Model Question Paper — 1

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.

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

Exothermic reaction

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

(NH₄)₃PO₄

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

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.

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.

Atomic number

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

Washing soda crystals

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

Hydrogen sulphide

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

Neutralisation

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

A straight line parallel to X axis

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

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

SO₂

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

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.

Copper nitrate

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

(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]

(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.

(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.

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

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

(ii) 1. Ammonium chloride [NH₄Cl]

2. Copper

(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.

(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 $\bold{M}\bold{(OH)}_{\bold{3}}$

(i) Contains ions only

(ii) Contains only molecules

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

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

(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.

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

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

(ii) Mg + H₂SO₄ (dil.) ⟶ MgSO₄ + H₂ ↑

(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

(i) He

(ii) Li

(iii) F

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).

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.

(i) Nitrogen dioxide

(ii) Lead (II) oxide (PbO)

(iii) Pb(NO₃)₂ (Lead (II) nitrate)

(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

(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 $\bold{Al}\bold{PO}_{\bold{4}}$

(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 $\bold{CB}_{\bold{4}}$

(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).

(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).

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

(i) Displacement reaction

(ii) Decomposition Reaction

(iii) Double Displacement Reaction

(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%

(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

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

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

(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

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

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.