Question 1

Question 1(ii)During an endothermic reaction:The temperature of surroundings increases.The temperature of surroundings decreasesThe heat in the surroundings increasesThe reactants melt.

Accepted Answer

The temperature of surroundings decreasesReason — Heat is absorbed during an endothermic reaction, hence the temperature of the surrounding will decrease.

Question 2

Question 1(iv)When hydrochloric acid is added to silver chloride solution:No reaction takes place.A white precipitate is formed.A white solution is obtained.A reddish brown precipitate is formed.

Accepted Answer

No reaction takes place.Reason — HCl + AgCl ⟶ no reactionAs the anion of both the reacts is same hence, no reaction is possible to form new products.

Question 3

Question 1(vi)The atomic numbers of elements A, B, C and D are 2, 6, 12 and 20 respectively. Which of them has 2 electrons in its N shell?ADBC

Accepted Answer

DReason — The electronic configuration of D[20] = [2,8,8,2]. Hence, it has 2 electrons in its N shell.

Question 4

Question 1(ix)When an oxygen ion is converted to an oxygen atom, it undergoes:ReductionRedox reactionOxidationCombination reaction

Accepted Answer

OxidationReason — When an oxygen ion O-2 having electronic configuration [2,8] is converted to an oxygen atom O having electronic configuration [2,6], it loses two electrons and hence undergoes oxidation.

Question 5

Question 2(a)You are provided with a Periodic Table below :(i) What is this Periodic table known as?(ii) Give the Periodic Law for the above Periodic table.(iii) From the above Periodic table, predict the formula for the (i) oxide and (ii) hydride of Sulphur (S).(iv) State one defect of this table.(v) What is the basis of the Modern periodic table?

Accepted Answer

(i) The table is known as Mendeleev's periodic table.(ii) The Periodic Law for the above periodic table is that physical and chemical properties of elements are a periodic function of their atomic masses.(iii) (i) SO3(ii) SH2(iv) One defect of this table was the grouping of chemically dissimilar elements. Elements such as copper and silver bear no resemblance to alkali metals (lithium, sodium, etc.) but they have been placed together in the first group.(v) Modern periodic table is based on the Modern Periodic Law which states that — Physical and chemical properties of elements are periodic function of their atomic number.

Question 6

Question 2(b)Match the column A with column B:Column AColumn B(i)	HydrogenA. Alkali metal(ii) Boyle's lawB. Group I(iii) SO2C. P-V relationship(iv) SodiumD. Lead nitrate solution(v) Hydrogen sulphideE. Produced by burning coal

Accepted Answer

Column AColumn B(i)	HydrogenB. Group I(ii) Boyle's lawC. P-V relationship(iii) SO2E. Produced by burning coal(iv) SodiumA. Alkali metal(v) Hydrogen sulphideD. Lead nitrate solution

Question 7

Question 2(c)Complete the following sentences by choosing the correct answer from the bracket:(i)	The element below sodium in the Periodic Table is ............... , reactive than sodium. (more/less)(ii) ............... is a gas having a triple bond (Nitrogen/Ammonia)(iii) The average kinetic energy of the molecules of the gas is proportional to the ............... (absolute temperature/pressure)(iv) If temperature is reduced to half, ............... would also reduce to half provided pressure remains constant. (volume/pressure)(v) Ozone depletion is mainly caused by the active ............... atoms generated from	CFC in the presence of UV radiation. (chlorine/fluorine)

Accepted Answer

(i)	The element below sodium in the Periodic Table is more, reactive than sodium.(ii) Nitrogen is a gas having a triple bond.(iii) The average kinetic energy of the molecules of the gas is proportional to the absolute temperature.(iv) If temperature is reduced to half, volume would also reduce to half provided pressure remains constant.(v) Ozone depletion is mainly caused by the active chlorine atoms generated from CFC in the presence of UV radiation.

Question 8

Question 2(d)(i) 20 g of	NaCl is dissolved in 200 g of water. Calculate its concentration.(ii) In order to make the concentration of alcohol 25%, how much alcohol is to be added to 150 cm3 of water?(iii) Solubility of a substance at 45°C is 36.5g. What is meant by this statement?

