X - Chemistry 2012 Set 1

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  • Q1

    (a) Some properties of sulphuric acid are listed below. Choose the role played by sulphuric acid as A, B, C or D, which is responsible for the reactions (i) to (v). Some role/s may be repeated.
    (A) Dilute acid
    (B) Dehydrating agent
    (C) Non-volatile acid
    (D) Oxidising agent

    (b) Give balanced equations for the following reactions:
    (i) Dilute nitric acid and copper carbonate.
    (ii) Concentrated hydrochloric acid and potassium permanganate solution.
    (iii) Ammonia and oxygen in the presence of a catalyst.
    (iv) Silver nitrate solution and sodium chloride solution.
    (v) Zinc sulphide and dilute sulphuric acid.

    Marks:10
    Answer:

    (a)

    (i) B, Dehydrating agent
    (ii) D, Oxidising agent
    (iii)
    C, Non-volatile acid
    (iv)
    A, Dilute acid
    (v)
    D, Oxidising agent

    (b)

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  • Q2

    (a) Select the correct answer from the list given in the brackets:
    (i) An aqueous electrolyte consists of the ions mentioned in the list, the ion which could be discharged most readily during the electrolysis [Fe2+,Cu2+,Pb2+,H+].
    (iii) The metallic electrode, which does not take part in an electrolytic reaction [Cu, Ag, Pt, Ni].
    (iv) The ion that is discharged at the cathode during the electrolysis of copper sulphate solutions by using copper electrodes as anode and cathode [Cu2+,OH,SO42–,H+].
    (v) When dilute sodium chloride is electrolysed by using graphite electrodes, the cation is discharged at cathode most readily [Na+,OH,H+,Cl].
    (v) During the silver plating of an article by using potassium argentocyanide as an electrolyte, the anode material should be [Cu,Ag,Pt,Fe].

    (b) Match the properties and the uses of alloys in List 1 with the appropriate answer from List 2.

    List 1

    List 2

    1. The alloy contains Cu and Zn; is hard, silvery and is used in decorative articles.

    A. Duralumin

    2. It is stronger than aluminium; is light and is used in making light tools.

    B. Brass

    3. It is lustrous, hard, corrosion resistant and is used in surgical instruments.

    C. Bronze

    4. Tin lowers the melting point of the alloy and is used for soldering purpose.

    D. Stainless steel

    5. The alloy is hard, brittle, takes up polishing and is used for making statues.

    E. Solder

    Marks:10
    Answer:

    (a)
    (i) Cu2+
    (ii) Pt
    (iii) Cu2+ at cathode
    (iv) H+
    (v) Ag

    (B)
    (i) B
    (ii) A
    (iii) D
    (iv) E
    (v) C

    View Answer
  • Q3

    (a) Identify the anion present in the following compounds:
    (i) Compound X on heating with copper turning and concentrated sulphuric acid liberates a reddish brown gas.
    (ii) When a solution of compound Y is treated with silver nitrate solution, a white precipitate is obtained, which is soluble in excess of ammonium hydroxide solution.
    (iii) Compound Z on reacting with dilute sulphuric acid liberates a gas, which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution.
    (iv) Compound L on reacting with barium chloride solution gives a white precipitate, which is insoluble in dilute hydrochloric acid or dilute nitric acid.

    (b) State one chemical test between each of the following pairs:
    (i) Sodium carbonate and sodium sulphite
    (ii) Ferrous nitrate and lead nitrate
    (iii) Manganese dioxide and Copper (II) oxide.

    (c) Draw an electron dot diagram to show the structure of hydronium ion. State the type of bonding present in it.

    Marks:10
    Answer:

    (a)
    (i) Nitrate (NO3) ion is present.
    (ii) Chloride (Cl) ion is present.
    (iii) Carbonate (CO32–) ion is present.
    (iv) Sulphate (SO42–) ion is present.

    (b)
    (i) Sodium carbonate when treated with dilute HCl will liberate colourless odourless gas (CO2 gas) with strong effervescence. The gas will turn lime water milky and will have no effect on the acidified potassium permanganate solution.
    Sodium sulphite when treated with dilute HCl will liberate colourless gas (SO2 gas) having pungent smell. The gas will decolourise the pink colour of acidified potassium permanganate.

    (ii)Aqueous ferrous nitrate when treated with NaOH solution gives a dirty green precipitate, which remains insoluble in excess of NaOH. The aqueous lead nitrate when treated with NaOH solution gives a chalky white precipitate, which dissolves in excess of NaOH.

    (iii) When manganese dioxide is heated with concentrated HCl, brown colour precipitate is obtained with the evolution of pungent smelling greenish yellow colour chlorine gas. When copper oxide is heated with the concentrate HCl, bluish colour precipitate is obtained and no gas is evolved.

    (c) A water molecule contains two lone pairs of electrons and attracts a hydrogen ion (H+) of the acid (dissolved in water) on an oxygen atom and forms hydronium ion.

    Bonding in hydronium ion: Hydronium ion has two covalent bonds and one coordinate bond between the oxygen and the hydrogen atoms.

