Model Question Paper — 1

Section A

Question 1(i)

Water is a polar covalent compound. It dissolves :

1. Sodium chloride
2. Ethyl alcohol
3. Sugar
4. All of these

Answer

All of these

Reason — Water dissolves many substances, forming aqueous solutions (water solutions). Not only solids but gases and other liquids can also dissolve in water to a large extent. For the same reason, water is called a universal solvent.

Question 1(ii)

The relationship between pressure and volume at constant temperature is given by :

1. Avogadro
2. Charles
3. Boyle
4. Henry

Answer

Boyle

Reason — According to Boyle's law volume of a given mass of a dry gas is inversely proportional to its pressure at constant temperature.

P₁V₁ = P₂V₂

Question 1(iii)

The chemical reaction in which heat is evolved is known as:

1. Endothermic reaction
2. Exothermic reaction
3. Photochemical reaction
4. Electrolytic reaction

Answer

Exothermic reaction

Reason — A chemical reaction in which heat is given out is called an exothermic reaction. It causes a rise in temperature.

Question 1(iv)

The molecular formula of ammonium phosphate is:

1. (NH₄)₃PO₄
2. [(NH₄)₂PO₄]
3. NH₄PO₄
4. NH₃PO₄

Answer

(NH₄)₃PO₄

Reason — The molecular formula of ammonium phosphate is (NH₄)₃PO₄

Question 1(v)

If an element has five electrons in its outermost shell, then it is likely to be:

1. Metallic
2. Non metallic
3. Metalloid
4. Inert gas

Answer

Non metallic

Reason — Element with five electrons in its outermost shell, will lie in 15 A group of periodic table and will be a non-metal.

Question 1(vi)

The double covalent molecule is :

1. Oxygen
2. Ammonia
3. Sodium chloride
4. Hydrogen sulphide

Answer

Oxygen

Reason — To attain the stable electronic configuration of the nearest noble gas neon, oxygen needs two electrons.
When two oxygen atoms come closer, each contributes two electrons and so they have two shared pair of electrons between them. Both atom attain an octet, resulting in the formation of a double covalent bond [O=O] between them.

Question 1(vii)

According to modern periodic law, the properties of elements are a periodic function of their:

1. Atomic volume
2. Atomic number
3. Atomic weight
4. Mass number

Answer

Atomic number

Reason — According to modern periodic law, the properties of elements are a periodic function of their atomic number.

Question 1(viii)

Which of the following will produce water vapour on heating?

1. Potassium chloride crystals
2. Sodium chloride crystals
3. Sodium nitrate crystals
4. Washing soda crystals

Answer

Washing soda crystals

Reason — Washing soda crystals (Na₂CO₃.10H₂O) contain water of crystallisation. On heating, it is given off as water vapour.

Question 1(ix)

The gas which produces a black precipitate when passed through lead acetate solution is:

1. Hydrogen sulphide
2. Ammonia
3. Sulphur dioxide
4. Hydrogen chloride

Answer

Hydrogen sulphide

Reason — When hydrogen sulphide is passed through lead acetate solution, it produces a silvery black precipitate of PbS.

Question 1(x)

When acid reacts with base to form salt and water only, the reaction is known as:

1. Displacement
2. Neutralisation
3. Decomposition
4. Redox

Answer

Neutralisation

Reason — The reaction between an acid and a base that forms salt and water only is referred to as Neutralisation reaction.

Question 1(xi)

The graph of PV vs P for a gas is:

1. Parabolic
2. Hyperbolic
3. A straight line parallel to X axis
4. A straight line passing through origin

Answer

A straight line parallel to X axis

Reason — a straight line is obtained parallel to the pressure axis.

Question 1(xii)

Which metal gives hydrogen upon reaction with all of the following - Acid, alkali, water?

1. Iron
2. Zinc
3. Magnesium
4. Lead

Answer

Zinc

Reason — Zn has a unique nature.

Zinc is considered to have a unique nature because it can react with acids and can even react with hot conc. alkalis to form hydrogen and a soluble salt.

