Past Paper 2020: 1,2,3

Question 1

State why there is a difference between the theoretical and experimental value

Answer 1

Has covalent character or partial covalent bonding as well as ionic bonding

Question 2

Explain why the Enthalpy of hydration becomes less exothermic from Li+ to K+

Answer 2

Size of ion increases, charge density decreases, electrostatic attraction between the metal ion and Od- of water decreases

Question 3

Give the meaning of the term relative atomic mass

Answer 3

Average mass of an atom of an element/ 1/12 the mass of one atom of carbon 12

Question 4

Give two reasons why it is necessary to ionise the isotopes of chromium before they can be analysed in the TOF spectrum

Answer 4

1. So they will be accelerated by an electric field towards the negative plate
2. So they can generate a current when hitting the detector

Question 5

Explain why the atomic radius decreases across period 3 from sodium to chlorine

Answer 5

Same shielding, the number of protons increases

Question 6

Identify the element in P3 that has the highest electronegativity

Answer 6

Chlorine

Question 7

Phosphorous burns in air to give phosphorous oxide. Give an equation for this reaction

Answer 7

P4 + 5O2 —> P4O10

Question 8

State the meaning of the term weak acid

Answer 8

Partially dissociates in water to form H+ ions

Question 9

Some reactions of the [Al(H2O)6]3+ are shown

Colourless solution. <————————— [Al(H2O)6]3+ —————> B white precipitate
Containing complex ion A. Na4EDTA I. NaOH. Na2CO3
I
White ppt that reacts to form a colourless solution containing complex ion C

Give the formula of the white ppt B
State one other observation when Na2CO3 is added to a solution containing the 3+ ion, give an equation for this reaction
Give the formula of C and write an equation
Formula of complex ion a

Answer 9

B:
[Al(H2O)3(OH)3]
[Al(H2O)6]3+ + 3CO32- —> 2[Al(H2O)3(OH)3] + 3CO2 + 3H2O
Producing effervescence

C:
[Al(H2O)2(OH)4]-
Excess NaOH
[Al(H2O)3(OH)3] + 4OH- —> [Al(H2O)2(OH)4]- + 4H2O

A: [Al9EDTA)]-

Question 10

Explain with the use of an equation why a solution containing [Al(H2O)6]3+ has a pH <7

Answer 10

[Al(H2O)6]3+ + H2O = [Al(H2O)5(OH)]2+ + H3O+
Al3+ has a small size and a higher charge density- weakens O-H bond, releasing H+

Question 11

State the effect of the addition of a catalyst on the value of Kp

Answer 11

Increase- catalyst does not effect the position of the equilibrium

Question 12

Explain why the melting points of these two compounds are different- XeF4 and PF3 by referencing their shapes

Answer 12

XeF4 has 4Bonding pairs and 2 lone pairs around xe
PF3 has 3 bonding pairs and 1 lone pair around P
XeF4 is square planar
PF3 is pyramidal
Electron pairs repel as far as possible
The relative strength of the intermolecular forces in XeF4, XeF4 has vander waal forces and PF3 has dipole dipole forces. Stronger intermolecular forces in XeF4 due to larger Mr or more electrons or larger molecules or packs more closely together.

Question 13

State when is observed when silver nitrate solution is added to sodium fluoride

Answer 13

No precipitate formed

Question 14

State what is observed when silver nitrate solution is added to sodium fluoride solution

Answer 14

White fumes
NACl + H2SO4 —> NaHSO4 + HCl
Acts as a base

Question 15

Give an equation for the redox reaction between solid sodium bromide and concentrated sulfuric acid
Explain using oxidation states, why this is a redox reaction

Answer 15

2NaBr + 2H2SO4 —> Na2SO4 + Br2 + SO2 + 2H2O
Br changes from -1 to O so it becomes oxidised
S changes state from +6-+4 so is reduced

Question 16

State what is observed when aqueous chlorine is added to sodium bromide solution
Give an ionic equation for the reaction

Answer 16

Brown/orange solution
Cl2 + 2Br- —> 2Cl- + Br2

Question 17

Define the term overall order of reaction

Answer 17

The sum of powers/indices to which concentrations are raised in the rate equation

Question 18

Suggest a simple way to detect if Ethanolic acid has reacted

Answer 18

Producers a sweet smell

Question 19

Describe how infrared spectra can be used to distinguish between isomers

Answer 19

Each isomer will have a unique fingerprint region below 1500- compare to a known date base

Question 20

Suggest two ways in which the melting point of the crude aspirin collected would differ from the melting point of pure aspirin

Answer 20

Value will be lower
Range of values will be differnt

Question 21

Describe two important precautions when heating the mixture of ethanol and crude aspirin

Answer 21

Ethanol is flammable so use water bath to heat
Heat temperature to below boiling point so ethanol does not boil away

Question 22

A small amount of cold ethanol is then poured through the Büchner funnel
Explain the purpose of this

Answer 22

To remove any soluble impurities

Question 23

Describe one difference you would expect to see between crude and purified aspirin

Answer 23

Pure product will have larger crystals and will be shinier

Question 24

Define the term electronegativity
Explain the polarity of the C-Br bond in 2-bromopropane

Answer 24

The relative ability of an atom to attract a pair of electrons in a covalent bond
Br is more electronegative than C
So Br is d- and C is d+

Question 25

When an excess of water is added to ethanol a similar Nucleophilic addition reaction occurs. Suggest why this reaction is slower that the reaction in part with chloroethanl

Answer 25

C in C=O is less d+ because CH3 attached is donating an electron so there is a higher activation energy