Neco 2017 Chemistry Theory & Obj Answers

Neco 2017 Chemistry Theory & Obj Answers Portal

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Chemistry OBJ:
1-10: ACBAEDCCAB
11-20: ECACDCADBC
21-30: ECCEBADADB
31-40: CABEBBABEA
41-50: DDDBAABDEB
51-60: CEEEECEEAA

(1ai)
(i)neutral to Litmus paper
(ii)Has a boiling point of 100°C

(1aii)
=[Na] / [Na2So4] × 100%
=23/ (23×2) +32+ (16×4) × 100%
=23/142 × 100%
=16.2%
Percentage of mass of a sodium
=16.2%
Also,
[O4] /[Na2SO4] × 100%
=(4×16) / 142 × 100%
=64/142 × 100%
=45.1%
Percentage of mass of oxygen
=45.1

(1aiii)
-Aluminum
(1iv)
-Bauxite (Al2O3 +2H2O)

(1bi)
I = (A) Is2 , 2s2 ,2p2
II= (B) Is2 , 2s2, 2p6,3s2
III=(C) Is2, 2s2, 2p6
IV=(D) Is2 ,2s2, 2p6, 3s2,3p5
V=(E) Is2, 2s2, 2p4

(1bi)
A Standard solution is a solution of known concentration.it is a solution containing known amount (in grams or mols) of a substance in a known volume of a solution.

(1bii)
A concentrated solution contains lesser molecule of water than a dilute solution

(1ci)
(i)simple sugar
(ii) complex sugar

(1cii) diagram
(1ciii)
Insert a glowing splinter into a test tube containing the unknown gas the rekindling of the glowing splinter indicates the presence of oxygen

(2ai)
(i)Oxidation is a process involving on loss of electrons
(ii)Reduction is a process involving the removal at electronegative elements as well as the addition of electro positive elements

(2aii)
(i)Nitrogen is a colourless,odourless and tasteless gas
(ii)it is slightly lighter than air

(2aiii)
X represents urea [(NH2)2Co)]
Y represents water[H2o]

(2bi)
Chlorine|35|17|18|1s^2 2s^2 2p^6 3s^2 3p^5
Fluorine|18|9|10|1s^2 2s^2 2p^5

(2bii)
No of moles= Mass/Molar mass
=5/25+16+1
=5/40
No of moles=0.125mole

(2biii)
Relative atomic Mass=
(18 × 1/3) + (20 × 2/3)
=19.3

(2ci)Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.

(2cii)
Single line represents the electrode/electrolyte reaction
– Double lines represents interface in the full cell

(2ciii)
Polymerization is the process whereby two or more monomers link together to form a compound of high molecular mass called the polymer

(2civ)
(i)It is used as a fuel in rockets
(ii)It is sometimes uses as an anti-freeze
(iii)it is used to dissolve soaps,perfumes etc

(3ai)
(i)high melting and boiling point
(ii)Good conductors of heat and electricity
(iii)Have characteristic lustre

(3aii)
Zn, Ca, Au, Pb
==========>
Increase

(3aiii)
Strong electrolytes ionize completely but weak electrolytes only partially ionizes.

(3bi)
Ethene is prepared from ethanol in two stage

1st stage==>heat ethanol with excess Conc H2SO4 acid at 170°C
C2H5OH(aq) + H2SO4 ==>C2H5HSO4(aq) + H2O(l)

2nd stage==>Heat the resulting ethyl hydrogentetraoxo-sulphate(iv)
C2H5HSO4(aq) ==>C2H4(g) +H2SO4(aq)

The Ethene produce is passed through Conc NaOH to remove impurities

(3ci)
(i)Mechinery should be improved so that more efficient fuel combustion occurs
(ii)People should be educated to make them aware of the causes and dangers of pollution

(3cii)
Efflorescent substance loses water to the surrounding with deliquescent substance absorbs and turn into solution

(3ciii)
(i)It is used for absorbing carbon(iv) oxide in the laboratory
(ii)It is used in making soap
(iii)it is used in refining petroleum

(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 walls of container

(4bii)
given that
P 1 = 320MMHg
P 2 = 760MMHg
V 1 = 220Cm ^ 3
V 2 =?
T 1 = 22°C
T 2 = 100°C
using P 1V 1/ T 1= P 2V 2/ T 2
V 2 = 320 × 220 × 100 / 22 × 760
V 2 = 7040000 / 16720
V 2 = 421. 05cm ^ 3

(4ci)
Daigram

(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 .

(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 pressures of 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)removal 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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