Past Paper 2019: 1,2 And 3

Question 1

Describe the process of electrospray ionisation and provide an equation for P

Answer 1

Sample dissolved in a volatile solvent, passed through a fine needle at high voltage, gains a proton
P+H—> PH+

Question 2

State the meaning of the term periodicity

Answer 2

The regular and repeating pattern of physical and chemical properties of elements across periods in the periodic table

Question 3

Identify the element in period 4 with the highest electronegativity value

Answer 3

Bromine

Question 4

Identify with element in period 4 with the largest atomic radius and why

Answer 4

Potassium- smallest number of protons/nuclear charge, similar shielding

Question 5

Name the property of arsenic oxide that describes the ability to react in the two different ways

Answer 5

Amphoteric

Question 6

Solid sodium chloride reacts with concentrated sulfuric acid.
Give an equation for this reaction.
State the role of sulfuric acid in this reaction

Answer 6

NaCl2 + H2SO4 —> NaHSO4 + HCl
Role: acid, proton donor

Question 7

Fumes of sulfur dioxide are formed when sodium bromide reacts with conc H2SO4
For this reaction
Give an equation, give other observation, state the role of the sulfuric acid

Answer 7

2NaBr + 2H2SO4 —> Na2SO4 + SO2 + Br2 + 2H2O
Observation- orange/brown fumes/gas
Role:oxidising agent

Question 8

Solution Y contains two different negative ions.
To a sample of solution Y in a test tube a student adds
-silver nitrate solution
-then an excess of dilute nitric acid
-finally an excess of concentrated ammonia solution
The observation:
Silver nitrate- cream precipitate containing compound D and compound E
Excess dilute nitric acid- cream precipitate D and bubbles of gas F
Excess concentrated ammonia solution- colourless solution containing complex ion G
Give the formula of each one and ionic equation for the formation of E.
equation for the conversion of D into G

Answer 8

Formula of D: AgBr
Formula E: Ag2CO3
Formula F:CO2

Ionic for E: 2Ag2+ + CO32- —> Ag2CO3

Conversion of D into G: AgBr + 2NH3 —> Ag(NH3)2+ + Br-

Question 9

Explain how this information (Kp at a higher value) can deduce that the forward reaction is endothermic?

Answer 9

At higher temperature, KP is higher. Equilibrium shifts to the right to oppose increase in temperature

Question 10

In terms of intermolecular forces involved explain the difference in boiling points between ethanol,78 and methoxymethane, -24

Answer 10

Methoxymethan has permenant dipoles between molecules, ethanol has hydrogen bonds between molecules. Hydrogen bonding is the strongest force so will require more energy to overcome the attraction

Question 11

A buffer solution has a constant pH even when diluted , use a mathematical expression to explain this

Answer 11

Ratio [HX/X-]

Question 12

State why cyclohexene can be separated from the aqueous solution using the separating funnel

Answer 12

It is insoluble

Question 13

Give one observation that the student made to confirm that cyclohexene was dry

Answer 13

Liquid goes clear

Question 14

State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electro spray ionisation.

Answer 14

Mass spectrometry does it to more than 1st so have different Mr

Question 15

Explain how carbon dioxide causes global warming

Answer 15

IR emitted from earth can’t escape, transferred to the surroundings through successful collisions

Question 16

Explain why NaBH4 reduces 2-methylbutanal but has no reaction with an Alkenes

Answer 16

Double bond is electron rich- repels nucleophile

Question 17

Describe an experiment to investigate the effect on temperature on the initial rate of this reaction (continuous method with thiosulfate and HCl)

Answer 17

Use disappearing cross technique or colorimetry, put acid or thiosulfate into container with cross, add second reactant and start timing
Repeat at different temperatures , record time taken for cross to disappear, idea of ensuring other variables such as cross and volumes are kept constant. Calculate 1/t and plot rate against T. sketch 2nd order graph