ICSE Chemistry: 2015

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  • Q1

    (a) Select from the list the gas that matches the description given in each case:

    [ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne]
    (i) This gas is used as a reducing agent in reducing copper oxide to copper.
    (ii) This gas produces dense white fumes with ammonia gas.
    (iii) This gas is used for welding purposes.
    (iv) This gas is also a saturated hydrocarbon.
    (v) This gas has a characteristic rotten egg smell.

    (b) Choose the most appropriate answer for each of the following:

    (i) Among the elements given below, the element with the least electronegativity is:

    1. Lithium
    2. Carbon
    3. Boron
    4. Fluorine

     (ii) Identify the statement which does not describe the property of alkenes:

    1. They are unsaturated hydrocarbons
    2. They decolourise bromine water
    3. They can undergo addition as well as substitution reactions
    4. They undergo combustion with oxygen forming carbon dioxide and water.

     

    (iii) This is not an alloy of copper:

    1. Brass
    2. Bronze
    3. Solder
    4. Duralumin

    (iv) Bonding in this module can be understood to involve coordinate bonding.

    1. Carbon tetrachloride
    2. Hydrogen
    3. Hydrogen chloride
    4. Ammonium chloride

    (v) Which of the following would weigh the least?

    1. 2 gram atoms of Nitrogen.
    2. 1 mole of Silver
    3. 22.4 litres of oxygen gas at 1 atmospheric pressure and 273K
    4. 6.02 X 1023 atoms of carbon

    [Atomic masses: Ag=108, N=14, O=16, C=12]

     

    (c) Complete the following calculations. Show working for complete credit:

    (i) Calculate the mass of Calcium that will contain the same number of atoms as are present in 3.2 g of Sulphur.

    [Atomic masses: S=32, Ca=40]

    (ii) If 6 litres of hydrogen and 4 litres of chlorine are mixed and exploded and if water is added to the gases formed, find the volume of the residual gas.

    (iii) If the empirical formula of a compound is CH and it has a vapour density of 13, find the molecular formula of the compound.

    (d)State one relevant observation for each of the following:

    (i) When crystals of copper nitrate are heated in a test tube.

    (ii) When the gaseous product obtained by dehydration of ethyl alcohol is passed through bromine water.

    (iii) When hydrogen sulphide gas is passed through lead acetate solution.

    (iv) When ammonia gas is burnt in an atmosphere of excess oxygen.

     (v) At the Anode when aqueous copper sulphate solution is electrolysed using copper electrodes.

    (e)Identify the acid which matches the following description (i) to (v):

    (i) The acid which is used in the preparation of a non-volatile acid.

    (ii) The acid which produces sugar charcoal from sugar.
    (iii) The acid which is prepared by catalytic oxidation of ammonia.

    (iv) The acid on mixing with lead nitrate solution produces a white precipitate which is insoluble even on heating.

    (v) The acid on mixing with silver nitrate solution produces a white precipitate which is soluble in excess ammonium hydroxide.

    (f)Give appropriate scientific reasons for the following statements:

    (i)Zinc oxide can be reduced to zinc by using carbon monoxide, but aluminium oxide cannot be reduced by a reducing agent.

    (ii) Carbon tetrachloride does not conduct electricity.

    (iii) During electrolysis of molten lead bromide graphite anode is preferred to other electrodes.

    (iv) The electrical conductivity of acetic acid is less in comparison to the electrical conductivity of dilute sulphuric acid at a given concentration.

    (v) Electrolysis of molten lead bromide is considered to be a redox reaction.

     

    (g) (i) Give balanced chemical equations for the following conversions A, B and C:

    (ii) Differentiate between the terms strong

    electrolyte and weak electrolyte. (stating any two differences)

    (h) Answer the following questions:

    (i) Explain the bonding in methane molecule using electron dot structure.

    (ii)  The metals of Group 2 from top to bottom are

    Be, Mg, Ca, Sr and Ba

    1. Which one of these elements will form ions most readily and why?

    2. State the common feature in the electronic configuration of all these elements.

    Marks:40
    Answer:

    (a)

    i) Ammonia

    ii) Hydrogen chloride

    iii) Ethyne

    iv) Ethane

    v) Hydrogen sulphide

    (b)

    i. (A) Explanation: Electronegativity increases from left to right in a period.

     

    ii. (C) Explanation: They cannot undergo substitution reactions

     

    iii. (C)Explanation: Solder is an alloy of tin and lead.

    iv. (D)

    Explanation: In ammonium chloride, coordinate bond is present between nitrogen and chlorine atom.

    v. (D)

    Explanation:

     

    (c)
    (i)

    (ii)

    (iii)

    (d)

    (i) Reddish brown fumes evolve.

    (ii) The reddish brown colour of bromine water disappears.

    (iii) Black precipitate is obtained.

    (iv) Ammonia burns with a yellowish flame in the atmosphere of excess oxygen. But in presence of catalyst brown vapours are seen

    (v) The size of anode decreases and deposits are seen below the anode.