Accepted Answer

(i) Given,solute = 20 gsolvent = 200 gconcentration = ?Concentration of solution = Mass of soluteMass of solute + Mass of solvent\dfrac{	ext{Mass of solute}}{	ext{	ext{Mass of solute + Mass of solvent}}}Mass of solute + Mass of solventMass of solute​ x 100Concentration of solution = 20200 + 20\dfrac{20}{	ext{200 + 20}}200 + 2020​ x 100= 9.09%Hence, concentration = 9.09%(ii) Given,concentration = 25%solvent = 150 cm3solute = ?Concentration of solution = Volume of soluteVolume of solute + Volume of solvent\dfrac{	ext{Volume of solute}}{	ext{	ext{Volume of solute + Volume of solvent}}}Volume of solute + Volume of solventVolume of solute​ x 10025100\dfrac{25}{100}10025​ = Volume of solute (x)Volume of solute (x)+ 150 \dfrac{	ext{Volume of solute (x)}}{	ext{	ext{Volume of solute (x)+ 150 }}}Volume of solute (x)+ 150 Volume of solute (x)​14\dfrac{1}{4}41​ = Volume of solute (x)Volume of solute (x)+ 150 \dfrac{	ext{Volume of solute (x)}}{	ext{	ext{Volume of solute (x)+ 150 }}}Volume of solute (x)+ 150 Volume of solute (x)​4x = x + 1503x = 150x = 50 cm3Hence, alcohol added = 50 cm3(iii) Solubility of a substance at 45°C is 36.5g means that 36.5g of substance dissolves in 100 g of water at the temperature of 45°C.

Question 9

Question 2(e)(i) Give a balanced chemical equation for each of the following:Reaction with one reactant forming three products.Reaction with two reactants forming two products.Reaction with two reactants forming three products.(ii) Give a balanced chemical equation for the following word equation:Potassium dichromate reacts with sulphuric acid and sulphur dioxide to form potassium sulphate, chromium (III) sulphate and water.

Accepted Answer

(i) Balanced chemical equation :2Pb(NO3)2 → Δ \xrightarrow{\space \Delta \space} Δ ​ 2PbO + 4NO2 + O2C2H5Br + NaOH ⟶ C2H5OH + NaBr6CO2 + 12H2O ⟶ C6H12O6 + 6H2O + 6O2(ii) K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O

Question 10

Question 3(a)How will you distinguish between the following:(i)	Carbon dioxide gas and sulphur dioxide gas.(ii) Hydrogen gas and hydrogen chloride gas?

Accepted Answer

(i)	Carbon dioxide gas has no effect on acidified potassium permanganate (KMnO4) and acidified potassium dichromate (K2Cr2O7) solution whereas sulphur dioxide gas turns acidified potassium permanganate from pink to clear colourless and acidified potassium dichromate from orange to clear green.2KMnO4 + 2H2O + 5SO2 ⟶ K2SO4 + 2MnSO4 + 2H2SO4K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O(ii) Hydrogen gas burns with a 'pop' sound in air whereas hydrogen chloride forms a curdy white ppt. on passage through AgNO3 solution. The precipitate dissolves in excess of NH4OH.

Question 11

Question 3(c)(i) Name the process used to manufacture Hydrogen.(ii) Write all the reactions involved (with proper conditions).

