WAEC GCE 2019 - CHEMISTRY ANSWER

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CHEMISTRY OBJ
1-10: ACBDDCBBCB
11-20: ACBAADCBDC
21-30: DACCAADBCC
31-40: ACADCDCCDD
41-50: ABCDBCCBBA

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ANSWERS:

(1a)
An ion is a charged atom. It is a negatively or positively charged atom. It is formed when an atom loses or gains electrons.

(1b)
(i) Sand bed: It is used as a filtration step in treatment of river water.
(ii) Chlorine: It is used as disinfectant (kills germs) in the treatment of water.
(iii) Alum: It is used in the coagulation of dirt particles in a sample of water.

(1c)
(i) The number of particles.
(ii) The energy of the reacting or colliding particles.


(1d)
Palm wine turns sour after some days due to the fermentation of glucose to alcohol through the process known as fermentation, which further oxidation turns to ethanoic acid.

(1e)
(i) Acids react with metals to form salt and hydrogen gas liberated.
(ii) They react with bases to form salt and water.

(1f)
(i) electroplating of the metal.
(ii) the use of alloy.

(1g)
(i) Be
(ii) Li and F

(1h)
Pv = nRT
R = Pv/nT
= 1.0132 × 10^5 × 22.4/1 × 273.14
= 8309.17dm³Nm-²mol- k-



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(3ai)
Structural formula is one which shows the araangemt of atoms in the molecules.

(3aiï)
Draw the hydrocarbon

(3aiii)
Pentane; 2-methylbutane; 2,2-dimethyl propane.

(3bi)
(i) He observed that alpha particles scattered at varying degrees.
(ii) A visible flash of light was produced.

(3bii)
That atom consists of a positive core called nucleus, where most of the mass of the atom is contained and electrons which move around the nucleus.

(3ci)
(i) Law of conservation of mass : It states that matter is neither created nor destroyed during chemical reaction but changes from one form to another.

(ii) Law of definite proportions : It states that all pure samples of a particular chemical compound contain silver elements combined in the same proportion by mass.

(3cii)
(i) Temperature
(ii) Presence of oxygen
(iii) The solubility capacity of the ionic solid

(3ciii)
CO2 is gas but SiO2 is solid because the SiO2 is in giant molecular structure but the CO2 is simple molecular structure. And SiO2 has a melting whereas CO2 has a low melting point.

(3di)
I. Acidic ---> X(with PH 5)
II. Basic ---> Y(with PH 2)

(3dii)
Decreasing order of dissociation : Y, Z, X

(3diii)
Strong acids completely ionizes in water. The strongest the acid the higher the dissociation



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(4ai)
(i) MnO2
(ii) H2SO4
(iii) NaCl

(4aii)
MnO2 + 2NaCl + 2H2SO4 --> MnSO4 + Na2SO4 + 2H2O + HCL

(4aiii)
If we put an unknown gas into gas jar containing HCL, a rotten egg produce from the jar indicate the presence of hydrogen chloride gas.

(4bi)
(i) It is malleable.
(ii) It is ductile.
(iii) It is sonorous.

(4bii)
Oxidizing agent
Cu + 2H2SO4 --> CuSO4 + SO2 + 2H2O
Dehydrating agent.

C2H5OH + H2SO4 --> C2H5 HSO4 + H2O

(4ci)
C + 2H2O ---> CO + H2
[water gas]
= CO Carbon(II)Oxide and H2 Hydrogen

(4cii)
(i) Carbon.
(ii) Oxygen.
(iii) Hydrogen.

(4ciii)
(i) Coal tar.
(ii) Coal gas.

(4di)
NaNO3 ---> NaNO2 + O2(gas)

(4dii)
I - SO3
II - Al2O3

(4diii)
N2O3 + H2SO4 --> Al2(SO4) + H2O

Al2O3 + NaOH ---> NaOH + Al2SO4 + H2O

(4e)
(i) It is used as a chalk.
(ii) It is used in Iron making industry.

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(5ai)
Alloptropy can be defined as the existence of two or more different physical forms of a chemical element.

(5aii)
(i) Carbon
(ii) Sulphur

(5aiii)
TABULATE THE DIFERENCES:

Rhombic:
(i) Density of 2.06g/ml
(ii) It is stable at temperature below 96°c
(ii) Octahedral crystals

Monoclinic:
(i) Density of 1.97g/ml
(ii) Unstable attemperature below 96°c
(iii) Needle like long crystals

(5bi)
Neutralization can be defined as a reaction between an acid and a base to produce salt and water only

(5bii)
2.5 mol/dm^3 of the NaO3 is dissolved in 50cm^3 of 2.0mol/dm^3 trioxonitrate(v)acid

(5ci)
Na+,Cl-,H+,OH-

(5cii)
-At cathode - hydrogen
-At anode - chlorine gas

(5ciii)
At cathode: 2H+ + 2e- --->H2(g)
At anode: 2Cl- ---> Cl2+2e-

(5civ)
It turns the solution yellow

(5v)
It is used in the production of chemicals

(5di) This is because it dissolves most substances ie solute substances

(5dii)
TABULATE THE DIFFERENCE:

EVAPORATION:
(i) It occurs at surface of liquid
(ii) It occurs at all temperature

BOILING:
(i) It occurs throughout the liquid
(ii) It occurs at a certain temperature


(5diii)
Freezing







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ANSWER LOADING......
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