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Chemistry (Essay & Objective) Waec 2017 Free Expo Answers

Tuesday, 18th April, 2017

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