Zn + 2HCl ⟶ ZnCl₂ + H₂

Zn + 2NaOH ⟶ Na₂ZnO₂ + H₂ ↑

Zn with water also gives hydrogen

Zn + H₂O ⟶ ZnO + H₂

Question 1(xiii)

A gas which can act as an oxidizing as well as reducing agent:

1. CO
2. NO₂
3. SO₂
4. H₂S

Answer

SO₂

Reason — Sulphur dioxide is an oxidizing as well as reducing agent.

Question 1(xiv)

Isotopes differ in number of :

1. Electrons
2. Protons
3. Neutrons
4. Positive charge

Answer

Neutrons

Reason — Isotopes are the elements having the same atomic number but different mass numbers.

For example : ²⁴₁₂Mg and ²⁶₁₂Mg

Isotopes differ in number of neutrons.

Question 1(xv)

The substance which leaves a black residue on heating is :

1. Zinc carbonate
2. Copper nitrate
3. Lead carbonate
4. Ammonium dichromate.

Answer

Copper nitrate

Reason — Copper nitrate on heating gives black residue of copper oxide and nitrogen dioxide gas along with oxygen gas are evolved.

Question 2(a)

Name the gas evolved in each of the following cases:

(i) Copper carbonate is heated strongly

(ii) Lead nitrate is heated

(iii) Nitrogen combines with hydrogen

(iv) Copper sulphate is heated strongly

(v) Addition of sodium to cold water

Answer

(i) Carbon dioxide [CO₂]

(ii) Nitrogen dioxide [NO₂] and oxygen gas [O₂]

(iii) Ammonia [NH₃]

(iv) Sulphur dioxide [SO₂] and oxygen gas [O₂]

(v) Hydrogen gas [H₂]

Question 2(b)

What do you observe when :

(i) Ammonium chloride crystals are heated in a test tube ?

(ii) Iron nails are added to copper sulphate solution ?

(iii) Lead nitrate crystals are heated strongly?

(iv) Silver nitrate solution is mixed with sodium chloride solution?

(v) Blue copper sulphate crystals are heated ?

Answer

(i) On heating ammonium chloride, white crystalline solid sublimates to form a basic gas (NH₃) and acidic gas (HCl). The dense white fumes are noticed that form a white mass on the cooler parts of the test tube. No residue is left behind.

(ii) When iron nail is kept in a blue coloured copper sulphate solution for sometime, a reddish brown coating is seen on the iron nail and the colour of the solution changes gradually from blue to light green. The reason for this observation is that iron being more reactive than copper, displaces copper from the solution and copper is deposited on the iron nail

(iii) When solid lead nitrate is heated strongly, it decomposes to produce light yellow solid lead monoxide, reddish brown nitrogen dioxide gas and colourless oxygen gas.

(iv) When silver nitrate solution is mixed with sodium chloride solution, a white ppt of silver chloride is formed along with sodium nitrate.

(v) The blue coloured hydrous copper sulphate changes to white anhydrous copper sulphate releasing water of crystallization.

Question 2(c)

(i) Define : Relative atomic mass.

(ii) Why is it necessary to balance a chemical equation ?

(iii) Calculate the percentage of nitrogen in ammonium phosphide. (At.wt. : N = 14, P = 31, O = 16)

Answer

(i) The number of times one atom of an element is heavier than $\dfrac{1}{12}$th the mass of an atom of carbon [C¹²] is known as the Relative Atomic Mass [RAM] of the element.

(ii) An equation must be balanced in order to comply with the "Law of Conservation of Matter", which states that matter is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

(iii) Molar mass of ammonium phosphide [(NH₄)₃PO₄]

= 3[14 + 4(1)] + 31 + 4(16)]

= 3[18] + 31 + 64

= 54 + 31 + 64

= 149 g

Mass of nitrogen in one mole of ammonium phosphide = 3 x 14 = 42 g

149 g of ammonium phosphide contains 42 g of nitrogen.

∴ 100 g of ammonium phosphide contains $\dfrac{42 \times 100 }{149}$ = 28.18% of nitrogen.

