Board Paper of Class 10 2013 Chemistry - Solutions
Answer to this paper must be written on the paper provided separately.
You will not be allowed to write during the first 15 minutes.
This time is to be spent in reading the question paper.
The time given at the head of paper is the time allotted for writing the answers.
Section I is compulsory. Attempt any four questions from Section II.
The intended marks of questions or parts of questions are given in brackets [ ].
- Question 1
(a)From the list given below, select the word(s) required to correctly complete blanks (i) to (v) in the following passages. The words from the list are to be used only once. Write the answers as (a) (i), (ii), (iii) and so on. Do not copy the passage.
[ammonia, ammonium, carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt, water]
 i. A solution M turns blue litmus red, so it must contain (i) ________ ions; another solution O turns red litmus blue and hence must contain (ii)_____ ions. ii. When solution M and O are mixed together, the products will be (iii) _____and (iv) _________. iii. If a piece of magnesium was put into a solution M, (v)______ gas would be evolved. (b)Identify the gas evolved in the following reactions when  i. Sodium propionate is heated with soda lime. ii. Potassium sulphite is treated with dilute hydrochloric acid. iii. Sulphur is treated with concentrated nitric acid. iv. A few crystals of KNO3 are heated in a hard glass test tube. v. Concentrated hydrochloric acid is made to react with manganese dioxide. (c)State one appropriate observation for each of the following:  i. Concentrated sulphuric acid is added drop wise to a crystal of hydrated copper sulphate. ii. Copper sulphide is treated with dilute hydrochloric acid. iii. Excess of chlorine gas is reacted with ammonia gas. iv. A few drops of dilute hydrochloric acid are added to silver nitrate solution, followed by the addition of ammonium hydroxide solution. v. Electricity is passed through molten lead bromide. (d)Give suitable chemical terms for the following:  i. A bond formed by a shared pair of electrons with both electrons coming from the same atom. ii. A salt formed by incomplete neutralisation of an acid by a base. iii. A reaction in which hydrogen of an alkane is replaced by a halogen. iv. A definite number of water molecules bound to some salts. v. The process in which a substance absorbs moisture from the atmospheric air to become moist and ultimately dissolves in the absorbed water. (e)Give a chemical test to distinguish between the following pairs of compounds:  i. Sodium chloride solution and sodium nitrate solution ii. Hydrogen chloride gas and hydrogen sulphide gas iii. Ethene gas and ethane gas iv. Calcium nitrate solution and zinc nitrate solution v. Carbon dioxide gas and sulphur dioxide gas (f) Choose the most appropriate answer from the following options: i.Among the period 2 elements, the element which has high electron affinity is
 ii. Among the following compounds, identify the compound which has all three bonds (ionic, covalent and coordinate bond).
B. Ammonium chloride
C. Sodium hydroxide
D. Calcium chloride
iii. Identify the statement which is incorrect about alkanes:
A. They are hydrocarbons.
B. There is a single covalent bond between carbon and hydrogen.
C. They can undergo both substitution as well as addition reactions.
D. On complete combustion, they produce dioxide and water.
iv. Which of these will act as a non-electrolyte?
A. Liquid carbon tetrachloride
B. Acetic acid
C. Sodium hydroxide aqueous solution acid
D. Potassium chloride aqueous solution
v. Which one of the following will not produce an acid when made to react with water?
A. Carbon monoxide
B. Carbon dioxide
C. Nitrogen dioxide
D. Sulphur trioxide
vi. Identify the metallic oxide which is amphoteric in nature:
A. Calcium oxide
B. Barium oxide
C. Zinc oxide
D. Copper (II) oxide
vii. In the given equation, identify the role played by concentrated sulphuric acid:
S + 2H2SO4 → 3SO2 + 2H2O
A. Non-volatile acid
B. Oxidising agent
C. Dehydrating agent
D. None of the above
viii. Nitrogen gas can be obtained by heating:
A. Ammonium nitrate
B. Ammonium nitrite
C. Magnesium nitride
D. None of the above
ix. Which of the following is not a typical property of an ionic compound?
A. High melting point.
B. Conducts electricity in the molten and in the aqueous solution state.
C. They are insoluble in water.
D. They exist as oppositely charged ions even in the solid state.
x. The metals zinc and tin are present in the alloy:
(g)Solve the following:  i. What volume of oxygen is required to burn completely 90 dm3 of butane under similar conditions of temperature and pressure? ii. The vapour density of a gas is 8. What would be the volume occupied by 24 g of the gas at STP? iii. A vessel contains 'X' number of molecules of hydrogen gas at a certain temperature and pressure. How many molecules of nitrogen gas would be present in the same vessel under the same conditions of temperature and pressure?
