UME 1982 CHEMISTRY ANSWERS
1. Volume
of H = 20cm3
Total
volume of the mixture = (20 +35 + 15 + 10) = 80cm3
Volume fraction of H =
= 0.25
Since mole is
volume
: mole fraction = 0.25 [D]
2.
|
|
C
|
H
|
|
% composition
|
85.71%
|
14.29%
|
|
|
=7.14
|
14.29
|
|
Mole Ratio
|
= 1
|
= 2
|
Empirical formula = CH2
56cm3 of CH2 = 0.07g
22400cm3 of CH2
=
×
= 28g
(CH2)n = 28
14n = 28
n =
= 2.
Hence, molecular formula = (CH2)2
= C2H4 [C]
3. P1
= 750mmHg, V1 = 100cm3
T1 = 308K, P2
= 1000mmHg,
T2 = 308K V2
= ?
=
=
=
75cm3
[C]
4. At
boiling point, water changes into vapour due to increase in the average kinetic
energy of the molecules. As the kinetic energy of the molecules increases, they
collide more frequently with each other and with the continuity leading to increase
in pressure [E].
5. The
type of bond between (NH3) in ammonia molecule is covalent bond.
Ammonium ion (NH4+) formed when H combines with ammonium via
co-ordinate bond. The bond between ammonium ion and chlorine in ammonium
chloride (NH4Cl) is ionic bond [C]
6. Contribution
of
=
×
=
5g
Contribution of
=
×
=
16.5
Relative atomic mass = (5 +16.5) = 21.5g [C]
7. Neutralization
reaction is a reaction between acid and base to form salt and water
HNO3 + NaOH
NaNO3 + H2O [D]
8. Electrolytic
equation of Cu: Cu2+ + 2e
Cu
1 mole of Cu requires 2F =193,000C
Quantity of electricity passed = 10 x 3600 =
3600
Number of mole =
×
= 0.186
mole
Since
copper was used as electrodes, 0.186 mole of copper anode dissolves and gets
deposited at the cathode. The original concentration of Cu2+ remains
unchanged because only the dissolved copper from the anode gets deposited at
the cathode [B]
|
C O
O H
|
|
C O
O H
|
|
CO2 + CO
|
|
- H2O
|
|
Conc.
H2SO4
|
9.
From the above equation,
conc. sulphuric acid removes a molecule of water from ethanedioic acid [C]
10. Cu +
2H2SO4
CuSO4 + 2H2O + SO2
From the above equation:
Cu being lower than H in the
electrochemical series cannot displace it, instead concentrated sulphuric acid
attacks copper to liberate sulphur (IV) oxide [B]
11.
12. Equation
for the reaction:
C3H4 + 2Br2
C3H4Br4
From the above equation 320g of bromine reacted with 40g
of propyne 8g of bromine will react with
×
=
1g [B]
13. In a
redox reaction, there is both oxidation and reduction. Decomposition of Ca(HCO3)2
does not involve oxidation and reduction [C].
14. Molarity
of NaOH = 0.2
Volume of NaOH =
= 0.5dm3
No of mole (n) = MV
n = 0.2 x 0.5 = 0.1
Molar mass of NaOH = 40g
Mass of NaOH = 0.1 x 40 = 4g [D]
15. Factors
that increase the rate of chemical rxn include: increase in temperature,
concentration, pressure and surface area as well as the presence of a catalyst
and light [C]
16. From
the equation, increase in the amount of ammonia means favouring the forward
reaction since the reaction is exothermic (-∆H). Decrease in temperature will
favour the forward reaction [C]
17. Heat
of combustion = mcθ = 100 x 4.2 x 40 = 16800J. Heat of combustion of 0.16g of
methane = 16800J. Heat of combustion of 1 mole of methane =
×
=
=
1680KJ [E]
18. A
base does not react with a neutral solution. Sodium trioxocarbonate is a base
and thus cannot react with water which is neutral [B]
19. Brass
is an alloy formed by adding zinc to a copper based metal to form a better
quality material that is stronger, more malleable and more resistant to
corrosion [A]
20. Molarity
of KOH = 1
Volume of KOH =
=
0.25dm3
No of mole = MV = 1 x 0.25 = 0.25mole
Molar mass of KOH = (39 + 17) = 56g
Mass of KOH = (0.25 x 56) = 14g [E].
