acid which is more acidic.

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Question 293 Marks

How does tooth enamel get damaged? What should be done to prevent it?

Answer

Substances like chocolates and sweets are degraded by bacteria present in our mouth. When the p H falls to 5.5 tooth decay starts. Tooth enamel is the hardest substance in our body and it gets corroded. The saliva produced by salivary glands is slightly alkaline, it helps to increase the p H , to some extent, but tooth paste which contain basic substance is used to neutralize excess acid in the mouth.

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Question 303 Marks

Distinguish between acidity of bases and basicity of acids.

Answer

The acidity of bases and basicity of acids
The acidity of bases: The number of hydroxyl ions which can be produced per molecule of the base in aqueous solution.
Basicity of acid: The basicity of an acid is defined as the number of hydronium ions that can be produced by the ionization of one molecule of that acid in aqueous solution.

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Question 313 Marks

Distinguish between a common acid base indicator and a universal indicator.

Answer

A common acid base indicator and a universal indicator:
Acid base indicator like litmus tells us only whether a given substance is an acid or a base. Universal indicator gives an idea as to how acidic or basic a substance is. An universal indicator gives different colours with solutions of different p H values.

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Question 323 Marks

You are supplied with five solutions: $A, B, C, D$ and $E$ with Ph values as follows: $A= 1.8, B = 7, C= 8.5, D = 13$, and $E=5$
Classify these solutions as neutral, slightly or strongly acidic and slightly or strongly alkaline.
Which solution would be most likely to liberate hydrogen with:
(a) magnesium powder,
(b) powdered zinc metal. Give a word equation for each reaction.

Answer

$A =$ Strongly acidic
$B =$ neutral
$C =$ Weakly alkaline
$D =$ Strongly alkaline
$E =$ Weakly acidic
(a) Solution A (acidic solution) $+ Mg \rightarrow H_2 + Mg$ salt
(b) Solution A (acidic solution) $+ Zn \rightarrow H_2 + Zn$ salt

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Question 333 Marks

Complete the table:

Indicator	Neutral	Acidic	Alkaline
Litmus Phenolphthalein	Purple Colourless

Answer

Indicator	Neutral	Acidic	Alkaline
Litmus Phenolphthalein	Purple Colourless	Blue to red Colourless	Red to blue Pink

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