Accepted Answer

(i) Bosch process(ii) Reactions of Bosch process (with proper conditions):Step IReaction : Production of water gasChot coke+H2Osteam→1000°C[CO+H2]water gas−Δ\underset{	ext{hot coke}}{	ext{C}} + \underset{	ext{steam}}{	ext{H}_2	ext{O}} \xrightarrow{1000 \degree 	ext{C}} \underset{	ext{water gas}}{[	ext{CO} + 	ext{H}_2 ]} - \Deltahot cokeC​+steamH2​O​1000°C​water gas[CO+H2​]​−ΔReactants : White hot coke and steamTemperature : Around 1000°CProcess : Passage of steam over white hot coke [carbon]Chamber : Specially designed convertorStep IIReaction : Reduction of steam to hydrogen by carbon monoxide[CO+H2]water gas+H2Oexcess steam→Fe2O3450°CCO2+2H2+Δ\underset{	ext{water gas}}{[	ext{CO} + 	ext{H}_2 ]} + \underset{	ext{excess steam}}{	ext{H}_2	ext{O}} \xrightarrow[	ext{Fe}_2	ext{O}_3]{450 \degree 	ext{C}} 	ext{CO}_2 + 2	ext{H}_2 + \Deltawater gas[CO+H2​]​+excess steamH2​O​450°CFe2​O3​​CO2​+2H2​+ΔReactants : Water gas and excess steamTemperature : Around 450 °CCatalysts : Iron [III] oxide [Fe2O3], promoter chromic oxide [Cr2O3]Process : Excess steam is mixed with water gas, passed over a catalyst at elevated temperature.[CO is converted to CO2 with a further yield of hydrogen.]Step IIIReactions : Separation of carbon dioxide and carbon monoxide from the above mixture(a) CO2 is removed by dissolving mixture in water under pressure [30 atmospheres], or caustic potash solution to dissolve CO2.2KOH + CO2 ⟶ K2CO3 + H2O(b) CO is removed by dissolving mixture in ammoniacal cuprous chloride solution.CuCl + CO + 2H2O ⟶ CuCl.CO.2H2O.Thus, hydrogen gas is left over.

Question 12

Question 4(a)Define Charles' law. Give its mathematical expression.

Accepted Answer

Charles law states that pressure remaining constant, the volume of a given mass of dry gas increases or decreases by 1273\dfrac{1}{273}2731​ of its volume at 0°C for each 1°C increase or decrease in temperature, respectively.Mathematical expression of Charles' law :Suppose, a gas occupies V1 cm3 at T1 temperature and V2 cm3 at T2 temperature, then by Charles' law:    V1 α T1or V1 = kT1 (k is constant)or V1T1\dfrac{	ext{V}_1}{	ext{T}_1}T1​V1​​ = k and    V2 α T2or V2T2\dfrac{	ext{V}_2}{	ext{T}_2}T2​V2​​ = k∴ V1T1\dfrac{	ext{V}_1}{	ext{T}_1}T1​V1​​ = V2T2\dfrac{	ext{V}_2}{	ext{T}_2}T2​V2​​ = k (at constant pressure)

Question 13

Question 4(c)Give a balanced chemical equation for the following :(i)	Exothermic reaction that is also a combination reaction.(ii) A decomposition reaction involving salt of zinc.(iii) A double decomposition reaction where a white precipitate is formed.

Accepted Answer

(i) When carbon burns in oxygen to form carbon dioxide, lot of heat is produced. It is also a combination reaction.C + O2 ↑ ⟶ CO2 ↑ + Heat(ii) Zinc carbonate decomposes to form zinc oxide and releases carbon dioxide gas.ZnCO3 → Δ \xrightarrow{\space \Delta \space} Δ ​ ZnO + CO2 ↑(iii) Formation of white precipitate of silver chloride on mixing sodium chloride solution and silver nitrate solution is a double decomposition reaction.AgNO3 + NaCl ⟶ AgCl ↓ + NaNO3

Question 14

Question 4(d)Define a redox reaction. Give an equation and in it indicate the substance being oxidised and the substance being reduced.

Accepted Answer

A chemical reaction which involves, oxidation of one substance and reduction of other substance is called a Redox Reaction.Considering the reaction of Zinc with copper sulphate:Zn + CuSO4 ⟶ ZnSO4 + CuZn + Cu2+SO42- ⟶ Zn2+SO42- + CuHere, Zinc is oxidised and Copper is reduced.Oxidation — Zn - 2e- ⟶ Zn2+Reduction — Cu2+ + 2e- ⟶ Cu

Question 15

Question 5(b)(i) What is the function of ozone in atmosphere ?(ii) Name a salt whose solubility first increases and then decreases on increasing the temperature.