Question 2(d)

(i) Balance each of the following chemical equations :

1. FeCl₃ + NH₄OH ⟶ NH₄Cl + Fe(OH)₃

2. Zinc + Nitric acid ⟶ Zinc nitrate + Nitrogen dioxide + Water

(ii) Identify the substance which matches the description given below:

1. White crystalline substance which sublimes on heating.
2. The metal that cannot displace hydrogen from dilute hydrochloric acid.

Answer

(i) 1. FeCl₃ + 3NH₄OH ⟶ 3NH₄Cl + Fe(OH)₃

2. Zn + 4HNO₃ ⟶ Zn(NO₃)₂ + 2NO₂ + 2H₂O

(ii) 1. Ammonium chloride [NH₄Cl]

2. Copper

Question 2(e)

Define or explain the following terms :

(i) Absolute temperature

(ii) Valency

(iii) Ozone depletion

(iv) Electrovalent bond

(v) Atom

Answer

(i) Absolute temperature — The temperature on the Kelvin scale at which molecular motion completely ceases is called absolute zero. Absolute zero is -273°C.

(ii) Valency — Valency is the combining capacity of an atom of an element or of a radical with the atoms of other elements or radicals to form molecules.

(iii) Ozone depletion — Ozone layer depletion is the thinning of the ozone layer present in the upper atmosphere. This happens when the chlorine and bromine atoms in the atmosphere come in contact with ozone and destroy the ozone molecules

(iv) Electrovalent bond — The chemical bond formed between two atoms by transfer of one or more electrons from the atom of a metallic (electropositive) element to an atom of a non-metallic (electronegative) element is called ionic bond or electrovalent bond.

(v) Atom — An atom is the smallest particle of an element that exhibits all the properties of that element. It may or may not exist independently but takes part in every chemical reactions.

Section B

Question 3(a)

The formula of the chloride of the metal 'M' is MCl₃. State the formula of its:

(i) Carbonate

(ii) Hydroxide

Answer

(i) Formula of metal carbonate

$\text{M}^{3+} \phantom{\nearrow} \text{CO}_{3}^{2-} \\[0.5em] \overset{\phantom{3}{3}}{\text{M}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{C}}\text{O}_{3} \Rightarrow \underset{\phantom{2}{2}}{\text{M}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{C}}\text{O}_{3} \\[0.5em]$

So, we get the formula as $\bold{M}_{\bold{2}}\bold{(CO_{\bold{3}}})_{\bold{3}}$

(ii) Formula of metal hydroxide

$\text{M}^{3+} \phantom{\nearrow} \text{OH}^{1-} \\[0.5em] \overset{\phantom{3}{3}}{\text{M}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{OH}} \Rightarrow \underset{\phantom{2}{1}}{\text{M}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{OH}} \\[0.5em]$

So, we get the formula as $\bold{M}\bold{(OH)}_{\bold{3}}$

Question 3(b)

Name the kind of particles (ions or molecules) present in:

(i) Sodium chloride

(ii) Carbon tetrachloride

Answer

(i) Contains ions only

(ii) Contains only molecules

Question 3(c)

Draw the orbital structure of each of the following compounds:

(i) Water

(ii) Magnesium chloride

[At.No. : H = 1, 0 = 16, Mg = 12, Cl = 17]

Answer

(i) Orbital structure of water molecule is shown below :

(ii) Orbital structure of Magnesium chloride molecule is shown below :

Question 3(d)

Write a balanced chemical equation for each of the following reactions:

(i) Magnesium hydrogen carbonate reacts with slaked lime.

(ii) Formation of coloured precipitate.

(iii) Heating ammonium dichromate.

Answer

(i) Magnesium hydrogen carbonate reacts with slaked lime.

Mg(HCO₃)₂ + Ca(OH)₂ ⟶ MgCO₃↓ + CaCO₃↓ + 2H₂O

(ii) Formation of coloured precipitate.

3NaOH + FeCl₃ ⟶ Fe(OH)₃ [reddish brown ppt.] + 3NaCl

(iii) Heating ammonium dichromate.

