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Author Topic: Waec 2020 chemistry essay answer  (Read 2542 times)

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Offline Aebz

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Waec 2020 chemistry essay answer
« on: September 02, 2020, 02:32:06 pm »
(1ai)
Faraday’s First Law of Electrolysis states that the chemical deposition due to the flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.

(1aii)
Strong electrolytes ionize completely (100%), while weak electrolytes ionize only partially.

(1b)
CHEMICAL PROPERTY OF ETHYNE
– COMBUSTION REACTION: Ethyne burns in air with a luminous smoky flame and hence used for lightening purpose.
2C2H2 + 5O2 —–> 4CO2 + 2H2O + heat

(1c)
Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms.

(1cii)
CH3COOH + CH3OH–>CH3COOCH3 + H2O

(1ciii)
methly ethanoate

(1d)
By removing the main product continuously.

(1e)
Mzn = 3.75g
Mzn = 65.0g/mol
n= m/M=3.75/65.0
n=0.0577mole
nH² =0.0577mole because the mole ratio is the same
np =n*L
np=0.0577*6.02*10^23
np=3.47*10^22 moles

(1d)
Addition of catalysis I;e it catalyzed by a high concentration of hydrogen ion

(1f)
Flooding

(1gi)
Reaction C

(1gii)
Zinc (from + 2 to + 4)

(1hi)
(i)Each spectral line is caused by one electron
(ii)Electron can exist only in circular orbit of definite quantum energy.

(1hii)
It could not account for the spectrum at note complicated atoms

(1i)
(i)Temperature of the reacting system
(ii)Pressure of the reacting system
(iii)Concentration of the reacting system

(1j)
Both liberate carbon(iv) oxide
One produce a chloride salt , the other produce an ethronate salt

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #1 on: September 02, 2020, 02:41:59 pm »
2ai)
The relationship between the compounds A and B is that they have similar chemical properties

(2aii)
– A : Trans-1,2-dichloroethene
– B : Cis-1,2-dichloroethene

(2aiii)
Their chemical properties will be the same

(2aiv)
The reason is because they are geometric isomers. Geometric isomers have the same chemical properties but different physical properties.

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #2 on: September 02, 2020, 02:57:46 pm »
5a)
(i)ammonia (NH³)
(ii)hydrogen chloride gas(HCl)

(5aii)
The aim of the fountain experiment is to prove that HCI is highly soluble in water.

(5aiii)
The experiment consists of introducing water through an inlet to a container filled with ammonia gas. Ammonia dissolves into the water and the pressure in the container drops. As a result, more water is forced into the container from another inlet creating a fountain effect. In other words the water turns red.

(5bi)
(i)Petrochemical industries
(ii)Pharmaceutical industries.

(5bii)
(i)Pollution of water bodies by chemical waste
(ii)Pollution of the air
(iii)Radiation particles are released

(5ci)
(i)Coke
(ii)coal gas
(iii)Coal tar

(5cii)
(i)Coke- It is used to reduce iron oxide to produce iron.
(ii)Coal gas=>is used in lighting

(5di)
(i)calcium
(ii)magnesium

(5dii)
(i)reverse osmosis.
(ii)precipitation methods.

(5diii)
(i)Limescale (a hard crust) forms inside kettles.
(ii)This wastes energy whenever you boil a kettle. It helps to reduce heart disease.
==========================

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #3 on: September 02, 2020, 03:08:44 pm »
3. (a) Explain briefly the observations in each of the following processes:

(i) when carbon(IV) oxide is bubbled through lime water, it turns milky but the milkiness disappears when the gas is bubbled for a long time;

(ii) a precipitate of calcium hydroxide is insoluble in excess sodium hydroxide solution whereas that of lead.

(II) hydroxide is soluble.

(b) (i) What is a primary standard solution?

(ii) Calculate the mass of sodium trioxocarbonate(IV) required to prepare 250 cm3 of 0.15 moldm-3 solution.
[Na = 23.0; O = 16.0; C = 12.0]

(c) Name one gas that can be collected by:

(i) upward displacement of air;

(ii) downward displacement of air.

ANS: (a) (i): Insoluble CaCO3 formation is responsible for the milkness produce when CO2 is bubbled through lime water while the disappearance of milkness is due to the formation of soluble Ca(HCO3)2.
Lime water turns milky with CO2 because  CaCO3/ CaCO3(s)  is formed. Milkiness disappear when excess CO2 reacts with CaCO3 in water medium forming the soluble Ca(HCO3)2/ Ca(HCO3)2 (aq).
(ii) Calcium hydroxide is not amphoteric. Does not react with an alkali NaOH whereas lead (II) hydroxide is amphoteric so reacts with excess NaOH.

