# Chemistry Unsolved Sample Paper Solutions ICSE Class 10

## Section-A

(i) (b) Cathode

Explanation :

Reduction is gain of electrons. Cathode is negatively charged electrode. Thus, reduction occurs on the cathode.

(ii) (a) More

Explanation :

Ionisation energy is the energy required to remove loosely bonded electron from outermost shell of an isolated gaseous atom. In first ionisation energy, electron from a neutral atom is removed but for second ionisation, electron is removed from a positive atom, where electron are more tightly bounded due to increased attraction force. Therefore, second ionisation energy is high relative to first IP.

(iii) (c) CO2 gas
Explanation :

In electrolytic reduction of alumina, oxygen is produced at anode. This oxygen oxidizes anode (which is made up of graphite) to initially give carbon monoxide, which when further combines with oxygen produces carbon dioxide gas.

(iv) (a) Ionic solid

Explanation :

Ionic solids contain ions in their crystal lattice which are held together by strong electrostatic forces of attraction. Due to this strong forces of attraction, ionic solids are hard and have high melting and boiling points. Most ionic compounds tend to dissociate in polar solvents due to the opposite charges on each ion.

(v) (a) Sodium chloride

Explanation :

Sodium chloride is formed by base NaOH and an acid hydrochloric acid.

(vi) (a) White ppt. soluble in excess of alkali

Explanation :

When lead nitrate is treated with sodium hydroxide solution, a white ppt. is obtained which is soluble in excess of alkali.

(vii) (c) 44

Explanation :

Molecular mass = Vapour density × 2
= 22 × 2 = 44 g

(viii) (a) Lowers; pressure

Explanation :

The HCl gas present inside the flask, when mixed with water, lowers the pressure inside the flask as some gas molecules dissolve in water.

(ix) (b) Platinum is costly and can be easily poisoned

Explanation :

Platinum is an efficient catalyst, but it is costly and easily poisoned by arsenic oxide. V2O5 is an efficient catalyst and less expensive than platinum and hence, is a suitable replacement for platinum.

(x) (d) Pink

Explanation :

Phenolphthalein is an colourless indicator which is colourless in acidic medium but turns pink in alkaline medium.

(xi) (a) NO and NO2

Explanation :
Both dilute and concentrated nitric acid reacts with copper to give salt of copper nitrate and water. However, both of these acids produce different gases. With conc. HNO3, copper reacts to form copper nitrate and nitrogen dioxide.
Cu + 4HNO3(conc.) → Cu(NO3)2 + 2NO2 + 2H2O

With dilute nitric acid, copper reacts to form copper nitrate and nitric oxide.

3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO + 4H2O

(xii) (d) 26

Explanation :
The compounds containing triple bond are known as alkynes and they have the general formula of CnH2n– 2. Where, n is the number of atoms in one molecule. If the number of hydrogen atoms in its molecule is 50, then the number of carbon atoms should be 26 (2n – 2 = 50). Therefore, n = 26.

(xiii) (b) Methoxy methane

Explanation :
The IUPAC name of dimethylether (CH3 – O – CH3) is methoxymethane.

(xiv) (c) Oxidation takes place at cathode

Explanation :

During electrolysis, oxidation i.e., loss of electrons takes at the anode.

(xv) (d) 4

Explanation :

Element with atomic number 14 is silicon, it is placed in period 4.

(i) (a) Substance B is anhydrous (fused) calcium chloride (CaCl2).

(b) Anhydrous calcium chloride absorbs the moisture present in the apparatus. This helps in keeping the anhydrous ferric chloride dry as it is a highly deliquescent salt.

(c) Iron (III) chloride should be stored in a closed container because of its deliquescent nature. In the presence of moisture, iron (III) chloride absorbs water, gets dissolved in it and forms a saturated solution.

(d) When dried chlorine gas is passed over heated iron, it forms anhydrous iron (III) chloride.2Fe + 3Cl2 — 2FeCl3

Anhydrous iron (III) chloride

(e) Substance X is conc. sulphuric acid.

(ii) 1. (C) Sodium hydrogen sulphate

2. (A) Ferrous ammonium sulphate

3. (E) Contains ions and  molecules

4. (B) Contains only ions

5. (D) Contains only molecules

(iii) (a) Increases

(b) Covalent

(c) Acids

(d) Hydrogen

(e) Methanol

(iv) (a) Ethyne do not react with Fehling’s reagent. Fehling’s reagent is used to detect the aldehydic functional groups in compounds.

