UME1985 CHEMISTRY ANSWERS
1.
P-block elements include all the elements in group III to VIII
The elements P, Q and R in the periodic table belongs to group IV,
VI and VII
Thus, they belong to P-block elements [D]
2.
All the elements provided in the options are non metals. However,
graphite which is an allotrope of carbon has a mobile electron in the crystal
lattice because only 3 out of the 4 valence electrons are involved in bond
formation. The presence of this mobile electron in graphite makes them agood
conductor [B]
3.
Element
4.
Weight of CuSO4.XH2O = = 0.499g
Weight of CuSO4 = 0.346g
=
=
0.346 (159.5 + 18x) = 159.5 × 0.499
= 55.2 + 6.2x = 79.6
6.2x = (79.6 – 55.2) = 24.4
X =
= 4 [D]
5.
The criteria for purity are sharp melting point, sharp boiling
point and definite density. A mixture is an impure substance and will not
possess any of the above criteria. Thus, a solid mixture will melt over a range
of temperature eg from 573K to 648K [C]
6.
Molecular mass of O2 = 32g
Molecular mass of H2 = 2g
According to Graham’s law of diffusion, a lighter gas will diffuse
many times faster as the ratio of the square root of their molecular masses.
The ratio of the molecular mass of O2 and H2 =
Square root =
= 4
Hence Hydrogen will diffuse 4 times as fast as oxygen [E]
7.
1 mole of iron (III) oxide = Fe2O3
Molecular mass of Fe2O3 = (2 × 56 ) + (3× 16) 160g
160g of Fe2O3 contains 1 mole.
1kg (1000g) will contain
×
= 6.25mole [C]
8.
In a mixture of K2CO3 and KCl only K2CO3 will react with HCl
Equation for the reaction:
2HCl + K2CO3 2KCl + H2O +
CO2
Applying the volumetric formula:
=
=
=
Molarity of the base K2CO3 = 0.08
Mass of K2CO3 in the mixture = 0.08 × 138 =
11.04g
250cm3 of the mixture contains 3g
1000cm3 of it will contain
×
= 12g
Percentage of K2CO3 =
×
= 92% [E]
9.
G9
10.
From the given graph:
At 353K, the solubility of X = 86g/100g of water and this is
greater than 80g.Thus, 80g of X placed in water will dissolve completely at
that temperature.
At the same temperature of 353K, the solubility of Y is 64g/100g
of water and this is less than 80g. Thus, when 80g of Y is placed in water,
only 64g of it will dissolve leaving behind 16g of Y undissolved ie (80 - 64) =
16g [B]
11.
From the graph,
At 343K, the mass of X that is dissolved = 72g
Molar mass of X = 36g
Solubility of X =
=
= 2.0 mole [D]
12.
Alkalis exhibit the following properties: slippery to touch,
yields alkaline gas with ammonium salts, turns phenolphthalein pink. In
addition, they have a bitter taste (NOT sour taste) and have a PH greater than
7 (NOT less than 7) [D]
13.
According to the general gas equation, temperature increases with
volume and pressure. If each of the volume and pressure are increased by 4
times their original values, temperature will increase by 16 times its original
value ie (16 × 298) = 4768K
Alternatively, using:
=
=
T2 =
= 4768K [E]
14.
Trioxonitrate (V) acid is a very strong oxidizing agent. Unlike
other acids, it does NOT liberate H2 with metals except in a very dilute form
(1%) whereby it reacts with Ca and Mg to liberate H2. This is because any H2
that is initially formed is instantly oxidized to water [B]
15.
The vapour pressure of liquids at a temperature lower than their
boiling points is inversely proportional to their boiling points. This is
because at boiling point, the vapour pressure of a liquid increases to equalize
the atmospheric pressure. Among the given liquids, ethanol has the lowest
boiling point and thus has the highest vapour pressure at that temperature. [C]
16.
Purified nitrogen (I) oxide when passed over heated copper is
reduced to a pure nitrogen gas. Nitrogen prepared from air contains rare gases
as an impurity which adds to the density of the nitrogen [B]
17.
Electrolytic equation of copper:
Cu + 2e- Cu
2e- (2F) of electricity liberated 63.5g of Cu
2F = (2 × 96500) = 193000C
Quantity of electricity passed = (0.193 × 2 × 3600) = 1389.6C
If 193000C liberated 63.5g of Cu ,1389.6C will liberate :
×
= 0.457g [A]
18.
