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WAEC 2019 Chemistry Theory and Obj Answers

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WAEC 2019 Chemistry Theory and Obj Answers by : 5:00 am On May 20, 2019

WAEC 2019 Chemistry exam will be holding today, Monday 20th of May, 2019. As we have been doing for other exams, we are here to help you with the Chemistry Theory and Objective Answers. The questions and answers are already out.To get it, buy MTN recharge card of N400 and send the pin, your phone number and subject paid for, to 09067385575.

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SEE CHEMISTRY ANSWERS FOR LAST YEAR’S WAEC

1ai)
Acid base indicator is a weak complex organic acid or base which gives different colours in acidic or basic medium
1aii)
-Methyl Orange
-Litmus
-Phenolpthalein
1bi)
-4Cu+2NO2->4CuO+N2=Oxidizing agent
-H20+2NO2->HNO3+HNO2=Oxidizing agent
1ci)
Enthalphy of combustion is the energy evolved when one mole of a substance burns completely in excess oxygen
1cii)
Because heat is always evolved
1d)
-Primary cell cannot be recharged after use but a secondary cell can be recharged after use
-Primary cells are irreversible while secondary cells are reversible
eg of primary cells are
-Daniel cell
-Leclanche cell
eg of secondary cell are
-Fuel cell
-Lead-acid accumulator
1e)
A mole is the amount of a pure substance containing the same number of chemical units as their atoms is exactly 12g of carbon -12 (ie 6.0210^23)
1f)
n=?
V=40cm^3
C=0.40mol/dm^3
n=CV/1000
=(0.40
40)/1000
=0.016mol
1g)
Carbon or graphite
Plantinum
1h)
– induced dipole – induced dipole interaction or dispersion force
-dispole- dispole interaction
1i)
– carbon(ii)oxide and water or co and H2O
1j) 26FE³+ — 1s²2s²2p^6 3s²3p^63d³4s²

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 across 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 )
(35)(17)Z=75%, (37)(17)Z=100-75=25%
Ar=(35537+37255)/100
=2625+9255/100
=3550/100
=35.5
2di )
-CO 2 by downward delivery
-HCL by downward delivery
H2 by upward delivery
2dii )
-because it is denser than air
-because it is denser than air

3ai )
Thermal cracking
3aii )
C4H 8
3aiii )
H H . H
| | |
H – C – C – C = C
| | | |
H H H and
-H H
| |
H – C – C = C – C – H
| | | |
H H H H
3aiv )
– normal butene
– But – 2 – ene
3av )
C4H 8 + H 2 -> C4 H 10
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

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.

5aii)
i)Sodium chloride is used for:
-preserving food
-glazing pottery

ii)
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

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