(b) When hydrogen chloride gas is passed through a silver nitrate solution, a white precipitate of silver chloride is formed. which is soluble in excess of ammonium hydroxide.

(c) When sodium hydroxide is added drop wise until in excess to a solution of zinc sulphate it is observed that white precipitate is formed which is soluble in excess of sodium hydroxide.

(d) When ammonium hydroxide solution is added to iron (II) chloride, it forms a dirty green precipitate of iron (II) hydroxide which after some time turns into a reddish-brown colour.

(e) When sugar crystals are added to a hard glass test tube containing concentrated sulphuric acid charring of sugar takes place which means that sugar crystals burn in conc sulphuric acid producing brown carbon residue and smell of caramel carbon.

(v) (a)

(b) (1) The naturally occurring compounds of elements are known as mineral. It has a definite chemical composition and ordered atomic structure.

(2) Compounds having the same molecular formula, but different structural formula, are called ‘isomers’ of one another and this phenomenon is called ‘isomerism’.

## Section-B

(i) (a) Nitrate ion, NO3
(b) Sulphate ion, SO42–

(ii) (a) Oxygen gas

(b) Carbon dioxide gas

(iii) (a) Li > Na > K

(b) F < Cl < Br < I

(c) Rb > K > Li

(iv) (a) Ammonia

(b) Ferric chloride

(c) Hygroscopic

(i) (a) Aluminium

(b) Iron

(ii)

 Element Mass% Atomic weight Relative number of atoms Simple ratio Hydrogen 2.47 1 2.47 2 Phosphorus 38.25 31 1.23 1 Phosphorus 38.25 31 1.23 1 Oxygen 59.28 16 3.70 3
(a) Empirical formula – H2PO3

(b) Vapour density = 81

Molecular weight = 2 × Vapour density

= 2 × 81 = 162

Empirical weight = (1 × 2 + 31 + 16 × 3) = 81

n = Molecular weight / Empirical weight

=162/81=2

Molecular formula = (Empirical formula)n

= (H2PO3)2 = H4P2O6

(iii) (a) Quick lime. (CaO is a hydroscopic salt as it readily absorbs moisture)

(b) By downward displacement of air.

(c) Ammonia gas is not collected over water because it is highly soluble in water.

(iv) (a) When ethanol is heated with conc. H2SO4 at 170°C, it undergoes dehydration and forms ethene.

(ii)

$$\text{C}_2\text{H}_5\text{OH}\xrightarrow[170 \text{\textdegree} \text{C}]{\text{Conc}.\text{H}_2\text{SO}_4}\text{H}_2\text{C} = \text{CH}_2 + \text{H}_2\text{O}\\\text{\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space Ethene}$$

(b) When silver nitrate solution is added to dilute hydrochloric acid, an insoluble white precipitate of silver chloride is formed.

AgNO3 + HCl → AgCl↓ + HNO3

Silver chloride ppt.

(c) When zinc sulphide is heated with dilute hydrochloric acid, a colourless hydrogen sulphide gas is evolved, which has a rotten egg smell.

$$\text{ZnS}+ 2\text{HCl} \xrightarrow{\Delta}\text{ZnCl}_2 + \text{H}_2\text{S}\uarr\\\text{\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space Hydrogen sulphide gas}$$

(i) (a) When few drops of purple colour potassium permanganate is added to ethane, its purple colour does not fades but when a few drops of it is added to ethene, the solution decolourizes.

(b) Sulphuric acid precipitates the insoluble sulphate from lead nitrate solution.

Pb(NO3)2 + H2SO4 → PbCO4 + 2HNO3

Lead nitrate reacts with hydrochloric acid to give a white ppt. of lead chloride.

Pb(NO3)2 + 2HCl → PbCl2 + 2HNO3

(ii) (a) Copper sulphate and iron (II) sulphate

When little NH4OH is added to CuSO4, pale blue or bluish white precipitate appears which
dissolves in excess of NH4OH to give deep blue or inky blue solution.
CuSO4 + 2NH4OH → Cu(OH)2↓ + (NH4)2SO4

Pale blue ppt.

Cu(OH)2 + 4NH4OH → [Cu(NH3)4](OH)2 + 4H2O

Inky blue solution

When little NH4OH is added to FeSO4, dirty green precipitate appears which turns reddish brown after sometime. It is insoluble in excess of NH4OH.
FeSO4 + 2NH4OH → Fe(OH)2↓ + (NH4)2SO4

Dirty green ppt.

