Solved 2020 Question Paper ICSE Class 10 Chemistry

SECTION I (40 Marks)

Question 1(i)

The element with highest ionization potential, is:

1. Hydrogen
2. Caesium
3. Radon
4. Helium

Answer

Helium

Reason — As ionization potential decreases down the group and increases on moving from left to right in a periodic table, hence, helium, the element on the top right most corner of the periodic table has highest ionization potential.

Question 1(ii)

The inert electrode used in the electrolysis of acidified water, is:

1. Nickel
2. Platinum
3. Copper
4. Silver

Answer

Platinum

Reason — The inert electrode used in the electrolysis of acidified water is Platinum.

Question 1(iii)

A compound with low boiling point, is:

1. Sodium chloride
2. Calcium chloride
3. Potassium chloride
4. Carbon tetrachloride

Answer

Carbon tetrachloride

Reason — Carbon tetrachloride is a covalent compound and covalent compounds have low boiling point.

Question 1(iv)

The acid which can produce carbon from cane sugar, is:

1. Concentrated Hydrochloric acid
2. Concentrated Nitric acid
3. Concentrated Sulphuric acid
4. Concentrated Acetic acid

Answer

Concentrated Sulphuric acid

Reason — Concentrated Sulphuric acid acts as a dehydrating agent as it has great affinity for water. It immediately reacts with cane sugar, removes water from it and a black spongy mass of carbon rises up.

C₁₂H₂₂O₁₁ (s) $\xrightarrow{\text{Conc. H}_2\text{SO}_4}$ 12C (s) + 11H₂O

Question 1(v)

The organic compound having a triple carbon-carbon covalent bond, is:

1. C₃H₄
2. C₃H₆
3. C₃H₈
4. C₄H₁₀

Answer

C₃H₄

Reason — C₃H₄ is an Alkyne as it follows the general formula C_nH_2n-2 and Alkynes contain a triple carbon-carbon covalent bond.

Question 1(b)

State one relevant observation for each of the following reactions:

(i) Action of concentrated nitric acid on copper.

(ii) Addition of excess ammonium hydroxide into copper sulphate solution.

(iii) A piece of sodium metal is put into ethanol at room temperature.

(iv) Zinc carbonate is heated strongly.

(v) Sulphide ore is added to a tank containing oil and water, and then stirred or agitated with air.

Answer

(i) Reddish brown fumes of nitrogen dioxide gas are liberated when copper reacts with conc. nitric acid.

(ii) Deep blue or inky blue solution is formed when excess of ammonium hydroxide is added to copper sulphate solution.

(iii) Effervescence of a gas is seen when a piece of sodium metal is put into ethanol at room temperature. The gas extinguishes a burning splint with a pop sound which confirms that the gas is hydrogen.

(iv) A residue which is yellow when hot and white when cold is formed.

(v) The ore is wetted by the oil and gets separated from the gangue in the form of froth. The impurities gets wetted by water and remain behind in the sink. Since the ore is lighter, it comes on the surface with the froth and impurities are left behind.

Question 1(c)

Write a balanced chemical equation for each of the following:

(i) Reaction of carbon powder and concentrated nitric acid.

(ii) Reaction of excess ammonia with chlorine.

(iii) Reaction of lead nitrate solution with ammonium hydroxide.

(iv) Producing ethane from bromo ethane using Zn/Cu couple in alcohol.

(v) Complete combustion of ethane.

Answer

(i) C + 4HNO₃ [conc.]⟶ CO₂ + 2H₂O + 4NO₂

(ii) 8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

(iii) Pb(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Pb(OH)₂ ↓

(iv) $\underset{\text{bromoethane}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} +\text{HBr}$

(v) 2C₂H₆ + 7O₂ [excess] ⟶ 4CO₂ + 6H₂O + Δ

Question 1(d)

(i) Draw the structural formula for each of the following:

1. 2,2 dimethyl pentane
2. methanol

(ii) Write the IUPAC name for the following compounds:

1. acetaldehyde
2. acetylene

Answer

(i)

1. 2,2 dimethyl pentane

2. Methanol

(ii)

1. IUPAC name of acetaldehyde is Ethanal.
2. IUPAC name of acetylene is Ethyne.

Question 1(e)

State one relevant reason for each of the following:

(i) Graphite anode is preferred to platinum in the electrolysis of molten lead bromide.

