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Neco 2018 Chemistry Theory & Objectives Answers – May/June Expo

By | On June 12, 2018 (6 months ago)

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 )

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 .

2KMnO 4( aq ) +16 HCl – — – > 2MaCl 2( aq ) +8H 2O ( s ) +5Cl 2( 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

P 1 = ( 745- 13. 5) mmHg = 731 .5mmHg

T 1 = ( 16+273 ) k = 289 k

P 2 = S . P = 760 mmHg

T 2 = S . T = 273 k

V 1 = 40cm ^ 3

using the general gas equation

P 1 V 1/ T 1= P 2 V 2/ T 2

V 2 = 731. 5* 40 * 273/ 760 * 289

V 2 = 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

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

6ai )

NH4^ +( aq ) + OH ^ -( aq ) +HCl ( aq ) — – > NH4 Cl ( aq ) +H 2 O ( 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. 1125 moles

solubility = 0. 1125 / 60* 100 = 1. 875mol / dm^ 3

6dii)

C 2 H 5OH ( aq ) +H 2SO 4( aq ) – — -> C 2H 5 HSO4( aq ) +H 2O ( i )

C 2 H 5HSO 4( aq ) — – -> C 2H 4( aq ) +H 2SO 4( 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 .

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

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)

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)

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

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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