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Chemistry (OBJ & ESSAY) Neco 2017 Free Expo Answers




Chemistry (OBJ & ESSAY) Neco 2017 Free Expo Answers
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Thursday 6th July 2017
OBJ & Essay – Chemistry – 10am – 1pm
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*CHEMISTRY OBJ*

1-10ACBAEDCCAB
11-20ECACDCADBC
21-30ECCEBADADB
31-40CABEBBABEA
4159DDDBAABDEB
51-60CEEEECEEAA


1ai)
i)water is testeless,colourless and odourless
ii)the boiling point of water is 100'C
1aii)
Na2SO4=(23*2+32*1+16*4)=46+
32+64=132g
Na2 and O4=46+64=100g
%mass=100/sqr32*100 = 10000/132
=75.76%
1aiii)
i)aluminium
1aiv)
i)alumina
1b)
I = (A) Is2 , 2s2 ,2p2 ( Carbon)
II= (B) Is2 , 2s2, 2p4 (Oxygen )
III=(C) Is2, 2s2, 2p6 ( Neon)
IV=(D) Is2 ,2s2, 2p6, 3s2 ( Magnessium )
V=(E) Is2, 2s2, 2p6, 3s2, 3p5 (Chlorine)
1bi)
Element in Group Iv = A (Carbon)
Elements in S-block = D (Magnessium)
Element C not participate in chemical Rxn
Element E Readily Ionize & gain one electron
Elements B & D contain Two unpaired Electron
1bii)
Standard solution of a solute at a particular temperature is one which containing as much solution as it can dissolve at that termperature in the presence of undissoved solute particles
1biii)
dilute solution contains small amount of solute while concentratated solution contains large amount of solute
1ci)
i)manosaccharides
ii)disaccharides
iii)polysaccharides
1cii)
CLICK HERE FOR THE IMAGE
1ciii)
insert a glowing splinter into the unknown gas the rekindling of the glowing splinter indicates the presence of oxygen
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4ai)
i)addition of soda
ii)addition of zeolite
4aii)
the solubility of KCl increase at a constant rate with the rise in temperature while the solubility of NaCl is independent of temperature
4aiii)
PH of a solution is measure of the molar concentration of hydrogen ions in the solution
4aiv)
i)A is most acidic
ii) E is most basic
iii) C is neutral
4bi)
i)gases are made up of molecules which are in constant random motion
ii)the particles do not attract each other
iii)during motion the molecules of the gas collides with one another and with the wallss of container
4bii)
given that
P1=320MMHg
P2=760MMHg
V1=220Cm^3
V2=?
T1=22degree
T2=100degree
using P1V1/T1=P2V2/T2
V2=320*220*100/22*760
V2=7040000/16720
V2=421.05cm^3
4ci)
CLICK HERE FOR THE IMAGE
4cii)
i)it is used for respiration
ii)it is used in industries for removal of carbon sulphur and impurities in pig iron
iii)oxygen is used as propelants in space rocket.
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2ai)
oxidation is a process involving a loss of electron(s), Reduction is a process in which an electronagetive element loses electron while an electropositive element gains electron.
2aii)
i)nitrogen is colourless,ordourless and testsless gas
ii)it is slightly soluble in water
2aiii)
x is (NH2)2 CO
y is H20
2bi)
i)element-chlorine
E/configuration=1s^2, 2s^2, 2p^6 3s^2, 3p^5 atomic number is 9
ii)NaOH=(23*1+16*1+1*1)
=23+16+1=40g
avogrado's constant=6.02*10^23
5g=5/40*6.02*10^23
=6.02*10^23=0.753*10^23
=7.53*10^22moles
iii)fractional abundance
=1/3 and 2/3
=1/3 * 18 + 2/3 * 20
=18/3+40/3=58/3
=19.33g
2ci)
faraday's second law of electrolysis states “When the same quantity of electricity is passed through different electrolytes, the masses of different ions liberated at the electrodes are directly proportional to their chemical equivalents (Equivalent weights).
2cii)
the single line represents one electron while double bonds represent two electrons
2ciii)
polymerization is any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule, called a polymer.
2civ)
i)it is used for making wine,beer,etc
ii)it is used as fuel
iii)it is used as preservative and steriling liquids
iv)it used for making anti-freeze reagents in automobile radiators
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6ai)
I)solution A is starch solution, sample B is Iodine
II)the colouration is formed due to the formation of an Iodine starch complex
III)
i)Iodine is used in treatment of goitre
ii)Iodine is used in making dye for colour photography
6aii)
dalton's law of partial pressure states that in a mixture of non-reacting gases, the total pressureexerted is equal to the sum of the partial pressuresof the individual gases.
6bi)
C - 4.08/12, H - 0.68/1, O - 5.46/16
0.34/0.34, 0.68/034, 0.34/0.34
1, 2, 1.
The emperical formula is CH2O
6bii)
( CH2O)n =60
((12*1)+(1*2)+(16*1))n=60
(12+2+16)n=60
30n/30=60/30
n=2
(CH2O)2=C2H4O2
the molecular formular is C2H202
6ci)
i)exothermic reaction
ii)A is activation energy, B is DH(Negative)
6cii)
i)removeal of carbon(iv)oxide
ii)liquetying the air
6ciii)
vander waal forces
6di)
fats have higher melting point than oil because fats are more denser
6dii)
i)it is poisonous
ii)it is 2,5 times denser than air
iii)it is greenish-yellow gas with a choking smell
6diii)
Zn^2+ has comppletely filled d-orbitals and there are no vacant d-orbitals for the transition of electrons while Sc^3+ has completely empty d-orbital and there are no electrons for d-d transition thus they are colourless
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