Displayed formulae
4 marks · NormalThe displayed formula below represents a simple alkene:
Identify the name of this alkene.
Explain how you used the displayed formula to identify the molecule.
State the total number of hydrogen atoms in this molecule.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Propene
(b) Counted three carbon atoms in a chain with a double bond between the first two; all other bonds are single and hydrogens fill to give 4 bonds per carbon. This matches the structure of propene.
(c) 6
Also accept: Propene, C3H6
Common mistakes: Counting wrong number of hydrogens; Confusing alkane/alkene
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly names the alkene as propene.
M1 (b) · 1 mark · Use of number of carbons and double bond in the structure to identify the molecule.
A1 (b) · 1 mark · Notes all carbons have four bonds, hydrogens fill the rest.
B2 (c) · 1 mark · States the molecule has 6 hydrogen atoms.
Worked solution
a) The structure shows 3 carbon atoms in a chain with a double bond between the first two. This is propene.
b) Identified as propene by counting carbon atoms and observing a C=C double bond at the start of the chain. Hydrogens are added until each carbon has four bonds.
c) There are 6 hydrogens attached (two to C1, one to C2, and three to C3).