NECO 2018 Chemistry Obj And Essay Answer – June/July Expo

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NECO 2018 CHEMISTRY OBJ & THEORY ANSWERS

 

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AYOSTUFFS/A2 SOLUTION

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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'

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1bi)

CLICK HERE FOR THE 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)

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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

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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

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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

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3aii)

i)solubility

ii)boiling points

iii)densities

3aiii)

CLICK HERE FOR THE DIAGRAM

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3bi)

catalyst are substance which alter the rate of a chemical reaction but not themselves used up in the process.

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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

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3ci)

The solution turn from blue to white as a magnesium displace copper from its salt

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3cii)

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

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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

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3dii)

i)dissolving an acid on hydride in water

ii)combination of constituent element

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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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EQUATION IS REQUIRED IN No 4bi.

(4bi)

I. Limestone: The limestone decomposes when heated to yield carbon(iv)oxide which is a major reactant

Equation: CaCO3(s)  -->   CaO(s) + CO2(g)

II. Ammonia: The ammonia reacts with the carbon(iv)oxide to form ammonium hydrogen trioxocarbonate(iv)(g)

Equation: NH3(aq) + H2O(l) + CO2(g) --> NH4HCO3(aq)

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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)

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6aii)

the student got the choice of indicator wrong

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6aiii)

phenolphthalein is used when a strong base is present. aqueaous ammonia is a weak base

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6b)

i)gluclose and fructose

ii)invertase

iii)delivery tube

iv)glucose

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6ci)

white phosphorus and red phosphorus

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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)

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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

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6dii)

C2H5OH(aq) +H2SO4(aq)----> C2H5HSO4(aq)+H2O(i)

C2H5HSO4(aq)---->C2H4(aq)+H2SO4(aq) ethene

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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.

GOODLUCK!!!