(ii) Soda lime is preferred to sodium hydroxide in the laboratory preparation of methane.

(iii) Hydrated copper sulphate crystals turn white on heating.

(iv) Concentrated nitric acid appears yellow, when it is left for a while in a glass bottle.

(v) Hydrogen chloride gas fumes in moist air.

Answer

(i) As graphite is unaffected by the reactive bromine vapours released at the anode hence, a graphite anode is preferred to platinum in the electrolysis of molten lead bromide.

(ii) Sodalime is preferred to sodium hydroxide in the laboratory preparation of methane since it is not deliquescent and does not attack glass.

(iii) The blue coloured hydrous copper sulphate changes to white anhydrous copper sulphate as the water of crystallization is removed on heating.

CuSO₄.5H₂O ⟶ CuSO₄ + 5H₂O

(iv) Pure nitric acid [HNO₃] is colourless and unstable and decomposes slightly even at ordinary temperatures and in the presence of sunlight.

The decomposition results in formation of reddish brown nitrogen dioxide [NO₂] which remains dissolved in the acid thus imparting a slight yellowish brown colour.

(v) Due to the high solubility of HCl gas, it fumes in moist air and forms a mist of droplets of HCl acid.

Question 1(f)

Calculate:

(i) The amount of each reactant required to produce 750 ml of carbon dioxide, when two volumes of carbon monoxide combine with one volume of oxygen to produce two volumes of carbon dioxide.

2CO + O₂ ⟶ 2CO₂

(ii) The volume occupied by 80 g of carbon dioxide at STP.

(iii) Calculate the number of molecules in 4.4 gm of CO₂.

[Atomic mass of C= 12, O=16]

(iv) State the law associated in question no. (f)(i) above.

Answer

(i) [By Lussac's law]

$\begin{matrix} 2\text{CO}& + & \text{O}_2 &\longrightarrow & 2\text{CO}_2 \\ 2 \text{ vol.} & : & 1 \text{ vol.} & \longrightarrow & 2\text{ vol.} \end{matrix}$

To calculate the amount of CO required :

$\begin{matrix}\text{CO}_2 & : & \text{CO} & \\ 2 \text{ vol.} & : & 2 \text{ vol.} \\ 750 \text{ ml} & : & \text{x} \end{matrix}$

$\therefore x = \dfrac{2}{2} \times 750 = 750 \text{ ml}$

To calculate the amount of O₂ required :

$\begin{matrix}\text{CO}_2 & : & \text{O}_2 & \\ \text{ 2 vol.} & : & 1 \text{ vol.} \\ 750 \text{ cm.}^3 & : & \text{x} \end{matrix}$

$\therefore x = \dfrac{1}{2} \times 750 = 375 \text{ ml}$

Hence, CO required is 750 ml and O₂ required = 375 ml

(ii) Gram molecular mass of CO₂ = 12 + 32 = 44 g and occupies 22.4 lit. vol.

∴ 80 g. will occupy = $\dfrac{22.4}{44}$ x 80 = 40.73 lit.

Hence, volume occupied = 40.73 lits.

(iii) Gram molecular mass of CO₂ = 12 + 32 = 44 g and contains 6.023 x 10²³ molecules.

∴ 4.4 gm. of CO₂ will contain = $\dfrac{6.023 \times 10^{23}}{44}$ x 4.4 = 6.023 x 10²² molecules.

Hence, number of molecules = 6.023 x 10²² molecules.

(iv) Gay Lussac's law is associated in the question.

Question 1(g)

Give one word or a phrase for the following statements:

(i) The chemical bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair.

