Chemistry 2017 Waec Answers Essay/Obj Now Posted

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



ANSWERS LOADING........


Chemistry Obj



1ACDBCBDBCA

11DBAADCDBCB

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

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(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


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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


(4)

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:
=preserving food
=glazing pottery

5iib) Sodium trioxocarbonate(iv) is used for:
=standardizing acids in the laboratory
=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.

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