(b) (i) Primary standard solution is one whose concentration is known and can be used to standardize another solution.
(ii)    M (Na2CO3)    =  106 gmol-1
         m(Na2CO3)     =  C x M x V
                                   =   0. 15 x 106 x 0. 25
                                   =   3. 98 g                                 

 (c) (i) Carbon(IV) oxide, sulphur (IV) oxide, hydrogen chloride, oxygen, nitrogen (IV) oxide, chlorine, hydrogen sulphide.
(ii) Ammonia, oxygen, hydrogen, methane.
[8/18, 7:53 AM] +234 906 354 8595: 1. A is 0.100 mol dm-3 solution of an acid. B is a solution KOH containing 2.8 g per 500 cm3.
(a) Put A into the burette and titrate it against 25.0 cm3 portions B using methyl orange as indicator. Repeat the titration to obtain consistent titres.  Tabulate your readings and calculate the average volume of A used.

(b) From your results and the information provided above, calculate the:
(i) number of moles of acid in the average titre;
(ii) number of moles of KOH in the volume of B pipetted;
(iii) mole ratio of acid to base in the reaction
[H = 1.00, O = 16.0, K = 39.0]
[8/18, 7:56 AM] +234 906 354 8595: ANS: (a) titration answer soon.
.
(b) (i) number of moles of acid = 0.100 x VA
                                                                1000   
                                    =   X mole(s) [3sig. Fig to score]


                        1000cm3 contains 0.100 mole(s)
                    VA will contain 0.100 x VA
                                                     1000
                                    =   X moles [3 Sig. Fig. to score]       
.
(ii) Number of moles of KOH in B
                             500cm3 of B contains 2.8g of KOH
                       1000cm3 of B will contain 2.8 x 1000 = 5.6 KOH
                                                                           500 
                             Molar mass of KOH = 39 + 16 + 1 or 56 gmol-1

      Conc of B = 5.6  = 0.100 mol dm-3
                           56

(iii) Mole ratio of acid to base = X: Y to nearest whole number ratio.
.
2. C is a mixture of two salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion drawn from the result of each test.
.
(a) Put all of C into a boiling tube and add about 5cm3 of distilled water.  Stir thoroughly and filter. Keep both the residue and the filtrate.
.
(b) To about 2 cm3 of the filtrate, add few drops of Pb(NO3)2(aq)‑Boil the mixture and then allow to cool.
.
(c) (i) Put the residue in a test tube and add dilute HNO3. Shake the mixture and divide the solution into two portions.
.
(ii) To the first portion from (c)(i), add NaOH(aq) in drops and then in excess.
(iii) To the second portion from (c)(i), add aqueous ammonia in drops and thein in excess.

 3725: ANS:

TEST

OBSERVATION

INFERENCE

a)  C+water, mixture stirred
and filtered

Partly dissolves/ soluble Colourless filtrate
White residue (do not accept ppt /solid)

C contains soluble and insoluble salts

b) Filtrate + Pb (NO3)2(aq). Boiled then cooled

White precipitate formed
Precipitate dissolves
Precipitate re-appears

Cl-, SO42- or CO32.
Cl- present
Cl- confirmed

c) (i) Residue + dil HNO3

Effervescence /bubbles /gas evolved colourless, odourless gas. Gas turns lime water milky.

CO2 evolved from CO32.

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #4 on: September 02, 2020, 03:18:20 pm »
(2ai)
They are isomers

(2aii)
A - Trans 1,2 dichloroethane

B - Cis 1,2 dichloroethane

(2aiii)
Yes

(2aiv)
They contain the same functional group the single bond. The only difference is the polarity(physical property)
The Cis - polar compound while Trans-1, -di chloroethane is non polar

(2bi)
(i) Temperature remains constant during boiling
(ii) There is change of state during boiling

(2bii)
I - It will increase the boiling point of water.
II - It will reduce the boiling point of water.

(2biii)
Boiling occurs at a specific temperature While Evaporation occurs at almost all temperatures.

(2ci)
An unsaturated solution is one that contains less than the maximum amount of solute that can dissolve at a given temperature While A saturated solution is one that contains maximum of solute that can be dissolved in it at that temperature.

(2cii)
(i) By increasing the temperature of the solution.
(ii) By increasing the amount of the solute.

(2ciii)
Temperature.