(ii) Electrode used as cathode in electrorefining of impure copper.

(iii) The substance prepared by adding other metals to a base metal in appropriate proportions to obtain certain desirable properties.

(iv) The tendency of an atom to attract electrons to itself when combined in a compound.

(v) The reaction in which carboxylic acid reacts with alcohol in the presence of conc. H₂SO₄ to form a substance having a fruity smell.

Answer

(i) Single Covalent bond

(ii) Pure thin sheet of copper is used as cathode.

(iii) Alloy

(iv) Electronegativity.

(v) Esterification

Question 1(h)

Fill in the blanks from the choices given in brackets:

(i) The polar covalent compound in gaseous state that does not conduct electricity is ...............

(carbon tetra chloride, ammonia, methane)

(ii) A salt prepared by displacement reaction is ...............

(ferric chloride, ferrous chloride, silver chloride)

(iii) The number of moles in 11gm of nitrogen gas is ...............

(0.39, 0.49, 0.29) [atomic mass of N=14]

(iv) An alkali which completely dissociates into ions is ...............

(ammonium hydroxide, calcium hydroxide, lithium hydroxide)

(v) An alloy used to make statues is ...............

(bronze, brass, fuse metal)

Answer

(i) The polar covalent compound in gaseous state that does not conduct electricity is ammonia

(ii) A salt prepared by displacement reaction is Ferrous chloride

(iii) The number of moles in 11gm of nitrogen gas is 0.39

Gram molecular mass of nitrogen gas (N₂) = 2(14) = 28

28 g of nitrogen gas = 1 mole

∴ 11 g of nitrogen gas = $\dfrac{1}{28}$ x 11 = 0.39

(iv) An alkali which completely dissociates into ions is lithium hydroxide

(v) An alloy used to make statues is bronze

SECTION II (40 Marks)

Question 2(a)

The following table represent the elements and the atomic number.

With reference to this, answer the following using only the alphabets given in the table.

(i) Which element combines with hydrogen to form a basic gas?

(ii) Which element has an electron affinity zero?

(iii) Name the element, which forms an ionic compound with chlorine.

Answer

(i) Q combines with hydrogen to form a basic gas.

(ii) R has electron affinity zero as it's octet is complete and it is a stable element.

(iii) P forms an ionic compound with chlorine as it has +3 valency.

Question 2(b)

Draw the electron dot diagram for the compounds given below. Represent the electrons by (.) and (x) in the diagram.

[Atomic No.: Ca = 20, O = 8, Cl = 17, H = 1]

(i) Calcium oxide

(ii) Chlorine molecule

(iii) Water molecule

Answer

(i) Electron dot diagram of Calcium oxide is shown below:

(ii) Electron dot diagram of Chlorine molecule is shown below:

(iii) Electron dot diagram of Water molecule is shown below:

Question 2(c)

Choose the correct word which refers to the process of electrolysis from A to E, to match the description (i) to (iv):

A: Oxidation B: Cathode C: Anode D: An electrolyte E: Reduction

(i) Conducts electricity in aqueous or in molten state.

(ii) Loss of electron takes place at anode.

(iii) A reducing electrode.

(iv) Electrode connected to the positive end or terminal of the battery.

Answer

(i) Conducts electricity in aqueous or in molten state — D: An electrolyte

(ii) Loss of electrons takes place at anode — A: oxidation

(iii) A reducing electrode — B: Cathode

(iv) Electrode connected to positive end or terminal of the battery. — C: Anode

Question 3(a)

Baeyer's process is used to concentrate bauxite ore to alumina.

Give balanced chemical equations for the reaction taking place for its conversion from bauxite to alumina.