A catalyst has no effect on a chemical equilibrium of a reversible
reaction. It only increases the rate at which equilibrium is attained by
increasing the rate of change in the concentrations of both the reactants and
the products ie X, Y and Z [B]
19.
In chemical combination, the number of positive charges must be
equal to the number of negative charges to form a neutral compound. Gallium
(Ga) with an oxidation state of +3 when combined with sodium (Na) with
oxidation state of of +1 gives a total positive charge of +4. This requires a
negative ion with a total charge of -4 which is provided by 4 moles of OH-.
They combine together to form NaGa(OH)4
[D]
20.
Oxides of nitrogen, carbon monoxide and lead (II) bromide are all
produced from automobile exhaust while methane is produced from decomposition
of plant matter in the absence of air. Combustion of coal produces carbon (IV) oxide
and sulphur (IV) oxide [A]
21.
From the given electrochemical series: K, Na, Ca, Al, Mg, Zn, Fe,
Pb, H, Cu, Hg, Ag, Au. It is wrong to place Al before Mg because Al being
situated at the right of Mg in the periodic table is less electropositive
because electropositivity decreases across the period from left to right. The
correct electrochemical series can be obtained by interchanging Al and Mg [A]
22.
From the equation, enthalpy change is positive . This means that
the reaction is endothermic. Increase in temperature favours the yield of the
products of an endothermic reaction. The formation of the product involves an
increase in volume, thus a decrease in pressure will favour the yield of the
product [A]
23.
In a redox reaction, an oxidizing agent becomes reduced at the end
of the reaction. From the equation, the oxidation state of manganese changed
from +7 in MnO4- to +2 in Mn2+ which means that it was reduced. The overall
reaction represents the oxidation of hydrochloric acid to chlorine using
MnO4- [D]
24.
Factors affecting a chemical system in equilibrium include
temperature, pressure and concentration. Pressure will have effect due to
unequal no of moles of the reactants and products. Adding H will affect the
concentration of the product. Adding argon will have no effect because it is
neither a reactant nor a product of the equation and being a noble gas , it
cannot react. [A]
25.
Only a more electropositive metal can displace a metal from its
solution via a displacement reaction. Among all the elements provided in the
option, only zinc is above iron in the electrochemical series and thus have the
ability to displace it from its solution
[D]
26.
Ethyne is a highly unsaturated hydrocarbon. Partial hydrogenation
produces a more saturated hydrocarbon with double bond called ethane. On
further reaction with hydrogen, the double bond is cleaved to form an
unsaturated hydrocarbon with a single bond called ethane. Equation for the
complete hydrogenation:
C2H2 + 2H2 C2H6 [C]
27.
When chlorine is bubbled through a fleshly prepared solution of
Ca(OH)2, a bleaching powder is formed. Equation for the reaction;
Cl2 + Ca(OH)2
CaOCl2.H2O [B]
28.
Ethanol undergoes partial oxidation with K2CR2O7 to form ethanal
and complete oxidation to form ethanoic acid. This results in the reduction of
the orange coloured oxidizing agent – K2Cr2O7 to green coloured Chromium (III)
ion [E]
29.
The motion of pollen grains suspended in water is a typical
example of Brownian motion which is a random motion of solid particles caused
by the bombardment or collision of the solid particles with the molecules of
the suspending medium [E]
30.
Heat of formation of CO = -110.4KJ/mol
Heat of formation of CO2 = -393KJ/mol
Enthalpy change H = HP – HR = -393.3 – (-110.4)
= -393.3 + 110.4 = -282.9KJ [C]
31.
Esters undergo hydrolysis in acid to form alkanoic acid and
alkanol. The formula shown is propyl ethanoate and its hydrolysis will yield
ethanoic acid CH3COOH and propanolC3H7OH
[C]
32.
Nitrogen (IV) oxide is a mixed acid anhydride. It reacts with
alkalis to form water and a mixture of two salts namely: dioxonitrate (III) and
trioxonitrate (V). Equation for the reaction is shown below:
2NaOH + 2NO2 NaNO3 +
NaNO2 + H2O [A]
33.
Oxidation of secondary alkanol gives ketones (alkanones). The
formula given is butan-2-ol which is a secondary alkanol. Its oxidation gives
butane-2one (C2H5COCH3) [A]
34.
