Expo: Chemistry (Essay & Objective) Waec 2017 Free Expo Answers See Here>>>>


 

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Tuesday, 18th April, 2017

Chemistry 2 (Essay) 2.00pm – 4.00pm
Chemistry 1 (Objective) 4.00pm – 5.00pm
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Chem

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21DBCBCCDBAD

31BACBACBCCD

41BDACABDABD

THEORY
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) Platinum
ii) Carbon

1h)
i) Hydrogen bonds
ii) Vander waals forces

1i) Water(H2O) and Carbonmonoxide (Co)

1j) 1s^2 2s^2 2p^6 3s^2 3p^6 3d^3 4s^2

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3)
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

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4)

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)
method
– rub the fat on a blank white paper
– pour Sudan (III) dye over the paper
-wash the paper under tap
Observation
– rubbing the fat on the paper produces a translucent color
-pouring sudan (III) will stain the blot red
Conclusion
– fat is present because sudan (III) can stain fat red


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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.

Chem

1ACDBCBDBCA

11DBAADCDBCB

21DBCBCCDBAD

31BACBACBCCD

41BDACABDABD

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