In this article I am providing solutions to all the questions of both objective and long answer type questions of ICSE 2012 Board's Chemistry paper for the benefit of ICSE students. Students can download ICSE Board's paper from this link of ISC in pdf format: Chemistry(Science Paper-2)2012 Icse Board's Paper
(Note: If chemical elements and compounds names are there in the answer, unless or otherwise they mention to write them in symbols or formula there is no need to write them. If you like them to write in symbols or formula you must sure to write them correctly otherwise if any mistake come you loose your marks.)
(a) Name the following
(iii) Sulphur dioxide
(iv) Nitrogen dioxide
(v) Hydrogen sulphide
(b) State one observation for each of the following:
(Note: For answering these questions regarding chemical reactions, colors of the products formed should be mentioned clearly in the answers)
(i) A chalky white precipitate is formed and which doesn't dissolve in excess of ammonium hydroxide.
(ii) Brown color of bromine fades away.
(iii) Blue color of copper sulphate fades and reddish brown layer of copper appears.
(iv) Reddish brown gas is evolved and a precipitate is formed. The precipitate is yellow in color when hot but turns white in cold condition.
(v) A rust brown precipitate is formed and is insoluble in excess ferric chloride solution.
(c) Some word/words are missing in the following statements. You are required to rewrite the statement in the correct form using the appropriate word/words:
(i) Ethyl alcohol is dehydrated by concentratedsulphuric acid at a room temperature about 170 Celsius degrees.
(ii) Aqua regia contains 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 towards cathode during electrolysis.
(v) Magnesium reacts with very dilute nitric acid to liberate
(Note: For these questions to write correctly, not only you have to read the chemical reactions thoroughly but you have to know in which conditions i.e. low temperature, high temperature, specific temperature, in the presence of dilute or conc. acid, high or low pressure etc. these reactions occur.)
(d) Choose the correct answer from the options options given below:
(i) (D) Argon
(ii) (B) Calcium
(iii) (D) 22
(iv) (D) Aqueous Acetic acid
(v) (A) Magnesium oxide
(Note: Choose only one correct option from the answer, write the alphabet as well as answer to make the answer clear)
(e) Match the following:
(1) Acid salt------> (C) Sodium hydrogen sulphate
(2) Double salt----> (A) Ferrous ammonium sulphate
(3) Ammonium hydroxide solution------> (E) contains ions and molecules
(4) Dilute hydrochloric acid------->(B) contains only ions
(5) Carbon tetrachloride---------> (D) contains only molecules
(Note: In ICSE system, you have to write terms of first column of words as it is and then you have to provide answers directly as shown above.)
(f) Give the structural formula of the following:
(i) Methanoic acid (ii) Ethanol (iii) Ethyne (iv) Acetone (v) 2-Methyl isopropane
Refer structural formula diagrams from the text.
(g) Concentrated nitric acid oxidizes phosphorus to phosphoric acid according to the following equation:
P + 5HNO3 (Conc.)---------->H3PO4 + H2O + 5NO2
If 9.3 g. phosphorus was used in the reaction , calculate:
(i) Number of moles of phosphorus taken
31 g. of phosphorus = 1 mole of it.
9.3 g. of phosphorus = 1/31 x 9.3 = 0.3 moles
(ii) The mass of phosphoric acid formed
Molecular weight of H3PO4 (H=1, P=31, O=16)= (1x3 + 1x31 + 4x16 =98g.)
9.3g. of phosphorus produces = 98/31x 9.3 = 29.4g.
(iii) The volume of nitrogen dioxide produced at STP
31g. of phosphorus produces = 5 x 22.4 liters of NO2
9.3g. of phosphorus produces = 5x22.4/31 = 33.6 liters
(h) Give reasons for the following:
(i) Iron rendered passive with fuming nitric acid.
Iron forms a coating of its oxide and nitrate stops further reaction.
(ii) An aqueous solution of sodium chloride conducts electricity
Aqueous solution contains free mobile ions to conduct electricity.
(iii) Ionization potential of the element increases across a period.
As Ionization potential increase across a period, atomic size decreases and nuclear charge increases. It makes removal of electron becomes difficult and more energy is required to remove electron. Hence Ionization potential value increases.
(iv) Alkali metals are good reducing agents.