21. Equation
for the reaction:
2H2 + O2
2H2
M.R .2 : 1 : 2
V.R 40 : 20 :
40
Volume of unreacted H2 = (60 – 40) = 20cm3
Volume of steam formed = 40cm3
Volume of residual gas = vol of steam formed + volume of
unreacted H2 = (40 + 20) = 60cm3 [A]
22. Equation
for the reaction:
CaO + CaCO3
2CaO +CO2
From the equation, the CO2 was produced by
CaCO3.
44g of CO2 was produced by 100g of CaCO3
0.33g of CO2 will be produced by
=
0.75g
Mass of the mixture = 1g
Mass of CaO in the mixture = (1 - 0.75)
% of CaO =
=
25% [C]
23. Molecular
mass of O = 32g
Methane having a lower molecular mass will diffuse faster
than oxygen
Using Graham’s law of diffusion
=
=
=
=
1.4
The rate of diffusion of methane is 1.4 [C].
24. According
to Charles Law, at constant pressure, the volume of a given mass of a gas is
directly proportional to the temperature
[C]
25. Insoluble chlorides like
silver chloride is prepared by double decomposition of silver nitrate and brine
to produce a white precipitate of AgCl which turns black on exposure to air:
AgNO3 + NaCl
AgCl +
NaNO3
[D]
26. No
of valence electrons in x = 6
No of valence electrons in Y = 1
Valency of X = (8 -6) = 2
|
1
|
|
Y
|
|
X
|
|
2
|
|
= Y2X [C]
|
27. Nitrogen
obtained from atmospheric air contains rare gases which cannot be removed due
to their invert nature. This adds to the density of nitrogen making it denser
than that prepared from nitrogen containing compound [D]
28. 5 components
of air include oxygen, nitrogen, carbon(IV)oxide, rare gases and water vapour.
When passed through alkaline pyrogallol, carbon(IV)oxide and Oxygen are
absorbed. When passed through quick lime, water vapour is absorbed. The only
gases left are nitrogen and rare gases [D]
29. Since
the crystals of KClO3 began to form at 66oc, this is the
saturation point. Mass of KClO3 that saturated 40cm3 of water = 9.8g
Mass of KClO3 that will saturate 1dm3
of water =
×
= 245g
Molecular mass of KClO3 = 122.5g
Solubility
=
2mol/dm3 [E]
30. Equation
for the reaction
2H2 + O2
2H2
From the above equation, mole ratio of hydrogen to oxygen
is 2:1.
Since volume
mole,
volume ratio of hydrogen to oxygen = 2:1
Thus, 50cm3 of hydrogen will react with 25cm3
of oxygen
Volume of unreacted oxygen = (100 - 25) = 75cm3
Volume of steam formed = 50cm3
The steam formed was absorbed by the deliquescent CaCl2
Hence, volume of gas left = 75cm3 [D]
31.
An
acid is said to be weak if it is partially or incompletely ionized or
dissociated in water
[E]
32. Cations
present in caustic soda (NaOH) solution = Na+ and H+
Anion present = OH-
During electrolysis, the cations Na+ and H+
migrate towards the cathode where H+ is preferentially discharged due to its
higher concentration and lower position in the electrochemical series than Na.
The sodium ion which is still in solution close to the cathode associates with
OH- causing increased alkalinity at the cathode [E]
33. Amphoteric
oxides are oxides of metals that react with both acid and base to form salts eg.
oxides of (ZALT): zinc, aluminum, lead and tin.