(2di)
Mole is a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules, or other specified particles

(2dii)
 MgO(s)+2HCl(aq) ---> MgCl(aq)+H2O(l)
From the equation of reaction; 1 mole of MgO = 2 moles of HCl
Hence n = cv/100
where c = 0.1moldm-³; v = 25.0cm³
No of mole of HCl = n = 0.1x25/1000
= 2.5 x 10-³ moles
Hence the no of moles ofMgO required = 2.5/2 x10-³
But n = m/M = reacting mass/ Molar mass ---> m = nM = 1.25x10-³ x 40
= 50 x 10-³ = 0.05g of MgO.

(2e)
(i) They are malleable
(ii) They are ductile
(iii) They are good conductors of heat and electricity

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #5 on: September 02, 2020, 03:31:32 pm »
Obj:
01-10: CACCBDADAC
11-20: ACDCDABADA
21-30: BABACCBAAC
31-40: CBACBCDBAA
41-50: DBADCBBBCB

Offline Davidangyu

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Re: Waec 2020 chemistry essay answer
« Reply #6 on: September 02, 2020, 03:41:03 pm »
Bro Aezb you are good

Offline Aebz

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Re: Waec 2020 chemistry essay answer
« Reply #7 on: September 02, 2020, 04:03:30 pm »
3ai)
Draw the diagram

(3aii)
I. Activation Energy = (210 - 100)KJ = 110K
II. Hp - HR = ΔH
54 - 100 = -46KJ

(3aiii)
Q2(g) + R2(g) --> 2QR(g)

(3aiv)
Exothermic reaction.

(3av)
The heat content of the reactant is higher than that of the product.

(3bi)
E7 - 1s² 2S² 2P³
F9 - 1s² 2S² 2P⁵
G12 - 1S² 2S² 2P⁶ 3S²
H13 - 1S² 2s² 2P⁶ 3S² 3P¹

(3bii)
I. G and H
II. H
III. F
IV. GF2

(3ci)
Isotopy is the existence of an element in more than one physical form with the same atomic number but different atomic masses.

(3d)
(i) Atoms
(ii) Molecules
(iii) ions

Offline Lord AraB

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Re: Waec 2020 chemistry essay answer
« Reply #8 on: September 02, 2020, 04:33:22 pm »
CORRECT CHEMISTRY OBJ
1-10: CACDBDADAD
11-20: AADCDABBCD
21-30: BACBCCBCAC
31-40: CBACBCDBAD
41-50: DBBDCBCCCB
   
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    Offline Oz4U

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    Re: Waec 2020 chemistry essay answer
    « Reply #9 on: September 03, 2020, 09:32:50 am »
    Help with GOVT Essay Pls
    YWL-2

    Offline Sidikie Mansaray

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    Re: Waec 2020 chemistry essay answer
    « Reply #10 on: September 03, 2020, 09:46:45 am »
    Good morning here! Please help with “Government“ answers

    Offline JEK

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    Re: Waec 2020 chemistry essay answer
    « Reply #11 on: September 03, 2020, 09:52:03 am »
    we

     need government answer

    Offline Daniellaanderson

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    Re: Waec 2020 Government essay answer
    « Reply #12 on: September 03, 2020, 09:55:41 am »
    Good morning. Pls I need Government 2020 waec answer. Thanks!

    Offline NORTOLA

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    Re: Waec 2020 chemistry essay answer
    « Reply #13 on: September 03, 2020, 09:59:07 am »
    Government answers please

    Offline obinna12345

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    Re: Waec 2020 chemistry essay answer
    « Reply #14 on: September 03, 2020, 10:00:30 am »
    2)
    (i) Constitutional division of power: Powers are constitutionally shared between the central authority and other component units.
    (ii) Written and Rigid constitution: Codification of constitution on a single document/book which is difficult to amend.
    (iii) Powers derived from the constitution: The three tiers of government derived their powers from the constitution.
    (iv) Supremacy of the constitution: Constitution/law is strictly adhered as a regulation which everybody is subject to.
    (v) Separation of power: Adoption of the theory of separation of power which enables the arms of government to function independently in order not to have clash of powers.

    Offline obinna12345

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    Re: Waec 2020 chemistry essay answer
    « Reply #15 on: September 03, 2020, 10:02:48 am »
    Government

    2)
    (i) Constitutional division of power: Powers are constitutionally shared between the central authority and other component units.
    (ii) Written and Rigid constitution: Codification of constitution on a single document/book which is difficult to amend.
    (iii) Powers derived from the constitution: The three tiers of government derived their powers from the constitution.
    (iv) Supremacy of the constitution: Constitution/law is strictly adhered as a regulation which everybody is subject to.
    (v) Separation of power: Adoption of the theory of separation of power which enables the arms of government to function independently in order not to have clash of powers.

     

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