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Waec 2017 Chemistry Obj And Theory Answers – May/June Expo

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Chem-Obj
1DCDBCBBADD
11DAACDCDBCB
21ADCACCDBAB
31BACBACCCCD
41BDACABDABD
==========================
THEORY
3ai)
Thermal cracking
3aii)
C4H8
3aiii)
(I) H H. H
| | |
H-C-C-C=C
| | | |
H H H H
and
(II) H H
| |
H-C-C=C-C-H
| | | |
H H H H
3aiv)
I-normal butene
II -But-2-ene
Ni
3av)
C4H8 +H2 ——-> C4H10
250c
3b)
in other words the oil is stained
red. This is a aspecifit test for fats
if suden (iii) is added to fats a
distinct red colouration is
observed
3c)
Given 2502+02+2H20—>2H2SO4
1mole produce 2mole
1.3mole produce 3mole
moles of H2SO4=3mole
molar mass of H2SO4=
(1+2)+32+(4*16)
=2+32+64
=98gmol-^1
mole=mass/molar mass
mass and H2SO4=Mole*molar
mass
=3*98
=294g
3di)
DH2<DH3<DH1
==========================
2a)
i)periodic law states that
properties of elements are the
periodic function of their atomic
number
ii)periodic property of element is
the variation of the properties of
element in a regular pattern both
down the group and acrose the
period
2aii)
i)ionization energy
ii)electron affinity
iii)electropositivity
2aiii)
ionization energy increase from
left to right acrose a period
because the nuclear charge
increase progressively while the
screening effect remain constant
-atomic reduis decreases from left
to right acrose the period because
nuclear charge effect out weighs
screening effect,which remains
constant because the number of
shell in a period is constant
-electron affinity increase from left
to right across a period because an
additional electron will experience
a greater repulsion than altraction
from the positively charged
nucleus
2b)
the relative atomic mass of an
element is the mass of one atom
of the element compared with the
mass of an atom of the carbon -12
isotope whos mass is exactly 12
2bci)
isotopy
2cii)
the isotopes have difference
number of neutron
2ciii)
R.A.M=(75/100*35)+(25/100*37)
=2634.25
2di)
I CO2 by downward delivery
II HCL by downward delivery
III H2 by upward delivery
2dii)
I because it is denser than air
II because it is denser than air
==========================
1ai)
an acid base indicator is a weak
acid or weak base that exhibits a
colour change as the
concentration of hydrogen (H^+)
or hydroxide (H^-) ions changes in
an aqueous solution
1aii)
methyl-orange
1b)
i)oxidizing agent
ii)mixed anhydride
1c)
enthalpy of combustion is the heat
evolved when one mole of a
substance is completely burns in
oxygen gas under standard
conditions
1cii)
enthapy of combustion is always
negetive since it involvs a rise in
temperature and heat of reactants
is greater than the heat of
products
1d)
primary cell is a cell that cannot be
re charged while secondary cell is
a cell that can be recharged
1dii)
primary cell — daniell cell
secondary cell — lead accumulator
1e)
mole is the unit of measurement
in the International System of
Units (SI) for amount of substance.
The unit is defined as the amount
of a chemical substance which
contains as many representative
particles, e.g., atoms, molecules,
ions, electrons, or photons, as
there are atoms in 12 grams of
carbon-12 (12C), the isotope of
carbon with relative atomic mass
1f)
n= V=40cm^3
c= 0.40moldm^3
n=cv/1000
0.40*40/1000 = 0.016mol
1g)
i)carbon or graphite
ii)platinum
1h)
i)induced dipole-induced dipole
interaction or dispersion force
ii)dipole-dipole interaction
1i)
i)carbon(ii)oxide and water or CO
and H20
1j)
2bFe^3+-15^2,2s^2,2p^6,3s^2,3p^6,3d^3,4s^2
==========================
5ai)
worm the unknown substance
with concentrated H2SO4 in a test
tube. if trioxonitrate(v) ion’s are/is
present, some trioxonitrate(v) acid
will be condensed as oily drops on
the upper part of the tube. On
further heating, the acid
decomposes yielding brown fums
of NO2 gas.
5iia)
Sodium chloride is used for:
i)preserving food
ii)glazing pottery
5iib)
Sodium trioxocarbonate(iv) is used
for:
i)standardizing acids in the
laboratory
ii)the manufacture of glass
5bi)
C(s) + O2(g) =====> Co2(g)
Co2(g) + C(s) =====> 2Co(g)
Fe2O3(s) + 3Co(g) =====> 2Fe(l) +
3Co2(g)
The limestone present
decomposes as follows:
CaCo3(s) =====> CaO(s) + Co2(g)
Which is available to remove
silicon(iv) oxide impurity
SiO2(s) + CaO(s) =====> CaSiO3(s)
5bii)
Faraday’s first law of electrolysis
states that, the mass (m) of an
element discharged during an
electrolysis is directly proportional
to the quantity of electricity (Q)
passing through it.
==========================
Completed.

 

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