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Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
Solution
A sample of air was bubbled into water. The PH of the water slowly changed from 7 to 6. Which of the following gases in the samples caused the change?
A
carbon(iv)oxide
B
carbon(ii)oxide
C
nitrogen
D
oxygen
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
An acid gas is any gaseous compound which, when dissolved in water, will form an acidic solution
The most common acid gases are hydrogen sulfide (H2S) and carbon dioxide (CO2) gases
Source: Myschool Past Questions Archive (Record #58113)
Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
Solution
The most suitable indicator for the reaction between NaOH and HCOOH is?
A
bromocresol
B
methyl orange
C
methyl red
D
phenolphthalein
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Phenolphthalein is suitable as indicator for this reaction i.e strong base and weak acid
Source: Myschool Past Questions Archive (Record #58117)
Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
Solution
which of the following pairs of substances has the highest heat of neutralization?
A
strong acid and strong base
B
weak acid and weak base
C
strong acid and weak base
D
weak acid and strong base
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
In other terms, the stronger the acid the greater the amount of hydrogen ions present in the solution, and hence the more alkali that should be required to neutralise the solution, hence increasing the enthalpy
Source: Myschool Past Questions Archive (Record #58131)
Chemistry
WAEC / WASSCE 2019
Kinetics, Energetics and Equilibrium
Solution
When quicklime dissolves in water?
A
heat is absorbed
B
heat is evolved
C
oxygen is liberated
D
hydrogen is given off
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
- When quicklime is added to water, it forms slaked lime along with the evolution of heat. There will be a rise in the temperature of the bucket. Calcium oxide reacts with water to form calcium hydroxide, also called slaked lime.
- That is adding water to quicklime produces an exothermic reaction (gives out heat) and hydrated lime.
Source: Myschool Past Questions Archive (Record #58135)
Chemistry
WAEC / WASSCE 2019
Matter & Separation Techniques
Solution
If the value of \DeltaH is positive for a reaction, it means that the reaction is?
A
exothermic
B
endothermic
C
spontaneous
D
slow
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
- Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products.
- A system of reactants that absorbs heat from the surroundings in an endothermic reaction has a positive \DeltaH.
- examples of endothermic processes:
Melting ice cubes.
Melting solid salts.
Sublimation of dry ice into carbon dioxide gas.
Evaporating liquid water.
Source: Myschool Past Questions Archive (Record #58160)
Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
Solution
Which of the following compounds is formed by the oxidation of ethanol?
A
C\(_2\)H\(_4\)CO\(_2\)H
B
C\(_2\)H\(_5\)CO\(_2\)H
C
CH\(_3\)OH
D
CH\(_3\)CO\(_2\)H
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
-Potassium dichromate solution is acidified with dilute sulphuric acid to oxidise ethanol into ethanoic acid.
Source: Myschool Past Questions Archive (Record #58161)
Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
Solution
What is the characteristic of the gas liberated when dilute hydrochloric acid is added to Iron(ii)sulphide?
A
turns lime water milky
B
decolorizes bromine water
C
gives a pop sound
D
turns lead(ii)ethanoate paper black
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
- Iron sulfide reacts with hydrochloric acid, releasing hydrogen sulfide: FeS + 2HCl → FeCl\(_2\) + H\(_2\)S.
- Hydrogen sulfide reacts with lead acetate to form lead sulfide and thus produces a coloration on the paper which will vary from yellow to black, depending upon the amount of hydrogen sulfide present.
Source: Myschool Past Questions Archive (Record #58162)
Chemistry
WAEC / WASSCE 2019
Stoichiometry & Mole Concept
Solution
An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. What is the empirical formula of the compound?
[ H = 1.0. C = 12.0, O = 16.0 ]
A
C\(_3\)H\(_8\)O
B
C\(_6\)H\(_{12}\)O
C
C\(_6\)H\(_{12}\)O\(_2\)
D
C\(_{12}\)H\(_{12}\)O\(_{11}\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
C = 72 / 12 H = 12 / 1 O = 16 / 16
C = 6 H = 12 O = 1
: EMPIRICAL FORMULA
C\(_6\)H\(_{12}\)O
Source: Myschool Past Questions Archive (Record #58163)
Chemistry
WAEC / WASSCE 2019
Organic Chemistry
Solution
When excess chlorine is mixed with ethane at room temperature, the product formed is?
