4.1.2 Alkanes

Question 1

Describe the shape and bond angle of an alkane molecule

Answer 1

Tetrahedral shape around each carbon with a bond angle of 109.5

Question 2

Explain the shape of an alkane molecule

Answer 2

Each carbon has four bonded pairs of electrons each repelling each other equally forming a tetrahedral shape around each carbon

Question 3

Explain how boiling point changes as carbon chain length increases

Answer 3

Boiling point increases with chain length
More induced dipole dipole interactions
More energy required to overcome

Question 4

Explain how boiling point changes as branching increases

Answer 4

Lower boiling point
Fewer dipole - dipole interactions as less closely packed together as reduced surface contact

Question 5

Describe the reactivity of alkanes

Answer 5

Low reactivity as high bond enthalpiesand very low polarity between sigma bonds

Question 6

Define homolytic fission

Answer 6

Breaking of covalent bond evenly where each bonded atom receives one electron from the bonded pair

Question 7

Define heterolytic fission

Answer 7

Uneven breaking of covalent bond where one bonded atoms from the bonded pair receives both electrons

Question 8

What is a limitation of free radical substitution

Answer 8

Formation of a mixture of organic products due to further substitution

Question 9

Organic compound E is formed by substitution of some H atoms in butane by Cl atoms
A chemist found that 0.636g of compound E had a volume of 78cm-1. Under conditions used molar gas volume was 32.5 dm3 mol-1
Determine the molecular formula of compound E

Answer 9

Moles of E = 78/32500 = 2.4 x 10-3
Mr of E = 0.636/ 2.4 x 10-3 = 256 g mol -1
Molecular formula = C4H4Cl6