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Chemistry
WAEC / WASSCE 2023
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
The pair of compounds that belongs to the same homologous series is
A
\(C_2H_6\) and \(C_4H_{10}\)
B
\(C_3H_8\) and \(C_3H_6\)
C
\(C_2H_4\) and \(C_4H_{10}\)
D
\(C_4H_{10}\) and \(C_5H_{10}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
In the given options, \(C_2H_6\) (ethane) and \(C_4H_{10}\) (butane) both belong to the same homologous series, as they have the same alkane functional group \(C_nH_{2n}+2\) and differ by a \(CH_2\) group:
\(C_2H_6\): Ethane
\(C_4H_{10}\): Butane
Both of these compounds are members of the alkane homologous series.
Source: Myschool Past Questions Archive (Record #69509)
Chemistry
WAEC / WASSCE 2023
Oxidation, Reduction & Redox Reactions
Solution
Which of the following equations does not illustrate correctly one of the reactions of chlorine?
A
\(Ca(OH)_2 + Cl_2 → CaOCl_2 + H_2O\)
B
\(Cl_2 + 2NaF → 2NaCl + F_2\)
C
\(Cl_2 + 2NaOH → NaCl + NaClO + H_2O\)
D
\(H_2S + Cl_2 → 2HCl + S\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The equation \(Cl_2 + 2NaF → 2NaCl + F_2\) does not illustrate correctly one of the reactions of chlorine.
In this reaction, chlorine reacts with sodium fluoride to form sodium chloride and fluorine gas. However, this reaction is not possible because fluorine is a much more reactive element than chlorine. When chlorine and fluorine react, they form a compound called chlorine trifluoride (\(ClF_3)\), which is a very powerful oxidizing agent.
Source: Myschool Past Questions Archive (Record #69510)
Chemistry
WAEC / WASSCE 2023
Acids, Bases, pH & Salts
Solution
The salt solution formed firm a reaction between ethanoic acid and sodium hydroxide solution would be
A
amphoteric.
B
neutral
C
basic
D
acidic
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Ethanoic acid is a weak acid, while sodium hydroxide is a strong base. When these two substances react, they neutralize each other, forming salt and water. The salt is a compound of the cation from the base and the anion from the acid. In this case, the salt is sodium ethanoate, which is a basic salt.
Source: Myschool Past Questions Archive (Record #69511)
Chemistry
WAEC / WASSCE 2023
Nature of Matter & Separation Techniques
Solution
The separation technique that is suitable for separating iodine from tetrachloromethane is
A
solvent extraction
B
decantation
C
fractional distillation
D
filtration
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Solvent extraction, also known as liquid-liquid extraction, is a technique used to separate substances based on their differential solubilities in two immiscible liquids. In this case, since iodine and tetrachloromethane have different solubilities in certain solvents, you can use solvent extraction to selectively dissolve one of the substances while leaving the other behind. Iodine is a non-polar molecule, while tetrachloromethane is a polar molecule. This means that iodine will dissolve in a non-polar solvent, while tetrachloromethane will dissolve in a polar solvent
Source: Myschool Past Questions Archive (Record #69512)
Chemistry
WAEC / WASSCE 2023
Chemical Energetics & Thermochemistry
Solution
Consider the following reaction equation:
\(2SO_3(g) → 2SO_2(g) + O_2\)(g)
∆H = +198 kJ/mol
Which of the following statements about the reaction is correct?
A
198 kJ of energy is given off
B
The reaction is exothermic
C
The reaction container would feel warm.
D
198 kJ of energy is absorbed
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
A positive value of ∆H (+198 kJ mol^-1) indicates that the reaction is endothermic, meaning it requires an input of energy to proceed. In this case, the reaction absorbs 198 kJ of energy per mole of reactants to convert 2 moles of \(SO_3\) into 2 moles of \(SO_2\) and 1 mole of \(O_2\). This means that the reaction container would need to be supplied with energy, and it would feel cooler rather than warmer.
Source: Myschool Past Questions Archive (Record #69513)
Chemistry
WAEC / WASSCE 2023
Chemical Bonding & Intermolecular Forces
Solution
Arrange the following compounds in decreasing order of their boiling points: \(NH_3\), HF, \(SiH_4\), \(CH_4\)
A
HF,\(NH_3\), \(SiH_4\), \(CH_4\)
B
\(CH_4\), \(SiH_4\), HF, \(NH_3\),
C
\(NH_3\),\(CH_4\), \(SiH_4\), HF
D
\(CH_4\), \(SiH_4\), \(NH_3\), HF
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
The correct order of boiling points of the compounds \(NH_3\), HF, \(SiH_4\), and \(CH_4\) is HF, \(NH_3\), \(SiH_4\), \(CH_4\).
The correct order of boiling points of the compounds \(NH_3\), HF, \(SiH_4\), and \(CH_4\) is HF, \(NH_3\), \(SiH_4\), \(CH_4\).
The boiling point of a compound is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. The stronger the intermolecular forces, the higher the boiling point.
