Past Exam Papers

Question 1

Define the term enthalpy of lattice formation. [2 marks]

Answer 1

The enthalpy change when one mole of a solid ionic compound/lattice is formed from its gaseous ions.

Question 2

A calculation of the enthalpy change of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated in Question 1.2.

Explain this difference. [2 marks]

Answer 2

• AgI contains covalent character/ is not completely ionic
  -so the forces/bonds holding the lattice together are stronger

Question 3

Identify a reagent that could be used to indicate the presence of iodide ions in an aqueous solution and describe the observation made. [2 marks]

Answer 3

-AgNO3
-A yellow coloured precipitate is formed

Question 4

What is the correct expression for Kw? [1 mark]

Answer 4

C - Kw= [H+][OH-]

Question 5

Calculate the pH of pure water at 10ºC. Give your answer to 2 decimal places. [2 marks]

Answer 5

[H+] = √Kw = √2.93*10^-15
[H+] = 5.41 X 10^-8

pH = -log(ans) = 7.27

pH = 7.27

Question 6

Suggest why this pure water at 10ºC is not alkaline.

Answer 6

[H+] = [OH-]

Question 7

Calculate the pH of a 0.0131moldm-3 solution of calcium hydroxide at 10ºC. Give your answer to two decimal places. [3 marks]

Answer 7

[OH-] = 0.0131 X 2 = 0.0262

[H+] = (2.93X10^-15)/0.0262 = 1.118X10^-13

pH = -log(ans) = 12.95

pH = 12.95

Question 8

Predict whether the pH of magnesium hydroxide solution formed at 10ºC is larger than, smaller than or the same as the pH of calcium hydroxide solution at 10ºC.

Explain your answer. [2 marks]

Answer 8

-smaller pH
-magnesium hydroxide is less soluble than calcium hydroxide

Question 9

Write an equation, including state symbols, to show how an atom of titanium is ionised by electron impact and give the m/z value of the ion that would reach the detector first. [2 marks]

Answer 9

Ti(g) -> Ti+(g) + e-

m/z value = 46

Question 10

46 - 9.1
47 - 7.8
48 - 74.6
49 - 8.5

Calculate the relative atomic mass of titanium in this sample. Give your answer to one decimal place. [2 marks]

Answer 10

Ar = (46 X 9.1) + (47 X 7.8) + (48 X 74.6) + (49 X 8.5)

Ar = 4782.5/100 = 47.8

Ar = 47.8

Question 11

Calculate the mass, in kg, of one atom of 49Ti. [1 mark]

Answer 11

49/(6.022 X 10-23)

= (8.136 X 10-23)/ 1000

Mass = 8.14 X 10-26 kg

Question 12

Ke of an ion in the flight tube = 1.01310-13 J
Time of flight of a 49Ti+ ion = 9.81610-7s

Calculate the time of flight of a 47Ti+ ion. Give your answer to the appropriate number of significant figures. [3 marks]

Answer 12

d = t√2E/m

d = (9.816 X 10^-7) √2(1.013 X 10^-13)/(8.14 X 10^-26)

d = 1.55m

t = (1.5468) √(7.504716 X 10^-26)/ 2(1.013 X 10^-13)

t = 9.61 X 10^-7s

Question 13

20.1mol CO and 24.2 mol H2 placed in sealed container. Equilibrium mixture contained 2.16mol methanol.

Calculate the amount, in moles, of carbon monoxide and of hydrogen in the equilibrium mixture. [2 marks]

Answer 13

Start: 20.1, 24.2 , 0

/2.16 (reactants) *2.16 (products)

End: 17.94 , 19.88 , 2.16

Amount of CO = 17.9 mol
Amount of H2 = 19.9 mol

Question 14

Deduce the oxidation states of Nitrogen in NO3- and NO. [2 marks]

Answer 14

NO3- : +5
NO : +2

Question 15

Name the mechanism for Reaction 2 and give an essential condition to ensure that CH3CH2CH2HN2 is the major product. [2 marks]

Answer 15

Nucleophilic substitution and excess NH3

Question 16

Give the IUPAC name of CH3CH2CH2CH2CH(OH)CN. [1 mark]