- Question 2
a) Group number IA
2nd period Li D O J Ne A Mg E Si H M R T I Q u y
• In this table, H does not represent hydrogen.
• Some elements are given in their own symbol and position in the periodic table, while others are shown with a letter.
With reference to the table, answer the following questions:
 i. Identify the most electronegative element. ii. Identify the most reactive element of group 1. iii. Identify the element from period 3 with least atomic size. iv. How many valence electrons are present in Q? v. Which element from group 2 would have the least ionisation energy? vi. Identify the noble gas of the fourth period. vii. In the compound between A and H, what type of bond would be formed and give the molecular formula for the same. b)Compare the compounds carbon tetrachloride and sodium chloride with regard to solubility in water and electrical conductivity.
- Question 3
a)Choosing the substances from the list given below, write balanced chemical equations for the reactions which would be used in the laboratory to obtain the following salts: Dilute sulphuric acid Copper Copper (II) carbonate Iron Sodium carbonate Sodium Sodium chloride Zinc nitrate  i. Sodium sulphate ii. Zinc carbonate iii. Copper (II) sulphate iv. Iron (II) sulphate b)State two relevant observations for each of the following: i. Ammonium hydroxide solution is added to copper (II) nitrate solution in small quantities and then in excess. ii. Ammonium hydroxide solution is added to zinc nitrate solution in minimum quantities and then in excess. iii. Lead nitrate crystals are heated in a hard glass test tube.
- Question 4
a)Copper sulphate solution is electrolysed using copper electrodes.
Study the diagram given below and answer the question which follows:
 i. Which electrode to your left or right is known as the oxidising electrode and why? ii. Write the equation representing the reaction which occurs. iii. State two appropriate observations for the above electrolysis reaction. b)Using the information above, complete the following:
X Y Normal Electronic Configuration 2, 8, 7 2, 8, 2 Nature of oxide Dissolves in water and turns blue litmus red Very low solubility in water. Dissolves in hydrochloric acid Tendency for oxidising and reducing reactions Tends to oxidize elements and compounds Tends to act as a reducing agent Electrical and Thermal conductivity Very poor electrical conductor Poor thermal conductivity Good Electrical Conductor Good thermal conductor Tendency to form alloys and amalgams No tendency to form alloys Form alloys i. __________ is the metallic element. ii. Metal atoms tend to have a maximum of __________ electrons in the outermost energy level. iii. Non-metallic elements tend to form ______ oxides, while metals tend to form ______oxides. iv. Non-metallic elements tend to be ______ conductors of heat and electricity. v. Metals tend to ____electrons and act as ___ agents in their reactions with elements and compounds.
- Question 5
a)Give balanced equations for each of the following:  i. Reduction of hot copper (II) oxide to copper using ammonia gas. ii. Oxidation of carbon with concentrated nitric acid. iii. Dehydration of sugar crystals using concentrated sulphuric acid. b)Copy and complete the following table in relation to an important industrial process:
Name of the process Temperature Catalyst Equation for the catalyzed reaction Haber's process c)The following questions relate to the extraction of aluminium by electrolysis: i. Name the other aluminium-containing compound added to alumina and state its significance. ii. Give the equation for the reaction which takes place at the cathode. iii. Explain why it is necessary to renew the anode periodically.
- Question 6
a)Give balanced equations for the laboratory preparations of the following organic compounds:  i. A saturated hydrocarbon from iodomethane. ii. An unsaturated hydrocarbon from an alcohol. iii. An unsaturated hydrocarbon from calcium carbide. iv. An alcohol from ethyl bromide. b)Give the structural formulae for the following: i. An isomer of n-butane. ii. 2-propanol iii. Diethyl ether c)Give reasons for the following: i. Methane does not undergo addition reactions, but ethene does. ii. Ethyne is more reactive than ethane. iii. Hydrocarbons are excellent fuels.
- Question 7
a)O2 is evolved by heating KClO3 using MnO2 as a catalyst.
 i. Calculate the mass of KClO3 required to produce 6.72 litre of O2 at STP.
[atomic masses of K = 39, Cl = 35.5, O = 16]
ii. Calculate the number of moles of oxygen present in the above volume and also the number of molecules. iii. Calculate the volume occupied by 0.01 mole of CO2 at STP. b)Identify the following substances which are underlined:  i. An alkaline gas which produces dense white fumes when reacted with hydrogen chloride gas. ii. An acid which is present in vinegar. iii. A gas which does not conduct electricity in the liquid state but conducts electricity when dissolved in water. iv. A dilute mineral acid which forms a white precipitate when treated with barium chloride solution. v. The element which has the highest ionisation potential.