2020/2021 WAEC/NECO Answers: Chemistry answers. Neco Gce 2021



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(2)

Electrolytes are the components that conducts electricity in molten form or in solution e.g Nacl solution, CuSO

Cu2+ SO42-

Electrolysis is the chemical decomposition of a substance brought about by a direct current passing through either a solutions of or a Molten form.


(2ii)

Elements that are electolytically reduced are sodium Na, Potassium, Calcium Ca.


(2b)

11R and 17S

(i) Na and Cl ==> Sodium Chloride Nacl

(ii) Covalent land 


(2bii)

(i) Bleaching Agents

(ii) for making important chemicals such as Hcl


(2iv)

(i) 11R ==> Sodium has low I.E

(ii) Fe (iron) react with cold water to form Iron (iii) tetroxide with the release of hydrogen but slow of the iron not hot


(2ci)

Cold water on sodium, hydroxide forms at first rate but explode with hot water


(2cii)

When water is added to blue anhydrous copper (ii) chloride the colour changes from blue to pink  


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



(3ai)

Gay Lussac’s Law of combining volumes states that if gasses react they do so in volume which bears a simple ratios and to the volume of the product. If gaseous provided that the temperature and pressure remains constant


(3aii)

V1 = 250cm3

T1 = 250c

T2 = ?

V2 = 2v1

= 25 + 273

= 2 x 250cm3

= 298k

= 500cm3


V1/T1 = V2/T2

250/298 = 500/T2

250 T2 = 500 x 298

T2 = 500 x 278/250

= 596k


(3bi)

Atomicity of an element is the total number of atoms present in one molecule of an element or a compound 


(3bii)

- Monatomic has --> Helium, Neon

- Triatomic Gas --> Ozone O3


(3biii)

- it is used as antiseptic 

- it is in bleaching delicate materials such as Silk, wool, pulp etc


(3v)

- it is a colourless, odourless gas

- it is neutral to moist litmus paper


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


(4ai)

- to get the reduction of impurities 

- to avoid other constituents to stick to them


(4aii)

CuCO3(s) D--> CuO + CO2

1mole of CuCO3 produce 1 mole of CO2 

0.081 mole would give 0.081 moles of CO2

No of mole = mass/molar mass

= 10/123.5 

= 0.081 moles 

CuCO3 ==> 123.5

No of mole of CO2 = Volume given/22.4

0.081 = volume/22.4

V = 22.4 x 0.081

= 1.8144dm3


(4bi)

TABULATE:

Endothermic | Exothermic

UNDER EDOTHERMIC

(1) heat is absorbed to the surroundings

(2) The Enthalpy change is posture (+ve)

UNDER EXOTHERMIC:

(1) Heat is evolved to the surroundings

(2) The enthalpy changes here is negative


(4bii)

(i) Sodium hydroxide pellets in water is Exothermic 

(ii) Ammonium Chloride in water is Endothermic

(iii) Con H2SO4 acid is Exothermic


(4ci)

TABULATE:

Saturated Fatty Acids | Unsaturated Fatty Acids

UNDER SATURATED FATTY ACIDS:

- Their bonds to accepts any form of constituents are full

UNSATURATED FATTY ACIDS:

- they still have more bond space so they are Unsaturated 

(4cii)

Fatty acid are work acids because they dissociate partially in water and the Hydrogen or Hydroxonium ions are not concentrated



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