Answer

Conversion of impure bauxite to sodium aluminate:

$\underset{\text{Amphoteric oxide}}{\underset{\text{[Impure bauxite]}}{\text{Al}_2\text{O}_3.2\text{H}_2\text{O }}} + \underset{\text{Base}}{\underset{\text{[conc. soln]}}{2\text{NaOH }}} \xrightarrow{150 - 200 \degree\text{C}} \underset{\text{Salt}}{\underset{\text{[sodium aluminate]}}{2\text{NaAlO}_2}} + \underset{\text{Water}}{ \text{3H}_2\text{O}}$

Conversion of sodium aluminate to aluminium hydroxide:

$\underset{\text{[sodium aluminate]}}{\text{NaAlO}_2} + 2\text{H}_2\text{O} \xrightarrow{50 - 60 \degree\text{C}} \underset{\text{[sodium hydroxide]}}{\text{NaOH}} + \underset{\text{[aluminium hydroxide]}}{\text{Al(OH)}_3}$

Conversion of Al(OH)₃ - to pure alumina - heat on Al(OH)₃:

$\underset{\text{[aluminium hydroxide]}}{\text{2Al(OH)}_3} \xrightarrow{1100\degree\text{C}} \underset{\text{[pure alumina]}}{\text{Al}_2\text{O}_3} + \text{3H}_2\text{O}$

Precipitated Al(OH)₃ is ignited to give pure alumina [Al₂O₃]

Question 3(b)

Complete the following by selecting the correct option from the choices given:

(i) pH of acetic acid is greater than dilute sulphuric acid. So acetic acid contains ............... concentration of H⁺ ions. (greater, same, low)

(ii) The indicator which does not change colour on passage of HCl gas is ................ (methyl orange, moist blue litmus, phenolphthalein)

(iii) The acid which cannot act as an oxidizing agent is ................ (conc. H₂SO₄, conc. HNO₃, conc. HCl)

Answer

(i) pH of acetic acid is greater than dilute sulphuric acid. So, acetic acid contains low concentration of H⁺ ions.

(ii) The indicator which does not change colour on passage of HCl gas is phenolphthalein.

(iii) The acid which cannot act as an oxidizing agent is conc. HCl

Question 3(c)

Match the gases given in column I to the identification of the gases mentioned in column II:

Answer

Question 4(a)

Differentiate between the following pairs based on the information given in the brackets.

(i) Conductor and electrolyte (conducting particles)

(ii) Cations and anions (formation from an atom)

(iii) Acid and Alkali (formation of type of ions)

Answer

(i) Difference between Conductor and electrolyte (conducting particles):

(ii) Difference between Cations and anions (formation from an atom):

(iii) Difference between Acid and Alkali (formation of type of ions):

Question 4(b)

Draw the structures of isomers of pentane.

Answer

The structures of isomers of pentane are shown below:

Pentane [n-pentane]

2-Methyl butane [iso-pentane]

2,2 Dimethyl Propane [neo-pentane]

Question 4(c)

Hydrogen chloride gas is prepared in the laboratory using concentrated sulphuric acid and sodium chloride. Answer the questions that follow based on this reaction:

(i) Give the balanced chemical equation for the reaction with suitable condition(s) if any.

(ii) Why is concentrated sulphuric acid used instead of concentrated nitric acid?

(iii) How is the gas collected?

(iv) Name the drying agent not used for drying the gas.

Answer

(i) Balanced chemical equation for the reaction are :

$\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g.]}$

(ii) As conc. H₂SO₄ is non-volatile and has a high boiling point, therefore, it displaces the volatile hydrogen chloride from the salt sodium chloride. Hence, conc. H₂SO₄ is used as a reactant in the laboratory preparation of HCl from sodium chloride.
Conc. nitric acid cannot be used in place of conc. H₂SO₄ since it is volatile and may volatize out along with the hydrogen chloride.

(iii) The gas is collected by upward displacement of air method.

(iv) Quicklime (CaO) and phosphorous pentoxide [P₂O₅] are not used as drying agent, since they react with HCl forming their respective chlorides.

Question 5(a)

Distinguish between the following pairs of compounds using a reagent as a chemical test:

(i) Calcium nitrate and Zinc nitrate solution.

(ii) Ammonium sulphate crystals and Sodium sulphate crystals.

