Page 38 - Q & A STPM 2022 Chemistry

Chemistry Term 3 STPM Chapter 14 Introduction to Organic Chemistry
Question 2

Arrange the following alcohols in the order of decreasing boiling point.
CH 3 CHCH 3 ; CH 3 CH 2 CH 2 OH; HOCH 2 CH 2 OH
&
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
OH
I II III
A I, II, III
B I, III, II
C II, I, III
D III, II, I

Answer: D
Generally, diols have higher boiling points than monohydric alcohols because
they can form more hydrogen bonding.
II is linear but I is branching. Branching decreases the strength of the van der
Waals force between the molecules.

Question 3
The table below lists the boiling point of some haloalkanes.

Compound C 2 H 5 Cl C 2 H 5 Br C 2 H 5 I
Boiling point/°C 12 37 73

Which statement explains the difference in their boiling points?
A The strength of the hydrogen bond increases in the order C 2 H 5 Cl, C 2 H 5 Br,
C 2H 5I.
B The strength of the carbon-halogen bond decreases in the order C 2 H 5 Cl,
C 2 H 5 Br, C 2 H 5 I.
C The size of the molecule increases in the order C 2 H 5 Cl, C 2 H 5 Br, C 2 H 5 I.
D The polarity of the carbon-halogen bond increases in the order C 2 H 5 Cl,
C 2 H 5 Br, C 2 H 5 I.

Answer: C
Exam Tips
Exam Tips
Boiling point depends on the strength of the intermolecular forces only.
Term
3 The strength of the van der Waals force increases with the size of the molecule.
Haloalkanes cannot form hydrogen bonds.

354

14 Q&A STPM Chem T3 Layout.indd 354 4/19/19 5:29 PM