    The covalent bonds are formed by the sharing of the electrons of the oxygen atom with the electrons of the hydrogen atoms. The coordinate bond is formed by attaching the proton to the free electron pair of the oxygen atom. The oxygen atom of the water molecule donates a pair of electrons to build the coordinate bond with the proton.

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  • Q4

    (a)

    (i) 67.2 litres of hydrogen combines with 44.8 litres of nitrogen to form ammonia under specific conditions as:

    Calculate the volume of ammonia produced. What is the other substance, if any, that remains in the resultant mixture?

    (ii) The mass of 5.6 dm3 of a certain gas at STP is 12.0 g. Calculate the relative molecular mass of the gas.
    (iii) Find the total percentage of magnesium in magnesium nitrate crystals, Mg(NO
    3)2.6H2O

    [Mg=24, N=14, O=16 and H=1].

    (b) Refer to the flow chart given below and give the balanced equations with the conditions, if any, for the following conversion from A to D.

    Marks:10
    Answer:

    (a)
    (i)

    (ii)

    (iii)

    (b)

    View Answer
  • Q5

    (a) Name the following metals:
    (i) A metal present in cryolite other than the sodium.
    (ii) A metal that is unaffected by dilute or concentrated acids.
    (iii) A metal present in period 3, group 1 of the periodic table.

    (b) The following questions are relevant to the extraction of the aluminum:
    (i) State the reason for the addition of the caustic alkali to bauxite ore during the purification of bauxite.
    (ii) Give a balanced chemical equation for the above reaction.
    (iii) Along with the cryolite and the alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.

    (c) The following questions are based on the preparation of ammonia gas in the laboratory:
    (i) Explain why ammonium nitrate is not used in the preparation of ammonia.
    (ii) Name the compound that is normally used as a drying agent during the process.
    (iii) How is ammonia gas collected?
    (iv) Explain why it is not collected over water.

    Marks:10
    Answer:

    (a)
    (i) Aluminium
    (ii) Platinum
    (iii) Sodium

    (b)

    (i) When finely powdered crude bauxite is heated with a concentrated solution of caustic alkali, the bauxite goes into the solution forming sodium aluminate, while the impurities (mainly Fe2O3 and SiO2) remain insoluble. The undissolved impurities of Fe2O3 and SiO2 are called mud.

    (ii)

    (iii) The name of the substance is fluorspar (CaF2). It reduces the melting point of the mixture and the mixture becomes the good conductor of the electricity.

    (c)
    (i) Ammonium nitrate cannot be used in the preparation of ammonia, as ammonium nitrate is an explosive substance and it dissociates into nitrous oxide and water on heating.
    (ii) Quick lime (CaO) is normally used as a drying agent for drying the ammonia gas.
    (iii) Ammonia gas is collected by the downward displacement of air as it is less dens than air.
    (iv) Ammonia cannot be collected over water because it is highly soluble in water.

    View Answer
  • Q6

    (a) From the following organic compounds given below, choose one compound in each case, which relates to the description [i] to [iv]:
    [ethyne, ethanol, acetic acid, ethene, methane]
    (i) An unsaturated hydrocarbon used for welding purposes.
    (ii) An organic compound whose functional group is carboxyl.
    (iii) A hydrocarbon that on catalytic hydrogenation gives a saturated hydrocarbon.
    (iv) An organic compound used as a thermometric liquid.


    (b)

    (i) Why is pure acetic acid known as glacial acetic acid?
    (ii) Give a chemical equation for the reaction between the ethyl alcohol and the acetic acid.


    (c) There are three elements E, F, G with the atomic numbers 19, 8 and 17, respectively.
    (i) Classify the elements as metals and non–metals.

    (ii) Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound.

    Marks:10
    Answer:

    (a)
    (i) Ethyne
    (ii) Acetic acid
    (iii) Ethene
    (iv) Ethanol

    (b)
    (i) Pure anhydrous acetic acid is also called glacial acetic acid because the anhydrous acetic acid on cooling forms an ice-like mass floating at the surface giving it an appearance of a glacier.

    (ii)

    (c)
    (i) The electronic configuration of element E (Z=19) is 2,8,8,1. The element E belongs to group 1 and is a metal. The electronic configuration of element F (Z=8) is 2, 6. The element F belongs to the second period of group 16 and is a non-metal. The electronic configuration of element G (Z=17) is 2, 8, 7. The element G belongs to group 17 and is a non-metal.
    (ii) The electrovalency of element E (a metal) and element G (a non-metal) is one. Hence, the molecular formula of the compound formed between E and G is EG.

    View Answer
  • Q7

    (a) Name the gas in each of the following:

    (i) The gas evolved on reaction of aluminium with boiling concentrated caustic alkali solution.

    (ii)The gas produced when excess ammonia reacts with chlorine.
    (iii) The gas which turns acidified potassium dichromate clear green.
    (iv) The gas produced when copper reacts with concentrated nitric acid.
    (v) The gas produced on reaction of dilute sulphuric acid with a metallic sulphide.