Alkali metals have greater tendency to loose electrons and hence they are good reducing agents.
(v) Hydrogen chloride gas cannot be dried over quick lime.
Hydrogen chloride gas is acidic in nature while quick lime is basic in nature and hence they react.
Section II (40 Marks)
(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 reaction (i) to (v). Some role/s may be repeated.
(A) Dilute acid (B) Dehydrating agent (C) Non-volatile acid (d) Oxidizing agent.
(i) Dehydrating agent
(Explanation: Conc.H2SO4 removes water from hydrated copper sulphate to form CuSO4)
(ii) Oxidizing agent
(Explanation: Conc.H2SO4 oxidizes Sulphur to SO2.)
(iii) Non-volatile acid
(iv) Dilute acid
(Explanation: MgO reacts only with dilute acid.
(v) Oxidizing agent
(Explanation: Addition of oxygen to Zn S from H2SO4 occurs and so it acts as a oxidizing agent)
(b) Give balanced equations for the following reactions:
(i) Dilute nitric acid and Copper carbonate
CUCO3 + 2HNO3---------> CU(NO3)2 + H2O + CO2
(ii) Concentrated hydrochloric acid and Potassium permanganate solution
2KMnO4 + 16 HCl----------> 2KCl + 2 MnCl 2 +8H20 +5Cl2
(iii) Ammonia and oxygen in the presence of a catalyst
4NH3 + 5O2 ---------> 4NO + 6H2O (Mention Pt above and 800 Celsius degree below the arrow)
(iv) Silver nitrate solution and sodium chloride solution
AgNO3 + NaCl--------> AgCl(Ppt.)+ NaNO3
(v) Zinc sulphide and dilute sulphuric acid
ZnS + H2SO4--------> ZnSO4 + H2S
(Note: After writing the equation for the reaction, see that both side of the reaction are balanced, otherwise you loose marks)
(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 electrolysis (Fe+2,Cu+2,Pb+2,H+)
(ii) The metallic electrode which doesn't take part in an electrolytic reaction (Cu,Ag,Pt,Ni)
(iii) The ion which is discharged at the anode during the electrolysis of copper sulphate solution using copper electrodes as anode and cathode(Cu+2,OH-,SO4,H+)
(iv) When dilute sodium chloride electrolyzed using graphite electrodes, the cation discharged at the cathode most readily(Na+,OH-,H+,Cl-)
(v) During silver plating of an article using potassium argentocyanide as an electrolyte, the anode material should be(Cu,Ag,Pt,Fe)
(b) Match the properties and uses of alloys in List 1 with appropriate answer with List2.
(i) The alloy contains Cu and Zn, is hard, silvery and it is used in decorative articles---------> B. Brass
(ii) It is stronger than Aluminium, light and is used in making light tools----------> A. Duraluminin
(iii) It is lustrous, hard, corrosion resistant and used in surgical instruments---------->D. Stainless steel
(iv) Tin lowers melting point of the alloy and is used for soldering purpose-----------> E. Solder
(v) The alloy is hard, brittle, takes up polish and is used for making statues------------>C. Bronze
(Note: For matching you have to write List 1 items as it is and you have to join correct answers from List 2 items by writing. Don't use numbering system or any method which makes it difficult and confusion to the examiner in evaluating your answer.)
(a) Identify the anion present in the following compounds:
(i) Compound X on heating with copper turnings and 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 ammonium hydroxide.
(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has no effect on acidfied potassium dichromate solution
(iv) Compound L on reacting with barium chloride solution gives a white precipitate 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
When dilute sulphuric acid is added to Sodium carbonate, a odorless, colorless gas is evolved. This gas turns lime water milky indicate the evolved gas is CO2. Potassium dichromate paper doesn't show any change with this gas.
When dilute H2SO4 is added to sodium sulphate, a suffocating gas is evolved which turn potassium dichromate paper green.
(ii) Ferrous nitrate and Lead nitrate
If NaOH solution is added to ferrous nitrate, a dirty green precipitate is formed which is insoluble in excess of NaOH.
If NaOH solution is added to Lead nitrate, it forms a chalky white precipitate which is soluble in excess NaOH solution.
