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Wednesday, June 12, 2019

NECO 2018 CHEMISTRY OBJ & THEORY/ESSAY QUESTION AND ANSWERS RUNZ

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NECO 2018 CHEMISTRY OBJ & THEORY/ESSAY QUESTION AND ANSWERS RUNZ

CHEMISTRY OBJ:
1-10: DADBCADBCA
11-20: DCDBDBEDDC
21-30: CBDEDBAAEA
31-40: ECCADAEDEB
41-50: EAADDACBBC
51-60: ADDDBACBEB


============

(1a)
I. Isotopy is a phenomenon whereby an atom of an element excite different mass number but have the same atomic number.
II. Isomerism is existent of two or more compound (known as isomers) with the same molecular formulae but different molecular structure

(1aii)
(i) Deuterium
(ii) Tritium

(1bi)
DIAGRAM

Bottomed flask and set up the apparatus as shown. Add conc HCl gradual into the flask through the thistle funnel pass the gas produced through water and concentrated tetraoxosulphate (iv) and collect it by downward delivery.
2KMnO4(aq)+16HCl---->2MaCl2(aq)+8H2O(s)+5Cl2(aq)

(1bii)
(i) It is use as a bleaching agent
(ii) It is use as disinfectant in the treatment of water
(iii)it is use as an oxidizing agent

(1ci)
GIVEN
P1=(745-13.5)mmHg =731.5mmHg
T1=(16+273)k=289k
P2=S.P=760mmHg
T2=S.T=273k
V1=40cm^3
using the general gas equation
P1V1/T1=P2V2/T2
V2=731.5*40*273/760*289
V2=36.4cm^3
The volume of the gas at S.T.P is 36.4cm^3

(1cii)
(i) Nature of reactions
(ii) Presence of a catalyst

===============================================





(3ai)
A homologous series is a family of organic compound which follows a regular structural pattern in which each successive member differ in its molecular formula. By-CH2-GROUP

(3aii)
(i) Solubility
(ii) Boiling points
(iii) Densities

(3aiii)
DIAGRAM

(3bi)
A catalyst is a substance which alter the rate of a chemical reaction without itself being used up in the process.

(3bii)
(i) They are proteinous in nature 
(ii) They alter the rate of a chemical reaction
(iii) They remain unchanged in the reaction

(3ci)
The solution turn from blue to white as a magnesium displace copper from its salt

(3cii)
Mg(aq)+CuSO4(aq)-----> MgSO4(aq)+ Cu(s)

(3di)
Equation Reaction:
2Na(s)+O2(q)----->Na2O2(s)
Number of moles of soduim =mass/molar mass =5.95/23=0.2587moles
Reactive ratio of sodium to its oxide is 2:1
Therefore number of moles of Na2O2=0.2587/2=0.129moles
Mass of oxide 
=0.129*[(23*2)+(16*2)]
=0.129*78
=10g

(3dii)
(i) Dissolving an acid anhydride in water
(ii) Combination of constituent element

(3diii)
Washing soda (NaCO3. 10H2O)

========================
4ai)
From the collision theory the rate of chemical reactions depend on the frequency of effective collisions cones that the result in reaction between reactant particles
4aii)
cracking means breaking down or decomposition of a compound by the action of heat alone. while Reforming is the breaking down of a compound by the use of a catalyst
4aiii)
they are the most important processes for the commercial production of gasoline and diesel fuel

4bi)
I. Limestone: the limestone decomposes when heated to yield carbon(iv)oxide which is a major reactant
II. Ammonia: The ammonia reacts with the carbon(iv)oxide ammonium hydrogen trioxocarbonate(iv)

4bii)
I. B belong to the class of compound called carbohydrates
II. C is ethanol [C2H5OH] , D is ethylethanoate [CH3COOC2H5]
III. Functional group is -OH
IV. CH3COOH(aq)ethanoic acid + C2H5OH(aq)c ----->conc H2SO4(catalyst) -----> CH3COOC2H5(i) + H2O(i)

4ci)
CH(CH3)3,CH3CH2CH2CH3,CH3CH2CH2CH2OH/Increasing boiling points

4cii)
i)Bubbles formed at the bottom of liquid rise to the surface 
ii)temperature remain steady

4ciii)
I. Addition of sodium chloride crystals raises the boiling point of water
II. Reduction in atmospheric pressure lowers the boiling point of water

4civ)
I. N2O has oxidation state of +1 for Nitrogen
II. NO has oxidation state of +2 for Nitrogen
III. NO2 has Oxidation state of +4 For Nitrogen


=======================




(6ai)
NH4^+(aq)+OH^-(aq)+HCl(aq)---> NH4Cl(aq)+H2O(l)

(6aii)
The student got the choice of indicator wrong

(6aiii)
Phenolphthalein is used when a strong base is present. Aqueaous ammonia is a weak base

(6b)
(i) Gluclose and fructose
(ii) Invertase
(iii) Delivery tube
(iv) Glucose

(6ci)
White phosphorus and red phosphorus

(6cii)
I. Has no effect of red litmus paper
II. changes damp blue litmus paper pink
III. Reacts directly with alkali to yield a trioxocarbonate(iv)

(6di)
GIVEN:
mass of P= 9g
molar mass of P =80g/mol
: Number of mole of P presnt =mass/molar mass
=9/80=0.1125moles
solubility =0.1125/60*100=1.875mol/dm^3

(6dii)
C2H5OH(aq) +H2SO4(aq)----> C2H5HSO4(aq)+H2O(i)
C2H5HSO4(aq)---->C2H4(aq)+H2SO4(aq) ethene

(6diii)
Bromine Exists as liquid at room temperature because there is decrease in votality down the group of the halogens due to increasing strength of the van der waal's force.

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