$\underset{\text{[Ammonium dichromate (orange)]}}{(\text{NH}_4)_2\text{Cr}_2\text{O}_7} \xrightarrow{\space \Delta \space} \underset{\text{ [Chromic oxide(green)]}}{\text{Cr}_2\text{O}_3} + 4\text{H}_2\text{O} + \text{N}_2$

Question 4(a)

Write 2 points of comparison between Halogens and Alkali metals.

Answer

Question 4(b)

Give one equation each to show the reactions of sulphuric acid :

(i) with a metal carbonate

(ii) with a metal

Answer

(i) Na₂CO₃ + H₂SO₄ ⟶ Na₂SO₄ + H₂O + CO₂ ↑

(ii) Mg + H₂SO₄ (dil.) ⟶ MgSO₄ + H₂ ↑

Question 4(c)

(i) State Boyle's law.

(ii) Calculate the volume occupied by 2 g of hydrogen at 270°C and 4 atmosphere pressure if at STP it occupies 22.4 litres.

Answer

(i) Boyle's law — Temperature remaining constant the volume of a given mass of dry gas is inversely proportional to it's pressure.

V ∝ $\dfrac{1}{\text{P}}$ [T = constant]

(ii) Initial conditions [S.T.P.] :

P₁ = Initial pressure of the gas = 1 atm

V₁ = Initial volume of the gas = 22.4 l

T₁ = Initial temperature of the gas = 273 K

Final conditions :

P₂ (Final pressure) = 4 atm

T₂ (Final temperature) = 270°C = 270 + 273 = 543 K

V₂ (Final volume) = ?

By Gas Law:

$\dfrac{\text{P}_1\times\text{V}_1}{\text{T}_1} = \dfrac{\text{P}_2\times\text{V}_2}{\text{T}_2}$

Substituting the values :

$\dfrac{1 \times 22.4}{273} = \dfrac{4 \times \text{V}_2}{543} \\[1em] \text{V}_2 = \dfrac{543 \times 22.4}{273 \times 4} \\[1em] \text{V}_2 = \dfrac{12163.2}{1092} \\[1em] \text{V}_2 = 11.13 \text{ l} \\[1em]$

∴ Volume occupied = 11.13 l

Question 4(d)

Part of the periodic table is shown as :

Based on the above table, name the :

(i) Element with duplet

(ii) Lightest alkali metal

(iii) Halogen of period 2

Answer

(i) He

(ii) Li

(iii) F

Question 5(a)

What is an acid rain ?

Answer

The term 'acid rain' refers to all precipitations — rain, snow, fog, dew — that are more acidic than normal water (i.e., have pH less than 5.6, the pH value of normal water).

Question 5(b)

How does acid rain affect soil chemistry and water bodies?

Answer

Acid rain affects soil chemistry. It removes calcium and potassium, both the basic ingredients of soil, thus making it lose its fertility.

Acid rain has serious ecological impacts as it affects water bodies too. The water of lakes and rivers is gradually becoming acidic due to acid rain, which is affecting aquatic life.

Question 5(c)

Name the first three halogens. Give their physical state and colour.

Answer

Question 5(d)

A heavy crystalline white solid on heating in a test tube crumbles with a crackling sound and gives a reddish brown residue which changes to yellow and partly fuses with the glass and stains it yellow. A brown gas is also evolved. A glowing wooden splinter relights when held near the products evolved.

(i) Name the brown gas evolved.

(ii) What is the residue left in the test tube?

(iii) Write the formula of the crystalline white solid.

Answer

(i) Nitrogen dioxide

(ii) Lead (II) oxide (PbO)

(iii) Pb(NO₃)₂ (Lead (II) nitrate)

Question 6(a)

Distinguish between the following pairs of substances :

(i) Sodium sulphide and sodium sulphite

(ii) HCl gas and chlorine gas

Answer

(i) On addition of dil. sulphuric acid to sodium sulphide, hydrogen sulphide (H₂S) gas is evolved which can be identified by its rotten egg smell. Hydrogen sulphide gas turns moist lead acetate paper silvery black.