    (b) State one observation for each of the following:
    (i) Excess ammonium hydroxide solution is added to lead nitrate solution.
    (ii) Bromine vapours are passed into a solution of ethyne in carbon tetrachloride.
    (iii) A zinc granule is added to copper sulphate solution.
    (iv) Zinc nitrate crystals are strongly heated.
    (v) Sodium hydroxide solution is added to ferric chloride solution at first a little and then in excess.

    (c) Some word/words are missing in the following statements. You are required to rewrite the statements in the correct form by using the appropriate word/words:
    (i) Ethyl alcohol is dehydrated by sulphuric acid at a temperature of about 170
    ℃.
    (ii) Aqua regia contains one part by volume of nitric acid and three parts by volume of hydrochloric acid.
    (iii) Magnesium nitride reacts with water to liberate ammonia.
    (iv) Cations migrate during electrolysis.
    (v) Magnesium reacts with nitric acid to liberate the hydrogen gas.

    (d) Choose the correct answer from the options given below:
    (i) An element in period-3 whose electron affinity is zero.
    (A) Neon
    (B) Sulphur
    (C) Sodium
    (D) Argon

    (ii) An alkaline earth metal.
    (A) Potassium
    (B) Calcium
    (C) Lead
    (D) Copper

    (iii) The vapour density of carbon dioxide [C=12, O=16].
    (A) 32
    (B) 16
    (C) 44
    (D) 22

    (iv) Identify the weak electrolyte from the following:
    (A) Sodium chloride solution
    (B) Dilute hydrochloric acid
    (C) Dilute sulphuric acid
    (D) Aqueous acetic acid

    (v) Which of the following metallic oxides cannot be reduced by normal reducing agents?
    (A) Magnesium oxide
    (B) Copper (II) oxide
    (C) Zinc oxide
    (D) Iron (III) oxide


    (e) Match the following:

    (f) Give the structural formula of the following:
    (i) Methanoic acid
    (ii) Ethanal
    (iii) Ethyne
    (iv) Acetone
    (v) 2-Methylpropane

    (g) Concentrated nitric acid oxidises phosphorus to become phosphoric acid, according to the following equation:

    If 9.3 g of phosphorous was used in the reaction, calculate:
    (i) The number of moles of phosphorous taken.
    (ii) The mass of phosphoric acid formed.
    (iii) The volume of nitrogen dioxide produced at STP [H=1,N=14,P=31, O=16].

    (h) Give reasons for the following:

    (i) Iron is rendered passive with fuming nitric acid.

    (ii) An aqueous solution of sodium chloride conducts electricity.
    (iii) Ionisation potential of the element increases across a period.
    (iv) Alkali metals are good reducing agents.
    (v) Hydrogen chloride gas cannot be dried over quick lime.

    Marks:40
    Answer:

    (a)
    (i) Hydrogen gas
    (ii) Nitrogen gas
    (iii) Sulphur dioxide gas
    (iv) Nitrogen dioxide gas
    (v) Hydrogen sulphide gas

    (b)
    (i) On addition of excess ammonium hydroxide solution to lead nitrate solution, a white precipitate of lead hydroxide is formed.
    (ii) Bromine vapours have brown colour. On reaction with ethyne, a colourless solution is obtained and brown colour of bromine vapours disappear.
    (iii) On addition of zinc granule to copper sulphate solution, the blue colour of the copper sulphate solution disappears due to the formation of the colourless zinc sulphate.
    (iv) When zinc nitrate crystals are strongly heated a reddish brown gas is liberated.
    (v) On the addition of sodium hydroxide solution to ferric chloride solution at first a reddish brown precipitate of ferric hydroxide is formed, which remains insoluble in excess of sodium hydroxide.

    (c)
    (i) Ethyl alcohol is dehydrated by concentrated sulphuric acid at a temperature of about 170
    ℃.
    (ii) Aqua regia contains a mixture of one part by volume of concentrated nitric acid and three parts by volume of concentrated hydrochloric acid.

    (iii) Magnesium nitride reacts with warm water to liberate ammonia.

    (iv) Cations migrate to cathode during the process of electrolysis.
    (v) Magnesium reacts with dilute nitric acid to liberate hydrogen gas.

    (d)
    (i) (D)
    (ii) (B)
    (iii) (D)
    (iv) (D)
    (v) (A)

    (e) 1. (C), 2. (A), 3. (E), 4. (B), 5.(D)

    (f)
    (i)

    (ii)

    (iii)

    (iv)

    (v)


    (g)(i)


    (ii)

    (iii)

    (h)
    (i) Fuming nitric acid attacks on iron and forms a thin film of iron oxide on its surface which protects the iron from further attack of air and water (moisture).
    (ii) NaCl is a strong electrolyte. In aqueous solution, it dissociates completely into Na+ and Cl ions. Since, the aqueous solution of NaCl contains free and mobile ions, it conducts electricity.
    (iii) The ionisation potential of the element increases on moving from left to right across a period because the nuclear charge increases across a period.
    (iv) The alkali metals are strong reducing agents as they have low ionisation potential and they can easily donate their valance shell electrons.
    (v) Hydrogen chloride gas cannot be dried over quick lime because quick lime (CaO) is basic in nature and it combines with the moist hydrogen chloride gas to form salt calcium chloride (CaCl2).

    View Answer