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Chemistry
WAEC / WASSCE 2020
Kinetics, Energetics and Equilibrium
Solution
Which of the following statements is correet for a reaction at equilibrium?
A
All reactions cease to occur
B
The eaction has gone to completion
C
The rates of the forward and backward reactions are equal
D
The amount of product equals the amount of reactants
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
In a chemical reaction, chemical equilibrium is the state in which the forward reaction rate and the reverse reaction rate are equal. The result of this equilibrium is that the concentrations of the reactants and the products do not change.
Source: Myschool Past Questions Archive (Record #59000)
Chemistry
WAEC / WASSCE 2020
Acids, Bases, and Salts
Solution
Which of the following reactions are always exothermic? 1. Neutralization Il. Decomposition III. Combustion
A
I and II only
B
I and III only
C
II and IIl only
D
I, II and III
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
LIST OF EXOTHERMIC REACTIONS
any combustion reaction.
a neutralization reaction.
rusting of iron (rust steel wool with vinegar)
the thermit reaction.
reaction between water and calcium chloride.
reaction between sodium sulfite and bleach (dilute sodium hypochlorite)
reaction between potassium permanganate and glycerol.
Source: Myschool Past Questions Archive (Record #59001)
Chemistry
WAEC / WASSCE 2020
Matter & Separation Techniques
Solution
Which of the following standard conditions is not correct about energy changes?
A
Standard temperature is 298K
B
B. Standard pressure is 1 atm
C
Concentration of solution must be 1 mol/dm\(^3\)
D
ΔH at 298 K is the activation energy
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
the standard conditions of 1 atm pressure and 298K.
Source: Myschool Past Questions Archive (Record #59002)
Chemistry
WAEC / WASSCE 2020
Stoichiometry & Mole Concept
Solution
f 5.0 cm\(^-3\) of 0.200 mol dm(^-3\) Na\(_2\)CO\(_3\) was diluted to 250cm(^-3\) solution, what would be the concentration of the resulting solution?
A
0.004 mol dm(^-3\)
B
0.020 mol dm(^-3\)
C
0.200 mol dm(^-3\)
D
0.400 mol dm(^-3\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
=
initial molarity
=
initial volume in liters
=
final molarity
=
final volume in liters
0.200 X 5.00 = M\(_2\) X 250
M\(_2\) = 1 / 250
M\(_2\) = 0.004 mol dm(^-3\)
Source: Myschool Past Questions Archive (Record #59003)
Chemistry
WAEC / WASSCE 2020
Stoichiometry & Mole Concept
The initial volume and pressure of a given mass of gas is V and 3.P. What is its pressure if its volume is increased to 2V at constant temperature?
A
3 P
B
2P
C
\(frac{3}{2}\) P
D
\(frac{2}{3}\) P
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #59006)
Chemistry
WAEC / WASSCE 2020
Stoichiometry & Mole Concept
Solution
What volume of oxygen at s.t.p is required to burn completely 7.5 dm\(^3\) of methane according to the following equation?
CH\(_4\) \(_g\) + 20\(_2\) \(_g\) → CO\(_2\) \(_g\) + H\(_2\)O\(_g\)
A
3.75 dm\(^3\)
B
7.59 dm\(^3\)
C
15.0 dm\(^3\)
D
30.0dm\(^3\)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
1 mole of methane reacts with 2 moles of oxygen
1 vol of methane reacts with 2 vol of oxygen
: 7.5 vol of methane will yield 15 vol of oxygen in dm\(^3\)
Source: Myschool Past Questions Archive (Record #59038)
Chemistry
WAEC / WASSCE 2020
Acids, Bases, and Salts
When 250 cm3 of a saturated solution of CuSO\(_4\) at 30^\circC was evaporated to dryness, 5.0 g of the salt was obtained..
What is the solubility of the salt at 30^\circC? [CuSO\(_4\) = 160]
A
0.031
B
0.125
C
0.640
D
1.560
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #59040)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
The bond between NH\(_3\) and H\(^+\) in NH4\(^+\) is?