The confirmatory test for tetraoxosulphate (VI) ions is its
reaction with acidified barium chloride to produce a white precipitate which is
insoluble in excess dilute hydrochloric acid. The acidification must be done to
prevent the precipitation of other insoluble barium salts such as BaCO3 and
BaSO3 which are soluble in excess dilute acid.
35.
The presence of a double bond indicates the functional group –
alkene. The double bond located at C-2 atom is named as (-2-ene). The longest
carbon chain has 5 C-atoms named as (pent). The branch chain is methyl group located at C-4 atom named as
(4-methyl). Combining the names in brackets in a reverse order gives:
4-methypent-2-ene [N.C.O]
36.
G5
37.
Alkene and alkyne can be distinguished from alkane by reaction
with KMnO4 or K2Cr2O7 and bromine water. Thus, both alkene and alkyne can
decolourize KMnO4. However, alkyne undergoes substitution reaction with
ammoniacal solutions of AgNO3 and CuCl while alkene does NOT [C]
38.
Sodium hydroxide on exposure to air absorbs carbon (IV) oxide to
form sodium trioxocarbonates and water which is alkaline. The equation for the
reaction is: 2NaOH + CO2 Na2CO3 +
H2O [C]
39.
Carboxylic acid consists of carbonyl group- CO and hydroxyl
group-OH. Combining the two gives : COOH
[D]
40.
Oxygen is the most abundant element on the erth surface. However
in the universe which consists of the earth and other planets, the stars, the
sun and the moon, hydrogen is the most abundant due to its high composition in
the sun and stars [E]
41.
All the hydrocarbons alkane, alkene and alkyne burns in excess air
to form CO2 and H2O. Among these hydrocarbons, only alkane doe NOT decolourize
bromine vapour. Thus X is an alkane [B]
42.
The products of combustion of X which is alkane are CO2 and H2O.
If Y one of the products of combustion of X which is alkane turns lime water
milky, then Y is CO2. If Z another product of combustion of X gives blue colour
with CuSO4, then Z is H2O. This is because CO2 reacts Ca(OH)2 to form CaCO3 which is milky and
water reacts with white anhydrous CuSO4 to form CuSO4 pentahydrate which is
blue [D]
43.
The equations for the heating of the following metals : Ca, Na,
Cu, Fe and Al in the air are :
2Ca + O2 2CaO
4Na + O2 2Na2O
2Cu + O2 2CuO
2Fe + O2 2FeO OR 4Fe +
3O2 2Fe2O3
4Al + 3O2 2Al2O3
From the above equation, iron (II) diiron (III) oxide are NOT
formed from heating Fe in the air. It is rather formed by
reacting red hot iron with steam.
44.
A metallic atom ionizes by
loss of electron while a metallic ion (cation) atomizes (changes into an atom)
by gain of electron. The cation- X2+ atomizes by gaining 2 electrons. From the
electronic configuration, number of electrons in X2+ = 18. The number of
electrons in its atom = (18 + 2) = 20.
Since atom is electrically neutral, the number of electrons = number of protons
= 20. Hence, the atomic number of X = 20
[C]
45.
Heating marble (CaCO3) to a very high temperature results in its
decomposition to CaO and CO2. The white solid quicklime (CaO) reacts vigorously
with water to form a slake lime (Ca(OH)2 which is an alkaline solution [E]
46.
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47.
A mixture of oil and hydrogen heated to a temperature of 1800C and
pressure of 5 atm in the presence of finely divided nickel as a catalyst yields
a solid fat. This is the process used in the synthesis of margarine and is
called hydrogenation. The hydrogen is introduced across the double bond in the
unsaturated carbon chains in the oil [A]
48.
Both Al3+ and Pb2+ form white precipitate soluble in excess
aqueous NaOH and insoluble in excess aqueous NH3. However, Pb2+ forms white
precipitate with concentrated HCl while Al3= does NOT [E]
49.
After the completion of
saponification reaction, concentrated NaCl is added to the soap solution to
reduce its solubility, harden the soap and separate it from propane-1,2,3-triol
(glycerol). This process is called salting out
[D]
50.
During vulcanization of rubber, sulphur atoms are added to form
strong cross-linkages which bind rubber molecules together thereby increasing
the durability, tensile strength and elasticity of the rubber over a wide range
of temperature [C]
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