Na₂S + H₂SO₄ ⟶ Na₂SO₄ + H₂S ↑

On addition of dil. sulphuric acid to sodium sulphite, sulphur dioxide (SO₂) gas is evolved. Sulphur dioxide gas has a suffocating odour and turns lime water milky and potassium permanganate solution from pink to clear colourless.

Na₂SO₃ + H₂SO₄ (dil.) ⟶ Na₂SO₄ + H₂O + SO₂↑

(ii) HCl and chlorine gas

Chlorine (Cl₂) turns moist starch iodide paper blue black whereas HCl does not.

Cl₂ + 2KI ⟶ 2KCl + I₂

Starch + I₂ ⟶ Blue black colour

Question 6(b)

Al₂O₃ is the formula of Aluminium oxide. Write the formulae of :

(i) Aluminium nitrate

(ii) Aluminium phosphate

Answer

(i) Formula of aluminium nitrate

$\text{Al}^{3+} \phantom{\nearrow} \text{NO}_{3}^{1-} \\[0.5em] \overset{\phantom{3}{3}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{N}}\text{O}_{3} \Rightarrow \underset{\phantom{2}{1}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \underset{3}{\text{N}}\text{O}_{3} \\[0.5em]$

So, we get the formula as $\bold{Al}\bold{(NO}_{\bold{3}}\bold{)}_\bold{3}$

(ii) Formula of aluminium phosphate

$\text{Al}^{3+} \phantom{\nearrow} \text{PO}_{4}^{3-} \\[0.5em] \overset{\phantom{3}{3}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \overset{3}{\text{P}}\text{O}_{4} \Rightarrow \underset{\phantom{2}{1}}{\text{Al}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{P}}\text{O}_{4} \\[0.5em]$

So, we get the formula as $\bold{Al}\bold{PO}_{\bold{4}}$

Question 6(c)

The electronic configuration of three elements A, B and C are as follows :

A — 2, 8, 8, 2;

B — 2, 8, 7

C — 2, 4

(i) Which of these can form cations ?

(ii) Which of these can form anions ?

(iii) Write a formula of a covalent compound formed using these elements

Answer

(i) A will form cations as it will lose electrons to attain a stable octet.

(ii) B will form anions as it will gain electrons to attain a stable octet.

(iii) Formula of a covalent compound formed

$\text{C}^{4} \phantom{\nearrow} \text{B}^{1-} \\[0.5em] \overset{\phantom{3}{4}}{\text{C}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{B}} \Rightarrow \underset{\phantom{2}{1}}{\text{C}} \space {\searrow}\mathllap{\swarrow} \space \underset{4}{\text{B}} \\[0.5em]$

So, we get the formula as $\bold{CB}_{\bold{4}}$

Question 6(d)

(i) What do you understand by the term 'isotopes'?

(ii) Why do isotopes of an element possess identical chemical properties ?

(iii) Name the isotope of hydrogen which do not have a neutron in it.

Answer

(a) The atoms of the same element, having same atomic number (Z), but different mass number (A), are called isotopes.

​(ii) Chemical properties of isotopes of the same element are similar because chemical properties are dependent on the electronic configuration of an atom. As Isotopes have same atomic number so they have same number of electrons and hence same electronic configuration.

(iii) Protium (₁¹H).

Question 7(a)

(i) Why is it necessary to compare gases at STP ?

(ii) What are the STP conditions ?

Answer

(i) Since volume of a gas changes remarkably with change in temperature and pressure, it becomes necessary to choose standard values of temperature and pressure to which gas volumes can be referred.

(ii) The standard values chosen are 0°C or 273 K for temperature and 1 atm or 760 mm of Hg for pressure. These values are known as standard temperature and pressure (STP).

Question 7(b)

What temperature in degree centigrade would be necessary to double the volume of a gas (initially at STP), if the pressure is reduced to half ?

