Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

26.

How many unpaired electrons are present in \(_{26}Fe^{3+}\)?

A.

4

B.

2

C.

3

D.

5

Correct answer is D

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.

27.

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

Correct answer is A

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.

28.

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

Correct answer is B

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.

29.

What takes place at the cathode during electrolysis?

A.

Anions lose electrons

B.

Anions are oxidized

C.

Cations are oxidized

D.

Cations are discharged.

Correct answer is D

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

30.

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

Correct answer is C

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.