Types of formula for organic molecules
5 marks · HardA student investigates three hydrocarbons and records the following information:
| Name | Type of formula | Formula |
|---|---|---|
| methane | displayed | H–C–H (each C bonded to four H) |
| butene | molecular | C4H8 |
| hexane | empirical | CH3 |
Give the molecular formula of methane.
Draw the displayed formula of butene.
Write the molecular formula of hexane.
State the type of formula for 'C4H8'.
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.
Show answer
(a) CH4
(b) Displayed structure showing four carbon atoms in a chain, one double bond, eight hydrogens correctly positioned · must show C–C=C–C skeleton, all hydrogens placed to give 8 total
(c) C6H14
(d) molecular formula
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Molecular formula of methane is CH4.
M1 (b) · 1 mark · Shows four carbon atoms with correct double bond somewhere in the C–C–C–C chain.
A1 (b) · 1 mark · All hydrogens placed for butene (8 hydrogens), showing correct valency.
B2 (c) · 1 mark · Correctly states molecular formula of hexane: C6H14.
B3 (d) · 1 mark · States the type of formula for C4H8 is 'molecular formula'.
Worked solution
a) Methane has one carbon atom bonded to four hydrogens: CH4.
b) The displayed formula for butene (one possible isomer):
c) Hexane's empirical formula is CH3, and it contains 6 carbons and 14 hydrogens, so molecular formula is C6H14.
d) The formula C4H8 shows only the numbers of atoms, so it is a molecular formula.