Source: Myschool Past Questions Archive (Record #69514)
Chemistry
WAEC / WASSCE 2023
Atomic Structure, Orbitals & Nuclear Chemistry
Solution
Copper (II) ions are able to participate in co-ordinate covalent bonding because they
A
are coloured
B
are positively charged
C
have vacant d-orbital
D
have unpaired electrons
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Copper (II) ions have vacant d-orbitals. This means that they can accept a pair of electrons from a donor atom. When a copper (II) ion accepts a pair of electrons, it forms a co-ordinate covalent bond with the donor atom.
Source: Myschool Past Questions Archive (Record #69515)
Chemistry
WAEC / WASSCE 2023
Electrolysis & Electrochemical Cells
Solution
What takes place at the cathode during electrolysis?
A
Anions lose electrons
B
Anions are oxidized
C
Cations are oxidized
D
Cations are discharged.
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Cations are discharged at the cathode during electrolysis.
Electrolysis is the process of using an electric current to cause a chemical reaction to take place. The cathode is the negative electrode in an electrolytic cell. It is where cations (positively charged ions) are discharged
Source: Myschool Past Questions Archive (Record #69516)
Chemistry
WAEC / WASSCE 2023
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Carbon is deposited in the exhaust pipes of cars because of
A
presence of additives in petrol
B
incomplete combustion of petrol
C
presence of carbon in petrol
D
contamination of petrol with diesel
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Carbon is deposited in the exhaust pipes of cars primarily because of incomplete combustion of petrol. When the fuel (petrol) is burned in the engine's combustion chamber, ideally, it should be fully oxidized, resulting in the production of carbon dioxide (CO2) and water vapor. However, in real-world conditions, the combustion process may not be perfect, and some of the carbon in the petrol may not fully burn. As a result, carbon particles are formed and get carried through the exhaust system.
Source: Myschool Past Questions Archive (Record #69517)
Chemistry
WAEC / WASSCE 2023
Kinetic Theory of Matter & Gas Laws
Solution
Which of the following laws or theory cannot be explained by the application of the kinetic theory of gases?
A
Dalton's atomic theory
B
Charle's law
C
Boyle's law
D
Gay- Lussac's law
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Dalton's atomic theory cannot be explained by the application of the kinetic theory of gases because it deals with the atomic-level structure and behavior of matter, which is beyond the scope of the kinetic theory's focus on the macroscopic behavior of gas particles. The other laws (Charles' law, Gay-Lussac's law, and Boyle's law) can be well understood and explained by the kinetic theory of gases, as they relate to the macroscopic properties and behaviors of gases and their constituent particles.
Source: Myschool Past Questions Archive (Record #69518)
Chemistry
WAEC / WASSCE 2023
Atomic Structure, Orbitals & Nuclear Chemistry
Solution
How many unpaired electrons are present in \(_{26}Fe^{3+}\)?
A
4
B
2
C
3
D
5
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
There are 5 unpaired electrons present in \(_{26}Fe^{3+}\).
The atomic number of iron is 26, so it has 26 electrons. When iron loses 3 electrons to form \(Fe^{3+}\), it loses 2 from the s orbital and 1 from the d orbital. This leaves 5 unpaired electrons in the d orbital.
The electron configuration of \(Fe^{3+}\) is [Ar]3d5. The 5 d electrons are all unpaired because Hund's rule states that electrons will occupy degenerate orbitals singly before they pair up. This is because unpaired electrons have a lower energy than paired electrons.
Source: Myschool Past Questions Archive (Record #69519)
Chemistry
WAEC / WASSCE 2023
Air & Environmental Chemistry
Solution
A consequence of global warming is
A
air pollution
B
High Humidity
C
flooding
D
Water pollution
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Flooding is a major consequence of global warming because as the Earth's ice caps and glaciers melt, sea levels rise. This can cause flooding in coastal areas and low-lying islands. For example, in 2019, the Netherlands experienced its worst flooding in decades, with over 10,000 homes damaged and thousands of people evacuated.
Source: Myschool Past Questions Archive (Record #69520)
Chemistry
WAEC / WASSCE 2023
Periodic Table & Periodicity
Solution
Going down group II in the periodic table normally
A
ionization energy increases
B
melting point increases
C
shielding effect decreases
D
electronegativity increases
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Melting point increases. This is because the atoms become larger as you go down the group, which means that the metallic bonds between them become stronger.
Source: Myschool Past Questions Archive (Record #69521)
Chemistry
WAEC / WASSCE 2023
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
The primary component of natural gas
A
ethane
B
methane
C
butane
D
propane
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Natural gas is a fossil fuel primarily composed of hydrocarbon gases. The primary component of natural gas is methane, which typically makes up a significant portion of the gas mixture. Methane is a simple hydrocarbon with one carbon atom and four hydrogen atoms (CH4). It is the main component of natural gas, often accounting for over 90% of its composition.
Source: Myschool Past Questions Archive (Record #69522)
Chemistry
WAEC / WASSCE 2023
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
The gas that is less dense than air is
A
nitrogen
B
chlorine
C
Carbon(IV) oxide
D
Oxygen
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
The density of a gas is directly proportional to its molar mass. This means that gases with a lower molar mass will be less dense than gases with a higher molar mass. Nitrogen (N2) has a molar mass of 28 g/mol, which is less than that of air (approximately 29 g/mol), making it less dense than air.
Source: Myschool Past Questions Archive (Record #69523)