    (e)

    (i) Nitric acid

    (ii) Conc. sulphuric acid

    (iii) Nitric acid

    (iv) Sulphuric acid

    (v) Hydrochloric acid

    (f)

    (i) Aluminium is a very reactive metal and aluminium oxide is a very stable compound. Therefore, it cannot be reduced by reducing agents such as carbon monoxide. On the other hand, zinc is a moderately reactive metal; therefore, zinc oxide can be reduced by carbon monoxide.

    (ii) Carbon tetrachloride does not conduct electricity because it does not have free ions in the solution. It exists in the form of covalently bonded molecules.

    (iii) Graphite rod is unaffected by the reactive bromine vapours (produced during the reaction).

    (iv) The electrical conductivity depends on number of ions. Acetic acid is a weak acid and it dissociates partially. It produces lesser number of ions as compared to sulphuric acid which is a strong acid and completely dissociates to produce free ions in solution. Therefore, conduction of electric current in acetic is less as compared to dil. H2SO4 at given concentration.

     

    (v) During electrolysis of molten lead bromide, reduction takes place at cathode and oxidation takes place at anode. Therefore, electrolysis of molten lead bromide is a redox reaction.

    (g)

    (i)

    (ii)

    (h)

    (i) Methane molecule is made of carbon and hydrogen. Atomic number of carbon is 6 and its configuration is 2,4. To attain the stable electronic configuration of the nearest noble gas, carbon needs four electrons. Atomic number of hydrogen is 1 and it requires one more electron to become stable. Therefore, in the methane molecule, one atom of carbon shares its four valence electrons, one with each of the four atoms of hydrogen resulting in the formation of four single covalent bond between them.

    (ii)

    (1) Barium (Ba) will form ions most readily because its ionisation potential is lowest in the group.

    (2) All these elements have two electrons in their valence shell.

    View Answer
  • Q2

    (a) Arrange the following as per the instructions given in the brackets:
    (i) Cs, Na, Li, K, Rb (increasing order of metallic character)

    (ii) Mg, Cl, Na, S, Si (decreasing order of atomic size)
    (iii) Na, K, Cl, S, Si (increasing order of ionization energy)
    (iv) Cl, F, Br, I (increasing order of electron affinity)

    (b)Choose the most appropriate answer from the following list of oxides which fit the description. Each answer may be used only once:

    (i) A basic oxide.

    (ii) An oxide which dissolves in water forming an acid.
    (iii) An amphoteric oxide.
    (iv) A covalent oxide of a metalloid.

    (c) Element X is a metal with a valency 2, Y is a non-metal with a valency 3.
    (i)Write an equation to show how Y forms an ion.
    (ii) If Y is a diatomic gas, write an equation for the direct combination of X and Y to form a compound
    .

    Marks:10
    Answer:

    (a)
    (i) Li < Na < K < Rb < Cs
    (ii) Na > Mg > Si > S > Cl
    (iii) K < Na < Si < S < Cl
    (iv) I < Br < F < Cl

    (b)

    i) Na2O

    ii) SO2

    iii) Al2O3

    iv) SiO2
    (c)

     

    View Answer
  • Q3

    (a) Give balanced chemical equations for the following conversions.

    (i)  Ethanoic acid to ethyl ethanoate.
    (ii) Calcium cabide to ethyne.
    (iii) Sodium ethanoate to methane.

     (b) Using their structural formulae identify the functional group by circling them:

                 (i)  Dimethyl ether

             (ii) Propanone

    (c)Name the following:

    (i)  Process by which ethane is obtained from ethene.

    (ii) A hydrocarbon which contributes towards the greenhouse effect.

    (iii) Distinctive reaction that takes place when ethanol is treated with acetic acid.

    (iv) The property of elements by virtue of which atoms of the element can link to each other in the form of a long chain or ring structure.

    (v) Reaction when an alkyl halide is treated with alcoholic potassium hydroxide.

    Marks:10
    Answer:

    (a)

    (b)

    (c)

    (i) Hydrogenation

    (ii) Methane(CH4)

    (iii) Esterification

    (iv) Catenation

    (v) Dehydrohalogenation

    View Answer
  • Q4

    (a) Identify the anion present in each of the following compounds:

    (i) A salt M on treatment with concentrated sulphuric acid produces a gas which fumes in moist air and gives dense fumes with ammonia.

    (ii) A salt D on treatment with dilute sulphuric acid produces a gas which turns lime water milky but has no effect on acidified potassium dichromate solution.

    (iii) When barium chloride solution is added to salt solution E a white precipitate insoluble in dilute hydrochloric acid is obtained.

    (b)The following table shows the tests a student performed on four different aqueous solutions which are X, Y, Z, and W. Based on the observations provided, identify the cation present:


    (c) Give balanced chemical equations for each of the following:

    (i) Lab preparation of ammonia using an ammonium salt.

