A-Level H2 Chemistry 5

Question 1

Predict the product of the reaction between propan-1-ol and concentrated H₂SO₄ at 170°C.

Accepted Answer

Propene

Answer

At 170°C, concentrated H₂SO₄ dehydrates the alcohol by elimination of water: CH₃CH₂CH₂OH → CH₃CH=CH₂ + H₂O (propene). At 140°C, it would form an ether.

Question 2

What is the difference between SN1 and SN2 mechanisms?

Accepted Answer

SN1 has a carbocation intermediate (two steps); SN2 is one-step with backside attack

Answer

SN1: two-step — carbocation intermediate formed, then nucleophile attacks. SN2: one-step — concerted backside attack by nucleophile, inversion of configuration. SN1 favoured by tertiary; SN2 by primary halides.

Question 3

What is the molecular formula of aspirin (acetylsalicylic acid)?

Accepted Answer

C₉H₈O₄

Answer

Aspirin (acetylsalicylic acid) has the molecular formula C₉H₈O₄. It is formed by the esterification of salicylic acid with ethanoic anhydride.

Question 4

What is shown by a Boltzmann distribution curve in kinetics?

Accepted Answer

The distribution of energies among molecules in a gas at a given temperature

Answer

The Boltzmann distribution shows the spread of molecular kinetic energies in a gas sample at a given temperature. A catalyst or higher temperature shifts the distribution, increasing the proportion of molecules with energy ≥ Ea.

Question 5

What is meant by 'degree of unsaturation' (or index of hydrogen deficiency)?

Accepted Answer

The number of rings and multiple bonds in a molecule compared to the saturated equivalent

Answer

Degree of unsaturation = (2C + 2 + N - H - X)/2 for a molecule. Each ring or double bond contributes 1; each triple bond contributes 2. It helps determine molecular structure.

GCE A-Level Practice Test

GCE A-Level Practice Test

A-Level H2 Chemistry 5