Answer 16

1-hydroxyhexanenitrile

Question 17

Describe how you would distinguish between separate samples of the two stereoisomers of CH3CH2CH2CH2CH(OH)CN. [2 marks]

Answer 17

• plane of polarised light
• each stereoisomer would rotate the light in opposite directions

Question 18

Explain why the reaction produces a racemic mixture. [3 marks]

Answer 18

• planar carbonyl group
  -can be attacked from either side
• with equal probability

Question 19

Describe how you would distinguish between all four compounds using the minimum number of tests on each compound. [6 marks]

Answer 19

-COOH
- sodium carbonate, effervescence, cloudy limewater
- K and M but not L or N

-OH and -CHO
- acidified potassium dichromate, solution would turn green from yellow
- K, L or N but not M

-CHO
- Fehling’s solution , will go brick red from blue
- N only

-Br
- silver nitrate, cream precipitate formed
- L or N

Question 20

State in general terms what determines the distance travelled by a spot in TLC. [1 mark]

Answer 20

It’s solubility

Question 21

To obtain the chromatogram, the TLC plate was held by the edges and placed in the solvent in the beaker in the fume cupboard. The lid was then replaced in to the beaker. [1 mark]

Answer 21

Ensure the solvent doesn’t touch the pencil line

Question 22

Deduce the relative polarities of 1,2-dinitrobenzene and 1,4-dinitrobenzene and explain why 1,4-dinitrobenzene has the greater Rf value. [2 marks]

Answer 22

Relative polarities: 1,2 is more polar
Explanation: less polar so more attracted to solvent (less soluble) so travels further

Question 23

State two features of the current model that are not shown in the Rutherford model. [2 marks]

Answer 23

• Protons and Neutrons in the nucleus
• There are multiple energy levels that contain electrons

Question 24

Describe the bonding in magnesium. [2 marks]

Answer 24

• metallic bonding is present
• attraction between the lattice of positive metal ions and sea of delocalised electrons

Question 25

Explain, in terms of structure and bonding, why magnesium chloride has a high melting point. [3 marks]

Answer 25

• MgCl2 is a giant ionic lattice
• there are strong electrostatic forces of attraction
• between the oppositely charged Mg2+ and Cl- ions

Question 26

Give one medical use for magnesium hydroxide. [1 mark]

Answer 26

Indigestion relief

Question 27

State, in terms of electrons, the meaning of the term oxidising agent. [1 mark]

Answer 27

An electron acceptor

Question 28

Chlorine has a low boiling point because the forces between the molecules are weak.

Explain how these forces arise between molecules of chlorine. [3 marks]

Answer 28

• there is movement of electrons in one of the molecules
• which induces a dipole in the neighbouring molecule
• and the temporary dipoles created attract

Question 29

State the meaning of the standard enthalpy of combustion. [2 marks]

Answer 29

The enthalpy change when one mole of a substance is completely burnt in oxygen with all substances in their standard states.

Question 30

Explain why there is an attraction between a C=C double bond and Br2. [3 marks]

Answer 30

• Br2 contains an induced dipole and the slight charges causes the molecule to become polarised
• the slight positive charge on one of the Br molecules is attracted to the C=C double bond
• due to the area of high electron density around the double bond

Question 31

Explain why propanone has a lower boiling point than propan-2-ol. [3 marks]

Answer 31

• Propan-2-ol has hydrogen bonding
• Therefore has stronger IM forces compared to the weaker VDW forces of the propanone
• so needs less energy to overcome the bonds in propanone

Question 32

State the benefit to life on earth of ozone in the upper atmosphere. [1 mark]

Answer 32

It absorbs UV, which is harmful

Question 33

Suggest one reason why the use of CFCs was not restricted until several years after Rowland and Molina published their research. [1 mark]

Answer 33

There was an initial lack of evidence to support their research

Question 34

CFC-11 is a greenhouse gas that can contribute to global warming.

State and explain how CFC-11 is able to contribute to global warming. [2 marks]

Answer 34

• the bonds in CFC-11 are able to absorb IF radiation
• due to their polarity
• so the IF radiation gets trapped in the atmosphere

Question 35

Define the term enthalpy change. [1 mark]

Answer 35

The heat energy change at a constant pressure