Page 27 - Q & A STPM 2022 Chemistry

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

Which atomic orbitals overlap to form the carbon-carbon π-bond in ethene,
CH 2 "CH 2 ?
A 2p and 2p
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B 2s and 2p
C sp and sp
2
2
D 2p and sp 2
Answer: A
Only the lateral overlap of two p orbitals will produce a π-bond.
π-bond:
Exam Tips
π bond Exam Tips
σ-Bonds are formed by the overlap of
H H hybridised orbitals. π-Bonds are formed
C C
H H by the overlap of non-hybridised orbitals.
σ bond

14.2 General, Empirical, Molecular and Structural Formulae of Organic
Compounds
Section A Multiple-choice Questions

Question 1
Compound X (molar mass = 54.0 g mol has the following composition by
–1
mass:
C, 89%; H, 11%
What is the molecular formula of X?
A C 9 H 11
B C 2 H 3
C C 4 H 6
D C 4 H 8

Answer: C
Mole ratio of C : H = 89 : 11 = 7.4 : 11 = 1 : 1.5 = 2 : 3
12 1
Let the molecular formula be (C 2 H 3 )n. Term
Relative molecular mass = [2(12) + 3(1)]n
= 54 3
n = 2
\ The molecular formula is C 4 H 6 .

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14 Q&A STPM Chem T3 Layout.indd 343 4/19/19 5:29 PM