(b) Zinc nitrate and lead nitrate.

When little NH4OH is added to Zn(NO3)2, a white precipitate appears which is soluble in excess of NH4OH.
Zn(NO3)2 + 2NH4OH → Zn(OH)2↓ + 2NH4NO3

white ppt.

Zn(OH)2 + 4NH4OH → [Zn(NH3)4](OH)2 + 4H2O

Soluble salt

When little NH4OH is added to Pb(NO3)2 a white precipitate appears which is insoluble in excess of NH4OH.
Pb(NO3)2 + 2NH4OH → Pb(OH)2↓ + 2NH4NO3

white ppt.

(iii) (a) Hydration

(b) Pyrolysis

(c) Polymerisation

(iv) (a) Those metals which react with both alkalies as well as acids are called amphoteric metals e.g. Zn, Sn, Al etc. They react with caustic alkalies like NaOH, KOH on heating and liberates H2 gas. e.g.
Zn + 2NaOH (aq) → Na2ZnO2 + H2

Zinc (Conc.) Sodium zincate

Zn + 2KOH (aq) → K2ZnO2 + H2

Zinc (Conc.) Potassium zincate

Sn + 2NaOH(aq) + H2O → Na2SnO3 +2 H2

Tin (Conc.) Sodium stannate

Sn + 2KOH(aq) + H2O → K2SnO3 + 2 H2

Tin (Conc.) Potassium stannate

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

Aluminium Sodium aluminate

2Al + 2KOH + 2H2O → 2KAIO2 + 3H2

(ii) Those oxides which react with both acids as well as bases are called amphoteric oxides. Oxides of amphoteric metals like Zn, Sn, Al, etc., react with strong alkalies like NaOH to form complex salt and water, e.g.

ZnO + 2NaOH (aq) → Na2ZnO2 + H2O

Zinc oxide (Conc) Sodium zincate

SnO2 + 2NaOH (aq) → Na2SnO3 + H2O

Tin oxide (Conc.) Sodium stannate

Al2O3 + 2NaOH (aq) → 2NaAlO2 + H2O

Aluminium (Conc.) Sodium aluminate

oxide

(iii) Concentrated sulphuric acid act as drying agent.

(i) (a)

 Element Mass% Atomic weight Relative number of atoms Simple ratio C 85.7% 12 7.14 7.14/7.14=1 H 14.3% 1 14.3 14.3/7.14=2
(b) Empirical formula CH2.

Molecular Formula = n × Empirical formula

n = Molecular wt./Empirical formula wt.
= 28/14
= 2

Molecular formula = 2 × (CH2) = C2H4.
(ii) Empirical formula weight of X2Y = 2 × 10 + 5 = 25

Molecular weight = 2 × Vapour density

= 2 × 25 = 50

n = Molecular weight /Empirical weight

= 50/25
= 2

Molecular formula = (X2Y)2 = X4Y2
(iii) (a)  S(s) + 6HNO3(aq) → 2H2O(l) + H2SO4(aq) + 6NO2(g)

Sulphur Nitric acid Water Sulphuric acid Nitrogen dioxide

(b) The equation for catalytic oxidation of ammonia is :

$$4\text{NH}_3 + 5\text{O}_2 \xrightarrow[\text{700 – 800} \text{\textdegree}\text{C}]{\text{pt}}4\text{NO} + 6\text{H}_2\text{O} + \text{Heat}$$

Ammonia Nitric oxide

Catalyst is a wire mesh consisting of platinum and rhodium.

$$\text{KNO}_3\text{(s)} + \text{H}_2\text{SO}_4\text{(l)} \xrightarrow{(\text{T} < 200\text{\textdegree}\text{C})} \text{HNO}_3\text{(l)} + \text{KHSO}_4\text{(s)}$$

Potassium nitrate Conc. sulphuric acid Nitric acid Potassium hydrogen sulphate

(iv) (a) The equation for the laboratory preparation of hydrogen chloride gas :

$$\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{<200\text{\textdegree}\text{C}}\text{NaHSO}_4 + \text{HCl}\uarr$$

Although it is a reversible reaction, it goes to completion as hydrogen chloride continously escapes as a gas.

The reaction can occur up to the stage of the formation of sodium sulphate on heating above 200°C.

$$\text{NaHSO}_4 + \text{NaCl} \xrightarrow{\text{above} 200\text{\textdegree}\text{C}}\text{Na}_2\text{SO}_4 + \text{HCl}\uarr$$

(b) The drying agent used in the laboratory preparation of hydrochloride acid is conc. sulphuric acid. The other drying agents such as phosphorus pentoxide (P2O5) and quick lime (CaO) cannot be used because they react with hydrogen chloride.