Accepted Answer

(i) The ozone layer acts as a blanket in the atmosphere above 16 km from the earth’s surface. Ozone absorbs the harmful ultra-violet rays coming from the sun and prevents them from reaching the earth’s surface. Thus, it protects the life on earth from harmful effects of ultra-violet rays that can cause skin cancer and destroy many organisms necessary for life in general.(ii) Hydrated Calcium Sulphate [CaSO4.2H2O]

Question 16

Question 5(c)It is found that on heating a gas, its volume increases by 50% and pressure decreases to 60% of its original value. If the original temperature was -15°C, find the temperature to which it was heated?

Accepted Answer

Initial conditions [S.T.P.] :P1 = Initial pressure of the gas = PV1 = Initial volume of the gas = VT1 = Initial temperature of the gas = -15°C = -15 + 273 = 258 KFinal conditions :P2 (Final pressure) = pressure decreases to 60% of its original value= 60100\dfrac{60}{100}10060​ of P= 35\dfrac{3}{5}53​PV2 (Final volume) = volume increases by 50% of its original value= 1 + 50100\dfrac{50}{100}10050​ of V= 100+50100\dfrac{100 + 50}{100}100100+50​ of V= 150100\dfrac{150}{100}100150​ of V= 32\dfrac{3}{2}23​VT2 (Final temperature) = ?By Gas Law:P1×V1T1=P2×V2T2\dfrac{\text{P}_1\times\text{V}_1}{\text{T}_1} = \dfrac{\text{P}_2\times\text{V}_2}{\text{T}_2}T1​P1​×V1​​=T2​P2​×V2​​Substituting the values :PV 258=35P×32VT2T2=3×3×2585×2=232210T2=232.2K\dfrac{\text{PV }}{258} = \dfrac{\dfrac{3}{5} \text{P}\times\dfrac{3}{2}\text{V}}{\text{T}_2} \[1em] \text{T}_2 = \dfrac{3\times 3\times 258}{5 \times 2} = \dfrac{2322}{10} \[1em] \text{T}_2 = 232.2 \text{K} \[1em]258PV ​=T2​53​P×23​V​T2​=5×23×3×258​=102322​T2​=232.2K∴ Final temperature of the gas = 232.2 - 273 = -40.8°C

Question 17

Question 5(d)(i) What causes the violence associated with torrential rain?(ii) Which property of water enables it to modify the climate?(iii) Explain why distilled water tastes flat.

Accepted Answer

(i) The sudden release of latent heat of condensation causes the violence associated with torrential rain.(ii) Due to it's high specific heat capacity, the presence of a large amount of water is able to modify the climate of the nearby land areas, making them warmer in winter and cooler in summer. Land and sea breezes also take place because of this great moderating property of water.(iii) Pure water is tasteless. The taste in water is due to the gases and solids dissolved in it i.e., impurities present in it. As boiled and distilled water are pure containing no impurities hence they taste flat i.e., are tasteless.

Question 18

Question 6(a)Give a balanced chemical equation for the following:(i) Laboratory preparation of hydrogen.(ii) Preparation of hydrogen from an alkali.

Accepted Answer

(i) Laboratory preparation of hydrogenZn + 2HCl ⟶ ZnCl2 + H2 ↑(ii) Hydrogen from alkaliZn+2NaOH⟶Na2ZnO2[sodium zincate]+H2[g]	ext{Zn} + 2	ext{NaOH} \longrightarrow \underset{	ext{[sodium zincate]}}{	ext{Na}_2	ext{ZnO}_2} + 	ext{H}_2 	ext{[g]}Zn+2NaOH⟶[sodium zincate]Na2​ZnO2​​+H2​[g]

Question 19

Question 6(b)Draw the solubility curve for KNO3 and CaSO4.

Accepted Answer

The solubility curves for KNO3 and CaSO4 are shown below:

Question 20

Question 6(c)Name any two impurities present in the hydrogen gas prepared in the laboratory. Also name the chemical used to remove any one impurity that you have stated.

Accepted Answer

Two impurities present in the hydrogen gas prepared in the laboratory are :Hydrogen sulphide (H2S)Sulphur dioxide (SO2)Lead nitrate solution is used to remove hydrogen sulphide.

Model Question Paper — 2

Section A

Section B