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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)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
The metallic bond in magnesium is stronger than that in calcium because magnesium has a
A
larger atomic size.
B
smaller atomic size
C
greater number of valence electrons
D
lower melting point
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
- Magnessium has a stronger metallic bond than calcium because it has smaller atomic radius.
- Atomic radius decreases across a period and increases down a group.
Source: Myschool Past Questions Archive (Record #59054)
Chemistry
WAEC / WASSCE 2020
Matter & Separation Techniques
Consider the reaction represented by the following equation:
AgNO\(_3\) + NaCl → AgCl + NaNO\(_3\).
The steps that could be taken to obtain pure dry sample of AgCI (s) from the mixture includes
A
heating to saturation and drying
B
filtering and evaporation to dryness
C
filtering, washing and drying
D
crystallizing and allowing to cool
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 #59055)
Chemistry
WAEC / WASSCE 2020
Atomic Structure and Periodic Table
Solution
How many electrons does \({31}_{15}\)P\(^3-\) contain?
A
12
B
15
C
16
D
18
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
- Phosphorus also has 15 electrons.
- Here we have P3- which means that this atom has gained 3 electrons. So, P3- has 18 electrons.
Source: Myschool Past Questions Archive (Record #59061)