[D]
34. From
the solubility curve:
solubility at 80oC
= 0.4mol/dm3
Solubility at 40oC = 0.3mol/dm3
On cooling from 800C – 40oC,
no of mole of X that crystallized out = (0.4 – 0.3) =
0.1mole
Molecular mass of X = 160g
Mass of X that crystallized out
= 0.1 x 160 =
16g [D]
35. Ethyne
is a colourless and neutral gas that burns with a sooty (smoky) flame and is
prepared by the action of cold water on white solid called calcium carbide: CaC2
+ 2H2O
C2H2
+ Ca(OH)2 [C]
36. Cellulose
is an unbranched polysaccharide which exists in its pure form as cotton wool.
Other cellulose containing compounds are flax, sisal, straw, jute hemp, etc [D]
37. Addition
reaction is undergone by unsaturated organic compounds with double or triple
bonds eg. Alkene and alkyne. The compound C2H4 belongs to
the homologous series – alkene. Thus, it undergoes addition reaction with
hydrogen, halogens and hydrogen halides
[C]
38. Sulphur(IV)oxide
is a reducing agent but it acts as an oxidizing agent in the presence of a more
powerful reducing agent like hydrogen sulphide. It oxidizes hydrogen sulphide
to sulphur [D]
39. Cations
present in NaCl solution are: Na+ and H+
Anions
present = Cl- and OH-. During electrolysis, Na+
and H+ migrate towards the cathode where H+ is
preferentially discharged [C]
40. The phenomenon
whereby a crystalline salt loses its water of crystallization on exposure to a
dry atmosphere is called efflorescence. Examples of efflorescent compounds are
washing soda (Na2CO3.10H2O), Glauber’s salt (Na2SO4.10H2O) [D]
41. Magnesium
and other metals such as aluminum, zinc, iron, lead and copper do not react
with cold water but with steam at red hot.
[B]
42. The
bond between ammonia and hydrogen ion in ammonia ion is called coordinate
(dative) covalent bond whereby the shared electron are donated by ammonia
molecule [B]
43. Ethyl
ethanoate is an ester formed from the reaction of ethanoic acid and ethanol
CH3COOH
+ C2H5OH
CH3COOC2H5
+ H2O [D]
44. Petroleum
is a mixture of hydrocarbons which when separated by fractional distillation
yield its constituent fractions of hydrocarbon such as alkane, alkene
cycloalkanes, aromatic hydrocarbons, etc. hydrogen is not a hydrocarbon [E]
45. In
the equation of chemical equilibrium, the reactants and the products are
gaseous but the mole ratio of the reactants and products are the same. Thus, pressure
will have no effect. [E]
46. In a
chemical equilibrium, some of the ways of increasing the yield of the product
is to supply more of the reactants or remove the products formed. Thus, if D
which is one of the products is continuously removed, more of it will be formed
to keep the system in equilibrium.
[E]
47. Mass
of the metal and oxygen = 1g
Mass of the metal = 0.8
Proportion of the metal in the metallic oxide
=
=
0.0125
Mass of oxygen = (1 – 0.8) = 0.2
Proportion of oxygen =
=
0.0125
Mole Ratio X and O = 0.0125 : 0.0125 = 1 : 1
Formula of the oxide = XO [B]
48. Silver
trioxonitrate undergoes a double decomposition reaction with hydrogen sulphide
to form a black precipitate of silver sulphide
AgNO3 + H2S
Ag2S + 2HNO3 [B]
49. Since
the formation of ammonia is an exothermic reaction (-
H), a decrease in temperature will favour the
reaction. Since the number of mole of the product is less than the number of
mole of the reactant, the reaction involves a decrease in volume and thus will
be favoured by increase in pressure [D]
Due to the presence
of the single bond, the compound belongs to the homologous series- alkane
(ane). The longest carbon chain contains 4 C-atoms (but). The branches are
methyl group at C-2 (2-methyl) and chlorine at C-2 (2-chloro).
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