NECO 2018 Chemistry Essay and OBJ Expo

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

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

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2a)
A=1s^2,2s^2,2p^6,3s^2,3p^5
B=1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3^9
2aii)
i)it is very mulleble
ii)it is an excellent conductor of heat and electricity
iii)it a red solidd with lustre
2aiii)
the oxidation state is -1
2b)
i)mecury
ii)propan 1, 2diol
iii)poly ethene
2c)
i)iron(iii)trioxocarbonate(iv)
ii)Zinc sodium hydroxide
iii)2Chloro but – 3 diene
2d)
i)Chalk- calcium carbonate
ii) glass- silica sand
iii) ceramics- kaolin/iron oxide/aluminum or sodium carbonate
2ei)
Faraday first law of electrolysis state that the mass of an element or substance (m) liberated at the electrode during electrolysis is directly proportional to the quantity of electricity (N) passing through it.
Q<M M=Zit
where M=mass, Z is constant, I is current
2eii)
4OH—->2H2O+O2+4e
from the oxidation half reaction of acidified water above it can be reduced that 4moles of electrons result to the formation of 1mole of oxygen
;4F=4*96,500C=386000
I=2.5A
t=1.5*60=90second
Q=It=2.5*90=225C
;386000 require 22.4dm^3
225c will require 22.4*22.5/386000
=0.0131dm^3
or 13.10cm^3
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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)
1)Each successive member differ in relative molecular mass by an increase of 14.

2)chemical properties of the member are similar but with a gradual variation along the series.

3) each successive member in a series differ in molecule formula by the addition of a -CH2 group .

3aiii)

3bi)
catalyst are substance which alter the rate of a chemical reaction but not themselves used up in the process.
3bii)
i) they are proteinous in nature
ii)they alter the rate of a chemical reaction
iii)they are not use themselves up 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 on hydride in water
ii)combination of constituent element
3diii)
washing soda (NaCO3. 10H2O)

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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

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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

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4aiii)
they are the most important processes for the commercial production of gasoline and diesel fuel

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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)

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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)

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

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4cii)
i)Bubbles formed at the bottom of liquid rise to the surface

ii)temperature remain steady

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

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