(iii) Magnesium chloride and Magnesium nitrate solution.

Answer

(i) When ammonium hydroxide (NH₄OH) is added to zinc nitrate solution [Zn(NO₃)₂], a gelatinous white ppt of zinc hydroxide [Zn(OH)₂] is obtained which is soluble in excess of NH₄OH.

$\underset{\text{colourless solution}}{{\text{ZnSO}_4}} + 2\text{NH}_4\text{OH} \longrightarrow \underset{\text{white gelatinous ppt}}{\text{Zn(OH)}_2↓} + \underset{\text{colourless in solution}}{(\text{NH}_4)_2\text{SO}_4}$

(With excess NH₄OH ppt. dissolves)

$\text{Zn(OH)}_2 + (\text{NH}_4)_2\text{SO}_4 + 2\text{NH}_4\text{OH} \longrightarrow \underset{\underset{\text{zinc (II) sulphate}}{\text{Tetraammine}}}{[(\text{Zn(NH}_3)_4]\text{SO}_4} + 4\text{H}_2\text{O}$

On the other hand, calcium nitrate solution [Ca(NO₃)₂] does not give any ppt. even when excess of ammonium hydroxide is added.

(ii) Ammonium salts react with alkalis on heating to liberate Ammonia gas. Hence, we can use NaOH as reagent to distinguish between Ammonium Sulphate crystals and Sodium Sulphate crystals. Below is the reaction for the same:

(NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃ [g]

(iii) Add silver nitrate soln. to the given solns., Magnesium chloride reacts to form a white ppt. which is soluble in NH₄OH and insoluble in dil. HNO₃. The other solution is Magnesium nitrate.

MgCl₂ + 2AgNO₃ ⟶ 2AgCl ↓ [white ppt.] + Mg(NO₃)₂

Mg(NO₃)₂ + AgNO₃ ⟶ no white ppt.

Question 5(b)

Calculate the percentage of:

(i) Fluorine

(ii) Sodium and

(iii) Aluminium in sodium aluminium fluoride [Na₃AlF₆], to the nearest whole number.

[Atomic Mass: Na = 23, Al= 27, F= 19]

Answer

(i) Molecular weight of sodium aluminium fluoride (Na₃AlF₆)
= 3(23) + 27 + 6(19)
= 69 + 27 + 114
= 210 g

210 g of sodium aluminium fluoride contains 114 g of fluorine

∴ 100 g of sodium aluminium fluoride will contain = $\dfrac{114}{210}$ x 100 = 54.28% = 54%

(ii) 210 g of sodium aluminium fluoride contains 69 g of sodium

∴ 100 g of sodium aluminium fluoride will contain = $\dfrac{69}{210}$ x 100 = 32.85% = 33%

(iii) 210 g of sodium aluminium fluoride contains 27 g of aluminium

∴ 100 g of sodium aluminium fluoride will contain = $\dfrac{27}{210}$ x 100 = 12.85% = 13%

Hence, percentage of F = 54%, Na = 33%, Al = 13%

Question 5(c)

(i) State the volume occupied by 40 gm of methane at STP, if its vapour density (V.D.) is 8.

(ii) Calculate the number of moles present in 160 gm of NaOH.

[Atomic Mass: Na = 23, H= 1, O= 16]

Answer

(i) Gram molecular mass of methane = V.D. x 2 = 8 x 2 = 16 g

16 g of methane occupies 22.4 lit.

∴ 40 g of methane will occupy = $\dfrac{22.4}{16}$ x 40 = 56 lits.

(ii) Gram molecular mass of NaOH = 23 + 16 + 1 = 40 g

40 g of NaOH = 1 mole

∴ 160 g of NaOH = $\dfrac{160}{40}$ = 4 moles.

Question 6(a)

Identify the salts P, Q, R from the following observations:

(i) Salt P has light bluish green colour. On heating, it produces a black coloured residue. Salt P produces brisk effervescence with dil. HCl and the gas evolved turns lime water milky, but no action with acidified potassium dichromate solution.

