PAPER 3 2020

Question 1

Explain how oxides of nitrogen are formed in engines (2 marks)

Answer 1

• nitrogen and oxygen react in air
• at high temperatures

Question 2

Why is it desirable to decrease emissions of oxides of nitrogen from vehicles (1 mark)

Answer 2

• formation of acid rain
• causes respiratory problems

Question 3

State the meaning of the term heterogenous catalyst (2 marks)

Answer 3

• catalyst in different phase from reactants
• speeds up reaction without being used up

Question 4

1. State why sodium oxide and magnesium oxide both form alkaline solutions in water
2. Suggest why sodium oxide forms a solution with a higher pH than the solution formed from magnesium oxide

Answer 4

1. Oxide ions react with water to form hydroxide (OH-) ions
2. Sodium oxide more soluble than magnesium oxide

Question 5

Give an equation for the reaction between phosphorus (V) oxide and water

Answer 5

P4O10 + 6H20 —> 4H3PO4

Phosphorus oxide + water —-> phosphoric acid

Question 6

In the contact process, sulfur (IV) oxide is converted into sulfur (VI) oxide using vanadium (V) oxide as a catalyst.

Give 2 equations to show how the vanadium oxide acts as a catalyst in this process.

Answer 6

V2O5 + SO2 —> V2O4 + SO3

V2O4 + 1/2 O2 —> V2O5

Question 7

Explain why complexes formed from transition metal ions are coloured (3 marks)

Answer 7

• absorb (some) wavelengths of (visible) light
• to excite electrons in d-orbitals
• remaining wavelengths of light are reflected/transmitted (to give colour seen)

Question 8

Why is zinc not classed as a transition metal

Answer 8

It doesnt have an atom or stable ion with a partially filled d shell.

(Doesn’t form coloured ions)

Question 9

nm to m conversion

Answer 9

1 nm x 10^-9 = 1m

Question 10

Describe how a calibration graph is produced to find an unknown concentration

Answer 10

• measure absorbance for known concentrations
• plot graph for absorbance v concentration
• read value of concentration for measured absorbance from graph

Question 11

Cisplatin works by causing the death of rapidly dividing cells.

Name the process that is prevented by cisplatin during cell division.

Answer 11

DNA replication

Question 12

Graphs for 0 order, 1st order, and order greater than 1

Question 13

Activation energy equation linked to gradient

Answer 13

Ea = gradient x R (gas constant)

Question 14

State the substances and conditions needed in a standard hydrogen electrode (3 marks)

Answer 14

• H2 (g) and 100kPa
• Pt electrode and 298K
• 1 mol dm-3 and HCl/H+

Question 15

Use the data to explain why copper does not react with most acids but does react with nitric acid.

Answer 15

+0.34 shows Cu less powerful reducing agent than H2

+0.96 compared with 0.34 shows the EMF for reaction of Cu with nitric acid is positive