A
1,2-dichloroethane
B
1,2-dichloroethene
C
1,1-dichloroethane
D
1,1-dichloroethene
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
- The chemical compound 1,2-dichloroethane, commonly known as ethylene dichloride (EDC), is a chlorinated hydrocarbon
Source: Myschool Past Questions Archive (Record #58165)
Chemistry
WAEC / WASSCE 2019
Organic Chemistry
Solution
Which of the following reagents could be used to distinguish between propan-1-ol and propan-2-ol ?
A
H+ / K2Cr2O7
B
I\(_2\) / OH\(^-\)
C
CH\(_3\)COOH
D
NaCl
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The reagent I\(_2\) / OH\(^-\) (iodine in alkaline solution) is used for the iodoform test, which identifies compounds containing a methyl ketone group or a methyl hydroxy group (specifically a secondary alcohol with the structure CH\(_3\)CH(OH)R).
Propan-2-ol is a secondary alcohol (CH\(_3\)CH(OH)CH\(_3\)) that possesses the required methyl group adjacent to the hydroxyl-bearing carbon. It reacts with I\(_2\) / OH\(^-\) to produce a characteristic yellow precipitate of iodoform (CHI\(_3\).
Propan-1-ol is a primary alcohol (CH\(_3\)CH\(_2\)CH\(_2\)OH) and does not have this specific structure. Consequently, it gives a negative result (no yellow precipitate)
Source: Myschool Past Questions Archive (Record #58170)
Chemistry
WAEC / WASSCE 2019
Kinetics, Energetics and Equilibrium
If a catalyst is added to a system, the temperature and the pressure remain constant, there would be no effect on the?
A
activation energy of the reaction
B
rate of the reaction
C
rate of the reverse reaction
D
heat of reaction
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #58171)
Chemistry
WAEC / WASSCE 2019
Matter & Separation Techniques
Solution
consider the following reaction equation: 2NH\(_3 \) .+ 3Cl\(_2\) → N2 + 6HCl.
NH\(_3\) is acting as?
A
a reducing agent
B
a dehydrating agent
C
a drying agent
D
an oxidizing agent
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
- As a reducing agent, Ammonia reacts with chlorine to create nitrogen gas and hydrogen chloride vapour in the first step.
Source: Myschool Past Questions Archive (Record #58172)
Chemistry
WAEC / WASSCE 2019
Electrochemistry and Redox
Solution
The oxidation of chromium in Cr\(_2\)O\(_7\)\(^{2-}\) ?
A
+4
B
+5
C
+6
D
+7
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Cr\(_2\)O\(_7\)\(^{2-}\)
Cr\(_2\)O\(_7\) = - 2
Cr\(_2\) + O\(_7\) = - 2
2Cr + 7(-2) = - 2
2Cr - 14 = - 2
2Cr = -2 + 14
2Cr = 12
Cr = \(\frac{12}{2}\)
Cr = + 6
Source: Myschool Past Questions Archive (Record #58174)
Chemistry
WAEC / WASSCE 2019
Acids, Bases, and Salts
The process by which alkanoic acid reacts reversibly with alkanols is known as?
A
saponification
B
esterification
C
carboxylation
D
halogenation
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 #58176)
Chemistry
WAEC / WASSCE 2019
Kinetics, Energetics and Equilibrium
Solution
consider the reaction represented by the following equation: 2SO\(_2\) + O\(_2\) ⇌ 2SO\(_3\)
A decrease in the pressure of the reaction would
A
decrease in the concentration of SO\(_2\)
B
have no effect on the reaction
C
shift the equilibrium position to the left
D
shift the equilibrium position to the right
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
decrease in pressure favors the side with higher volume thus the equilibrium position will shift to the left
Source: Myschool Past Questions Archive (Record #58181)