(ii) Salt Q is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt Q produces chalky white insoluble precipitate with excess of ammonium hydroxide.

(iii) Salt R is black in colour. On reacting with concentrated HCl, it liberates a pungent greenish yellow gas which turns moist starch iodide paper blue black.

Answer

(i) Copper carbonate

(ii) Lead nitrate

(iii) Manganese dioxide

Question 6(b)

Identify the substance underlined in each of the following:

(i) The electrode that increases in mass during the electro-refining of silver.

(ii) The acid that is a dehydrating as well as a drying agent.

(iii) The catalyst used to oxidize ammonia into nitric oxide.

Answer

(i) Cathode

Reason — Pure copper is deposited on the thin sheet of pure copper placed at the cathode

(ii) Sulphuric acid

Reason — Being hygroscopic sulphuric acid absorbs moisture but not enough to form a solution. Hence, it is a drying agent.

Sulphuric acid is a dehydrating agent as it can remove chemically combined water molecules from blue vitriol.

CuSO₄.5H₂O + H₂SO₄ ⇌ CuSO₄ + 5H₂O

(iii) Platinum

$4\text{NH}_3 + 5\text{O}_2 \xrightarrow[800 \degree \text{C}]{\text{Pt.}} \text{4NO} + \text{6H}_\text{2}\text{O} + \Delta$

Question 6(c)

Copy and complete the following paragraph using the options given in
brackets:

Alkenes are a homologous series of (i) ............... (saturated / unsaturated) hydrocarbons characterized by the general formula (ii) ............... (C_nH_2n/C_nH_2n). Alkenes undergo (iii)............... (addition / substitution) reactions and also undergo (iv) ............... (hydrogenation / dehydrogenation) to form alkanes.

Answer

Alkenes are a homologous series of unsaturated hydrocarbons characterized by the general formula C_nH_2n. Alkenes undergo addition reactions and also undergo hydrogentaion to form alkanes.

Question 7(a)

Write balanced chemical equations, for the preparation of the given salts.

(i) to (iii) by using the methods A to C respectively:

A: Neutralization B: Precipitation C: Titration

(i) Copper sulphate

(ii) Zinc carbonate

(iii) Ammonium sulphate

Answer

1. Preparation of copper sulphate by neutralization
   CuO + H₂SO₄ ⟶ CuSO₄ + H₂O

2. Preparation of zinc carbonate by precipitation
   Zn(NO₃)₂ + Na₂CO₃ ⟶ 2NaNO₃ + ZnCO₃

3. Preparation of ammonium sulphate by titration
   2NH₄OH + H₂SO₄ ⟶ (NH₄)₂SO₄ + 2H₂O

Question 7(b)

Name the following elements:

(i) An alkaline earth metal present in group 2 and period 3.

(ii) A trivalent metal used to make light tools.

(iii) A monovalent non-metal present in fluorspar.

Answer

(i) Magnesium

(ii) Aluminium

(iii) Fluorine

Question 7(c)

An aqueous solution of nickel (II) sulphate was electrolyzed using nickel electrodes.

Observe the diagram and answer the questions that follow:

(i) What do you observe at the cathode and anode respectively?

(ii) Name the cation that remains as a spectator ion in the solution.

(iii) Which equation for the reaction at the anode is correct?

1. Ni ⟶ Ni²⁺ + 2e^-+

2. Ni + 2e^- ⟶ Ni²⁺

3. Ni²⁺ ⟶ Ni + 2e^-

4. Ni²⁺ + 2e^- ⟶ Ni

Answer

(i) The observations at cathode and anode are:
At cathode: Ni²⁺ ions move towards cathode and are discharged as neutral Ni atoms by gain of electrons. Thus, Ni is deposited at cathode.
At anode: Diminishes in mass. Ni²⁺ ions are formed.

(ii) H⁺ ions.

(iii) Ni ⟶ Ni²⁺ + 2e^-