A
dative
B
covalent
C
hydrogen
D
electrovalent
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #59041)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
Which of the following oxides has a giant covalent structure?
A
Al\(_2\)O\(_3\)
B
Na\(_2\)O
C
P\(_4\)O\(_10\)
D
SiO\(_2\)
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
- Silicon dioxide is an example of a substance with a giant covalent structure . It contains many silicon and oxygen atoms. All the atoms in its structure are linked to each other by strong covalent bonds. The atoms are joined to each other in a regular arrangement, forming a giant covalent structure.
Source: Myschool Past Questions Archive (Record #59042)
Chemistry
WAEC / WASSCE 2020
Matter & Separation Techniques
Solution
Which of the following hydroxides is not readily soluble in water?
A
NH\(_4\)OH
B
Ca(OH)\(_2\)
C
NaOH
D
KOH
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
-The hydroxides of sodium, potassium, and ammonium are very soluble in water. The hydroxides of calcium and barium are moderately soluble.
Source: Myschool Past Questions Archive (Record #59044)
Chemistry
WAEC / WASSCE 2020
Matter & Separation Techniques
Solution
Which of the following statements about the solubility of a salt is correct?
A
A salt whose solubility increases with temperature would not crystallize easily on cooling
B
A salt whose solubility is independent of temperature would normally crystallize out on cooling
C
Crystallization would be efficient in separating out a salt whose solubility increases considerably with temperature
D
Solubility of a solid does not affect its crystallization
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Crystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound.
Source: Myschool Past Questions Archive (Record #59045)
Chemistry
WAEC / WASSCE 2020
Acids, Bases, and Salts
Solution
If 20 cm\(^3\) of sodium hydroxide was neutralized by 20 cm\(^3\) of 0.01 mol dm\(^3\) tetraoxosulphate(VI) acid, what is the concentration of the sodium hydroxide solution?
A
0.010
B
0.020
C
0.100
D
0.150
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
2NaOH + H\(_2\)SO\(_4\) → Na\(_2\)SO\(_4\) + 2H\(_2\)O
FRom the reaction, N\(_a\) = 1 ; N\(_b\) = 2
\(\frac{CaVa}{CbVb}\) = \(\frac{Na}{Nb}\)
\(\frac{{0.01}\times{20}}{{C_b}\times{20}}\) = \(\frac{1}{2}\)
cross multiply → C\(_b\) = \(\frac{{0.01}\times{20}\times{2}}{{20}\times{1}}\)
C\(_b\) = 0.02 mol/dm\(^3\)
Source: Myschool Past Questions Archive (Record #59048)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
"Electrons always occupy the lowest empty energy level" is a statement of
A
Aufbau Principle
B
Hund's rule
C
Pauli Exclusion Principle
D
Periodic law
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
- The Aufbau principle states that electrons fill lower-energy atomic orbitals before filling higher-energy ones
Source: Myschool Past Questions Archive (Record #59050)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
Which of the following metals does not react with water to produce hydrogen?
A
Copper
B
Potassium
C
Sodium
D
Zinc
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Most alkali metals and alkaline earth metals react with water to produce hydrogen. The alkali metals comprise Group 1 of the periodic table, and include lithium, sodium, potassium, etc.
- Zinc is not much reactive with cold or room temperature water but reacts with steam to form zinc oxide and liberate hydrogen gas.
- Copper lies below hydrogen in the activity series of metals, therefore it can not displace hydrogen from water
Source: Myschool Past Questions Archive (Record #59051)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
Which of the following arrangement of elements is in decreasing order of electronegativity?
A
Na, Mg, Al, Si, P
B
Na, A1, Mg, P, Si
C
P, Mg, Na, Si, Al
D
P, Si, Al, Mg, Na
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
- Reactivity series is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
-Very Electropositive Metals Most active metals have low electronegativities
Source: Myschool Past Questions Archive (Record #59052)