S.S.L.C.
EXAMINATION, SEPTEMBER 2020
SUBJECT:
SCIENCE ( CHEMISTRY )
2. Identify
the correct electron dot structure of nitrogen molecule in the following :
(A) (B)
(C) (D)
4. The
atomic numbers of elements A, B, C and D are 3, 9, 4 and 8 respectively.
Elements having metallic nature among these are (A) B and D (B) A and B
(C) A and C (D) B and C.
Ans. :
(C) A and C
8. The name
and the molecular formula of the unsaturated hydrocarbon having general formula
Cn H n 2 and containing 3 carbon atoms is
(A) propane, C3H8 (B) Cyclopropane, C3H6 (C) Propyne, C3H4 (D) Propene, C3H6.
Ans. : (D)
Propene, C3H6.
10. What
are amphoteric oxides ?
Ans. : Metallic oxides that show both acidic and
basic behaviour are called amphoteric oxides.
12. Can
detergent be used to test hardness of water ? Give reason.
Ans. : Detergents give foam / lather with both hard
water and soft water and do not form scum
15.
Manufacturers of chips, flush the packets of chips with nitrogen gas. Why ?
Ans. : To prevent the chips from getting oxidised.
OR To prevent rancidity.
18. Draw
the diagram of the arrangement of apparatus to show that acid solution in water
conducts electricity and label the battery.
OR
Draw the diagram of the arrangement of apparatus showing the reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning and label the zinc granules.
22. How are
the limitations of Mendeleev’s periodic table rectified in the modern periodic
table ? OR How does the atomic size vary in groups and periods of the modern
periodic table ? Why ?
Ans. : 1. In Mendeleev’s periodic table, since the
elements were arranged based on increasing order of atomic mass, the sequence
was inverted so that the elements with the similar properties could be grouped
together ( For example, Cobalt appeared before Nickel ) Isotopes did not have
any places.
2. Limitations of Mendeleev periodic table were
rectified in the modern periodic table by arranging the elements in the
increasing order of atomic number and also electronic configuration.
3. The problem of isotopes was solved. ( Full mark can be credited if only the
second and third points are written ) OR Atomic size increases down
the group.
4. Because new shells are being added as we go
down the group, this increases the distance between the outermost electrons and
the nucleus.
5. The
atomic size decreases on moving from left to right along a period.
6. Because an increase in nuclear charge tends to
pull the electrons closer to the nucleus.
24. Draw
the diagram of the apparatus used in refining of copper from copper sulphate
solution. Label the following parts :
i) Cathode
ii) Anode mud.
26. Strips of
zinc, iron, magnesium and copper are taken in the test tubes A, B, C and D
respectively. Same quantity of ferrous sulphate solution is added to these test
tubes. In which test tubes chemical reaction will occur ? Why ? Write the
chemical equations for the reactions taking place here.
Ans. : Chemical reaction occurs in test tubes A and
C.
1. Because zinc and magnesium are more reactive
than iron. OR
Zinc and magnesium are found above iron in the
reactivity series of metals.
2. Zinc + Ferrous sulphate → Zinc sulphate + Iron
OR Zn + FeSO4 → ZnSO4+ Fe 2 1
3. Magnesium + Ferrous sulphate → Magnesium
sulphate + Iron OR Mg + FeSO4 → MgSO4+
Fe
29. Write
the balanced chemical equations for the following chemical reactions. How can
we confirm by observation that these chemical reactions are taking place ?
a) Lead
nitrate is heated.
b) Sodium
sulphate reacts with Barium chloride.
Ans. :
a) 2Pb ( NO3)2 → 2PbO + 4NO2 +
O2 1
By the formation of brown coloured fumes.
b) Na2SO4+ BaCl2 → BaSO4+ 2NaCl 1 By the formation of white coloured precipitate.
32. Write
the molecular formulae and two uses of each of the following compounds :
a)
Bleaching powder
b) Plaster
of Paris. OR What is a strong acid ? Explain how tooth decay is caused. How can
it be prevented ?
Ans. : a) CaOCl2
Uses
1. for bleaching cotton and linen in the
textile industry, for bleaching wood pulp in paper factories and for bleaching
washed clothes in laundry.
2. as an oxidising agent in many chemical
industries
3. to make
drinking water free from germs.
b) CaSO4. 2
1 H2O 2 1
Uses
1. for making toys
2. making materials for decoration
3. for making surfaces smooth.
34. a) What
are structural isomers ? Write two structures of butane molecule.
b) How
would you distinguish experimentally between an alcohol and a carboxylic acid ?
Ans. : a) Carbon compounds with identical molecular
formula but different structures are called structural isomers.
b) Carboxylic acid reacts with carbonates and
hydrogen carbonates to give rise to a salt, carbon dioxide and water. Alcohol will not react with carbonates and
hydrogen carbonates.
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