2P2O5 + 3HCl → POCl3 + 3HPO3
CaO + 2HCl → POCl3 + 3HPO3

(c) A safety precaution which should be taken during the preparation of hydrochloric acid : Always wear chemical splash goggles, chemical-resistant gloves and a chemical resistant apron in the laboratory during the preparation of hydrochloric acid.

(i)

 Element Percentage Molecules Simple ratio Simple whole ratio C 85.7% 82.76/12=6.89 6.89/6.89=1 2 H 17.24 17.24/1=17.24 17.24/6.89=2.5 5

Empirical formula = C2H5

Empirical formula mass = (12 × 2) + (1 × 5)

= 24 + 5 = 29

Vapour density → 29 (Given)

Molecular mass = V.D. × 2 = 29 × 2 = 58 g

Molecular formula mass = n × Empirical formula mass

n = Molecular Formula mass/ Empirical Formula mass

=58/29=2

Molecular formula = n × Empirical formula

= 2 × C2H5
= C4H10

(ii) (a) But–1–ene

(b) 2-Methyl propane

(iii) (a) Electrode on the left side is the oxidising electrode because copper atoms lose electrons at this electrode, therefore, it is called as anode.

(b) At anode: Cu – 2e → Cu2+
At cathode: Cu2+ + 2e– → Cu

(c) 1. Reddish brown copper metal is deposited at cathode so anode becomes thin and cathode grows thick gradually.

2. Blue colour of aqueous copper (II) sulphate solution remains unchanged because the effective concentration of copper ions in solution remains the same.

(iv) (a) Calcium nitrate and Zinc nitrate solutions can be distinguish by reacting with ammonium hydroxide solution :

On adding ammonium hydroxide gelatinous white precipitates of zinc hydroxide are formed.

Although it is a reversible reaction, it goes to completion as hydrogen chloride continously escapes as a gas.

Zn(NO3)2 + 2NH4OH → Zn(OH)2↓ + 2NH4NO3

Zinc hydroxide

(Gelatinous white precipitate)

On adding excess of ammonium hydroxide, the precipitates dissolve forming a soluble complex.

Zn(NO)2 + 2NH4NO3 → 2NH4OH [Zn(NH3)4] (NO3)2 + 4H2O

No visible reaction occurs when we add calcium nitrate to ammonium hydroxide.

CaNO3 + NH4OH → No reaction
(b) Ammonium sulphate crystals give pungent colourless gas ammonia (NH3) when heated with any alkali or base. When NH3 gas comes in contact with a glass rod dipped in HCl white fumes of this released NH4Cl are produced. While there is no reaction with sodium sulphate or no pungent gas is released

(c) Magnesium chloride reacts with silver nitrate solution and form a white precipitate of silver chloride, whereas magnesium nitrate does not react with silver nitrate solution.

MgCl2 (aq) + 2AgNO3 (aq) → Mg(NO3)2 (aq) + 2AgCl (s)↓ Silver chloride (white precipitate)
MgNO3 + AgNO3 → No reaction

(i) (a) Compound XY2 has ionic bonds in nature because it is formed by transfer of electrons,

Four properties of compound XY2 are :

1. It is hard and brittle.

2. It is soluble in water.

3. It has high melting and boiling point.

4. It does not conduct electric current in the solid state but conducts electric current in the molten or dissolved state.

(b) In the first step the donor atom (say A) transfers one electron of its lone pair to the acceptor atom (say B). Due to this the atom A develops a unit positive charge and atom B develops a unit negative change. This charge is known as formal charge and is similar to the formation of an ionic bond. In the second step the two electrons, one each with A+ and B– are shared by both the ions. This is similar to the formation of covalent bond.

A+ + B- → A : B or A → B

Thus, a coordinate bond is equivalent to a combination of an electrovalent bond and a covalent bond. Hence, it is also called a semi polar bond or dative bond.

(ii) (a) The pH of :

1. Pure water is 7

2. Milk is 6.6

3. Human blood is 7.3

(b) pH value = 7 indicates a neutral solution.

pH value > 7 indicates an alkaline solution.

pH value < 7 indicates an acidic solution.

(iii) (a) Reduction

(b) Oxidation

(c) Reduction

(iv) 1. Thallium

2. Boron

3. Three

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