Home / AS & A Level Chemistry 13.1 Formulae, functional groups and the naming of organic compounds Exam Style Practice Questions Paper 1

AS & A Level Chemistry 13.1 Formulae, functional groups and the naming of organic compounds Exam Style Practice Questions Paper 1- New Syllabus

A Level Chemistry Paper 1 - All Chapters

Question

The diagram shows the skeletal formula of the hormone testosterone.

What is the molecular formula of testosterone?

(A) \(\mathrm{C_{19}H_{28}O_2}\)
(B) \(\mathrm{C_{17}H_{22}O_2}\)
(C) \(\mathrm{C_{17}H_{24}O_2}\)
(D) \(\mathrm{C_{19}H_{26}O_2}\)
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathrm{A}} \)

From the skeletal formula:

  • There are 19 carbon atoms.
  • There are 2 oxygen atoms (one ketone group and one alcohol group).
  • Accounting for the four fused rings and the double bond gives a total of 28 hydrogen atoms.

Therefore, the molecular formula is:

\(\mathrm{C_{19}H_{28}O_2}\)

Therefore, the correct answer is (A).

Question 

An organic compound, T, contains only one functional group.

Compound T has the empirical formula \( \mathrm{C_2H_4O} \).

Some functional groups are listed.

1.  Alcohol
2.  Aldehyde
3.  Ester
4.  Ketone

Which functional groups are possible for compound T?

(A) 1 and 3
(B) 1 and 4
(C) 2 and 3
(D) 2 and 4
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathrm{C}} \)

The empirical formula is \( \mathrm{C_2H_4O} \), so any possible molecular formula must be a whole-number multiple of this ratio.

  • Aldehydes can have the formula \( \mathrm{C_nH_{2n}O} \), for example ethanal, \( \mathrm{C_2H_4O} \).
  • Esters can also have molecular formulas that simplify to \( \mathrm{C_2H_4O} \), for example compounds with formula \( \mathrm{C_4H_8O_2} \).
  • Alcohols have the general formula \( \mathrm{C_nH_{2n+2}O} \), which does not simplify to \( \mathrm{C_2H_4O} \).
  • Ketones require at least three carbon atoms, so no ketone has the empirical formula \( \mathrm{C_2H_4O} \).

Therefore, the possible functional groups are 2 and 3, so the correct answer is (C).

Question 

Each mineral listed behaves as a mixture of two carbonate compounds. They can be used as fire retardants because they decompose on heating, producing \( \mathrm{CO_2} \). This gas smothers the fire.

Barytocalcite, \( \mathrm{BaCa(CO_3)_2} \)
Dolomite, \( \mathrm{CaMg(CO_3)_2} \)
Huntite, \( \mathrm{Mg_3Ca(CO_3)_4} \)

What is the order of effectiveness as fire retardants, from best to worst?

 Best→Worst
(A)DolomiteBarytocalciteHuntite
(B)DolomiteHuntiteBarytocalcite
(C)HuntiteBarytocalciteDolomite
(D)HuntiteDolomiteBarytocalcite
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathrm{D}} \)

The effectiveness of the minerals depends on the amount of \( \mathrm{CO_2} \) released when their carbonate ions decompose.

Each carbonate ion produces one mole of \( \mathrm{CO_2} \).

Number of carbonate ions per formula unit:

Barytocalcite: \(2\)
Dolomite: \(2\)
Huntite: \(4\)

Huntite releases the greatest amount of \( \mathrm{CO_2} \), making it the most effective fire retardant.

Between dolomite and barytocalcite, magnesium carbonate decomposes more readily than barium carbonate, so dolomite releases \( \mathrm{CO_2} \) more easily than barytocalcite.

Therefore, the order from best to worst is Huntite → Dolomite → Barytocalcite. Hence, the correct answer is (D).

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