Answer

By Gas Law:

$\dfrac{\text{P}_1\times\text{V}_1}{\text{T}_1} = \dfrac{\text{P}_2\times\text{V}_2}{\text{T}_2}$

Substituting the values :

$\dfrac{1\times \text{V}}{273} = \dfrac{0.5\times\text{2\text{V}}}{\text{T}_2} \\[0.5em] \text{T}_2 = 0.5\times 2 \times 273\\[0.5em] \text{T}_2 = 273\text{K}$

∴ Final temperature of the gas = 273 K = 0 °C

Question 7(c)

Classify the following types of reactions:

(i) 2Al + Fe₂O₃ ⟶ Al₂O₃ + 2Fe

(ii) 2KClO₃ ⟶ 2KCl + 3O₂

(iii) BaCl₂ + Na₂SO₄ ⟶ BaSO₄ + 2NaCl

Answer

(i) Displacement reaction

(ii) Decomposition Reaction

(iii) Double Displacement Reaction

Question 7(d)

Mohr's salt has the formula (NH₄)₂SO₄.FeSO₄.6H₂O

(i) Calculate its molecular mass.

(ii) What is the percentage of Nitrogen in Mohr's salt ? (Atomic mass: N =14, H = 1, S = 32, Fe = 56, O = 16)

Answer

(a) Molar mass of Mohr's salt [(NH₄)₂SO₄.FeSO₄.6H₂O]

= 2[14 + 4(1)] + 32 + 4(16) + 56 + 32 + 4(16) + 6[2(1) + 16]

= 2[18] + 32 + 64 + 56 + 32 + 64 + 6[18]

= 36 + 32 + 64 + 56 + 32 + 64 + 108

= 392 g

(ii) Molar mass of Mohr's salt [(NH₄)₂SO₄.FeSO₄.6H₂O] = 392 g

Mass of nitrogen in one mole of Mohr's salt = 2 x 14 = 28 g

392 g Mohr's salt has mass of nitrogen = 28 g

∴ 100 g Mohr's salt will have mass

= $\dfrac{28 \times 100 }{392}$

= 7.14%

Question 8(a)

Write balanced chemical equations for the preparation of Hydrogen, when the following are used :

(i) Alkali

(ii) Non metal

Answer

(i) Hydrogen from alkali

$\text{Zn} + 2\text{NaOH} \longrightarrow \underset{\text{[sodium zincate]}}{\text{Na}_2\text{ZnO}_2} + \text{H}_2 \text{[g]}$

(ii) Hydrogen from non-metal

$\underset{\text{hot coke}}{\text{C}} + \underset{\text{steam}}{\text{H}_2\text{O}} \xrightarrow{1000 \degree \text{C}} \underset{\text{water gas}}{[\text{CO} + \text{H}_2 ]} - \Delta$

Question 8(b)

What do you understand by ozone depletion ?

Answer

Ozone layer depletion is the thinning of the ozone layer present in the upper atmosphere. This happens when the chlorine and bromine atoms in the atmosphere come in contact with ozone and destroy the ozone molecules

Question 8(c)

This question relates to the industrial manufacture of Hydrogen.

(i) Name the process.

(ii) Give the main reactions with conditions.

Answer

(i) Bosch process

(ii) The main reactions of Bosch process are :

Step I

Reaction : Production of water gas

$\underset{\text{coke}}{\text{C}} + \underset{\text{steam}}{\text{H}_2\text{O}} \xrightarrow{1000 \degree \text{C}} \underset{\text{water gas}}{[\text{CO} + \text{H}_2 ]} - \Delta$

Step II

Reaction : Reduction of steam to hydrogen by carbon monoxide

$\underset{\text{water gas}}{[\text{CO} + \text{H}_2 ]} + \underset{\text{excess steam}}{\text{H}_2\text{O}} \xrightarrow[\text{Fe}_2\text{O}_3]{450 \degree \text{C}} \text{CO}_2 + 2\text{H}_2 + \Delta$

Question 8(d)

Write half reactions for the reaction — A⁺ + B ⟶ A + B⁺ and name the following:

(i) oxidizing agent

(b) substance oxidised

(c) reducing agent.

Answer

Half reaction:

A⁺ + e^- ⟶ A (Reduction)

B ⟶ B + e^- (Oxidation)

a. A, as it is oxidizing B by accepting electrons.

b. B, as it is losing electrons.

c. B, as it is reducing A by providing electrons.