(iii) Manganese dioxide and Copper (II) oxide
If conc.HCl is added to MnO2, a greenish yellow colored chlorine gas is formed. The solution is brownish.
If conc.HCl is added to Copper(II) oxide, no gas is evolved. The solution is bluish.
(c) Draw an electron dot diagram to show the structure of hydronium ion. State the type of bonding present in it.
For dot diagram refer text book.
(a) 67.2 liters of hydrogen combines with 44.8 liters of nitrogen to form ammonia under specific conditions as:
N2(g) + 3H2(g) --------> 2NH3(g)
Calculate the volume of ammonia produced. What is the other substance, if any, that remains in the resultant mixture?
Ans. 3 Volume of hydrogen produces 2 volumes of ammonia
67.2 liters of hydrogen produces how much ammonia?
= 2/3 x 67.2 =44.8 liters
3 Volumes of hydrogen reacts with 1 volume of nitrogen
67.2 liters of hydrogen reacts with how much of nitrogen?
= 1/3 x 67.2 = 22.4 liters
Nitrogen left = 44.8 - 22.4 = 22.4 liters
(ii) The mass of 5.6 dm3 of a certain gas at STP is 12.0g. Calculate the relative molecular mass of the gas.
Ans. 5.6 dm3 of gas weighs 12g
22.4 dm3 of gas weighs = 12/5.6 x 22.4 = 44.8 g
(iii) Find the total percentage of Magnesium in magnesium nitrate crystals, Mg(NO3)2.6H2O (Mg=24,N=14,O=16,H-=1)
Molecular mass of Mg(NO3)2.6H2O = 24 + (14+48)+6(18) = 256
Percentage of magnesium = 24/256x100 = 9.375%
(b) Ans. A. NaCl + H2SO4---------> NaHSO4 + HCl (Mention below 200 Celsius degrees above the arrow)
B. Fe + 2HCl--------> FeCl2 + H2
C. HCl(g) +NH3(g)-------> NH4Cl(s)
D. PbO2 + 4HCl--------> PbCl2 +2H2O + Cl 2
(a) Name the following metals:
(i) A metal present in cryolite other than sodium
(ii) A metal which is unaffected by dilute or concentrated acid
(iii) A metal present in period 3, group 1, of the periodic table.
(b) The following questions are relevant to the extraction of Aluminium:
(i) State the reason for the addition of caustic alkali to bauxite ore during purification of bauxite.
Ans. Bauxite dissolves in caustic alkali and thus impurities can be separated.
(ii) Give a balanced chemical reaction for the above reaction.
Ans. Al2 O3.2H2O + 2NaOH ------------> 2NaAlO2 +3H2O
(iii) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and one reason for the addition.
Ans. Fluorspar. This substance act as a solvent and it increasers conductivity.
(c) The following questions are based on the preparation of ammonia gas in the laboratory:
(i) Why ammonium nitrate is not used in the preparation of ammonia gas in the laboratory
Ammonium nitrate is an explosive substance and on heating it decomposes into nitrous oxide and water vapor.
(ii) Name the compound used as a drying agent during the process.
(iii) How ammonia gas is collected?
Ans. Ammonia gas is collected by downward displacement of air.
(iv) Explain why it is not collected over water?
Ans. Ammonia is highly soluble in water and so we cannot collect ammonia over water.
(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
Ans. Acetic acid
(iii) A hydrocarbon which on catalytic hydrogenation gives a saturated hydrocarbon
(iv) An organic compound which is used as thermometric liquid
(b)(i) Why is pure acetic acid is known as glacial acetic acid?
Ans. Pure anhydrous acetic acid on cooling form a crystalline icy mass. Its melting point is 17 Celsius degrees. Hence pure acetic acid is known as glacial acetic acid.
(ii) Give chemical equation for the reaction between ethyl alcohol and acetic acid.
Ans. C2H5OH + CH3COOH --------> CH3COOC2H5 + H2O (Mention conc.H2SO4 above the arrow)
(c) There are three elements E,F,G with atomic number 19,8,17 respectively.
(i) Classify the elements as metals and non-metals
Ans. E------> 19------> 2,8,8,1----->Metal
(ii) Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound.
Ans. Chemical formula: EG
Type of chemical bond: Ionic bond.
|Guest Author: I A Khan 25 Feb 2014|
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