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.

441.

Which of the following can be obtained by fractional distillation? 

A.

Nitrogen from liquid air

B.

Sodium Chloride from sea water

C.

Iodine from solution of Iodine in carbon tetrachloride

D.

Sulphur from the solution of sulphur in carbon disulphide

Correct answer is A

Fractional distillation is used to separate mixtures into its component parts or fractions with the difference in boiling points between successive fractions must be more than 10°C. An example is the liquid nitrogen and oxygen are then separated by fractional distillation .

442.

The electronic configuration of an element is 1S\(^2\) 2S\(^2\) 2P\(^6\) 3S\(^2\) 3P\(^3\). How many unpaired electrons are there in the element?

A.

5

B.

4

C.

3

D.

2

Correct answer is C

Once you figure out the electron configuration, you fill up the corresponding orbitals with electrons, any left with one is considered unpaired. Since 1s can only hold 2 electrons, and P has 15, that's obviously filled and has no unpaired electrons. The same is for 2s which holds 2, 2p which holds 6, 3s which holds 2.

However 3p can hold 6 electrons and in order for that to be filled up you would need to have an element of 18 electrons. So you fill up as much as you can in 3p by first adding 1 electron to each energy level. 3p has 3 energy levels and there are only 3 electrons left to distribute, so each of those energy levels only gets 1, because you have to fill them all with one before you can start adding a second.

So since you are only able to fill one electron in each of the three energy levels of the 3p orbital, that leaves the orbital open for 1 more electron in each of its energy levels. So there are 3 unpaired electrons in P.

443.

Which of the following factors will speed up the rate of evolution of carbon (iv) oxide in the reaction below?
2HCl + CaCO\(_3\) → CaCl\(_2\) + H\(_2\)O + CO\(_2\)

A.

Increasing the concentration of the acid

B.

Increasing the surface area of CaCO\(_3\)

C.

A and B

D.

Reducing the concentration of the acid

Correct answer is C

The following factors increase a reaction rate
- Increase in concentration of reactants
- Increase in temperature
- Addition of catalyst
- Increase in the surface area of reactant(s)

444.

The part of the total energy of a system that accounts for the useful work done in a system is known as

A.

Enthalpy change

B.

None of the above

C.

Gibb's free energy

D.

Entropy

Correct answer is C

Gibb's free energy is the fraction of the total energy of a system that accounts for how much useful work can be done in a system.

445.

When the end alkyl groups of ethyl ethanoate are interchanged, the compound formed is

A.

propylmethanoate

B.

ethylpropanoate

C.

methyl ethanoate

D.

methyl propanoate

Correct answer is D

No explanation has been provided for this answer.