    (ii) Reaction of ammonia with excess chlorine.

    (iii) Reaction of ammonia with sulphuric acid.

    Marks:10
    Answer:

    (a)

    (i) Chloride ion(Cl)

    (ii) Carbonate ion(CO32–)

    (iii) Sulphate ion (SO42–)

    (b)

    (c)

    View Answer
  • Q5

    (a) Consider the following reaction. Based on the reaction answer the questions that follow:

    Calculate:

    (i)  The quantity in moles of (NH4)2Cr2O7 if 63 g of (NH4)2Cr2O7 is heated.

    (ii)  The quantity in moles of nitrogen formed.

    (iii) The volume in litres or dm3 of N2 evolved at STP.

    (iv) The mass in grams of Cr2O3 formed at the same time. [Atomic masses: H=1, Cr=52, N=14]

    (b) (i) For each of the substance listed below, describe the role played in the extraction of aluminium.

    (1)Cryolite
    (2)Sodium hydroxide
    (3)Graphite
    (ii) Explain why:
    (1)In the electrolysis of alumina using the Hall Heroult’s process the electrolyte is covered with powdered coke.
    (2)Iron sheets are coated with zinc during galvanization

    Marks:10
    Answer:

    (a)


    (b)

    (i)

    (1). Cryolite lowers the fusion temperature from 2050oC to 950oC and enhances the conductivity.

    (2). Sodium hydroxide is used to remove insoluble impurities from the bauxite ore. When bauxite ore is treated with sodium hydroxide, it dissolves aluminum and forms sodium aluminate leaving behind insoluble impurities called red mud (consists of ferric oxide, sand etc.)

    (3). Graphite is used as an electrode in the extraction of aluminium because it has high melting point and is good conductor of electricity.

    (ii)

    (1). In the electrolysis of alumina using the Hall Heroult’s process the electrolyte is covered with powdered coke to reduce the heat loss by radiation and to prevent burning of anode.

    (2). Iron sheets are coated with zinc during galvanization to prevent them from rusting.

    View Answer
  • Q6

    (a)(i) Give balanced chemical equations for the action of sulphuric acid on each of the following:
    (1). Potassium hydrogen carbonate
    (2).Sulphur

     

    (ii) In the contact process for the manufacture of sulphuric acid give the equations for the conversion of sulphur trioxide to sulphuric acid.

    (b)(i) Copy and complete the following table:

    (ii) Write the equation taking place at the anode.

    (c) Explain the following:

    (i) Dilute nitric acid is generally considered a typical acid but not so in its reaction with metals.

    (ii) Concentrated nitric acid appears yellow when it is left standing in a glass bottle.

    (iii) An all glass apparatus is used in the laboratory preparation of nitric acid.

    Marks:10
    Answer:

    (a)

    (b)
    (i)

    (ii)

    (c)

    (i) Nitric acid does not liberate hydrogen on reaction with metals. It is a powerful oxidising agents and it oxidises the hydrogen formed to water.

    (ii) When nitric acid is left standing in a glass bottle, it decomposes to give reddish brown NO2 gas which dissolves in nitric acid to give a yellow colour to nitric acid.

    (iii) Vapours of nitric acid are corrosive and may attack rubber, cork or metal. Therefore, an all glass apparatus is used in laboratory for the preparation of nitric acid.

    View Answer
  • Q7

    (a) The following questions are pertaining to the laboratory preparation of hydrogen chloride gas:

    (i) Write the equation for its preparation mentioning the condition required.

    (ii) Name the drying agent used and justify your choice.

    (iii) State a safety precaution you would take during the preparation of hydrochloric acid.

    (b) An element L consists of molecules.

    (i) What type of bonding is present in the particles that make up L?

    (ii) When L is heated with iron metal, it forms a compound FeL. What chemical term would you use to describe the change undergone by L?

    (c) From the list of the following salts choose the salt that appropriately fits the description given in the following:

    [AgCl, MgCl2, NaHSO4, PbCO3, ZnCO3 KNO3, Ca(NO3)2]

    (i)  A deliquescent salt.

    (ii) An insoluble chloride.

    (iii) On heating this salt gives a yellow residue when hot and white when cold.

    (iv) On heating this salt, a brown coloured gas is evolved.

    Marks:10
    Answer:

    (i)

    (ii) The drying agent used for the preparation of hydrogen chloride gas is conc. sulphuric acid because it does not react with hydrogen chloride gas.

    (iii) During the preparation, the temperature should be maintained near 200oC because above 200oC, sodium sulphate is formed. The sodium sulphate forms a hard crust that sticks to the glass and is difficult to remove. At higher temperature the glass apparatus can crack.

     

    ANS: (b)

    (i) Covalent bonding is observed in similar molecules. Therefore, chemical bonding is present in the particles that make up L.

    (ii) Reduction

     

    ANS: (c)

    (i) MgCl2

    (ii) AgCl

    (iii) KNO3

    (iv) Ca(NO3)2

    View Answer