Question

=C6H5 -Ċ-Ċ I-0-I H n

1-Calculate the molecular weight of the repeat unit (monomer) for polystyrene (above) (2 marks)

2-Using the table below, calculate the degree of polymerisation for polystyrene

Molecular weight range (g/mol)		Number fraction,xi
500-1000		0.02
1000-3000		0.13
3000-5000		0.25
5000-10000		0.41
10000-25000		0.15
25000-50000		0.04

3-Which crystal type would be expected for Nickel Oxide (NiO, Ni²⁺ ionic radius = 0.069nm, O^2- ionic radius = 0.14nm) (2 marks)

4-In order to save weight, a composite component is to be made of aligned fibreglass and Epoxy resin to replace an aluminium component. The moduli of the fibreglass and epoxy are 85 GPa and 2.4 GPa respectively. Calculate the fraction of fibreglass and Epoxy resin in the composite so that the longitudinal modulus of the composite replicates the modulus of aluminium (69 GPa)

5-For the composite calculated in the previous question, what is the transverse modulus

6-Briefly describe the mechanisms/reasons for the following phenomena (1-2 sentences each)

Polypropylene is a thermal insulator

Gold is an electrical conductor

Boron doped Silicon is an electrical semiconductor

Answer 1

The repeating unit is CH₂.

The molar mass of C is 12 g/mol.

The molar mass of H is 1 g/mol.

There are total 8 carbons and 8 hydrogens in the given compound.

The total molecular weight of the polystyrene is (12*8+1*8)=104 g/mol

The molecular weight of the repeating unit (CH₂) is 14 g/mol.