Paper 2 Pre-Release Material 2018

Question 1

What does the fact that Napolean died 6 years after his exile suggest?

Answer 1

He had a slow death and probably wasn’t deliberately poisoned

Question 2

What is the most common Arsenic ion?

Which subshell are electrons lost from?

Answer 2

As³⁺

Lost from p subshell

Question 3

Draw the structure of elemental arsenic

What type of bonding does it display?

Answer 3

Metallically bonded to itself

NOTE: Metal atoms should have +3 charge

Question 4

What is the chemical formula of arsenic sulphate?

Answer 4

As₂(SO₄)₃

Question 5

What is the chemical formula of arsenic trisulphide?

Answer 5

As₂S₃

Question 6

What is white arsenic also known as?

What is its chemical formula?

Answer 6

Arsenic (tri)oxide

As₂O₃

(Same formula as arsenic trisulphide except with O)

Question 7

Draw the structure of arsenic oxide

What type of bonding does it display?

Answer 7

Covalent bonding

Question 8

Write out the half equations + overall equation for the electrolysis of arsenic oxide

Answer 8

As³⁺_(l) + 3e^- → As_{<strong>(s</strong>)} Reduction

2O^2-_(l) → O_2(g) + 4e^{<strong>- </strong>} Oxidation

Overall equation: 4As³⁺_(l) + 6O^2-_(l) → 4As_(s) + 3O_2(g)

(Reactants could also be written as 2As₂O_3(l))

Question 9

What is the primary structure of a protein?

Answer 9

The linear order of amino acids in the chain

Question 10

What is the secondary structure of a protien?

Answer 10

Alpha helicies and beta-pleated sheets

Hydrogen bonds form between chains

Question 11

What is the tertiary structure of a protein?

Answer 11

The folding between protein chains

Caused by a range of different interactions e.g. disulphide bridges

Question 12

What is competitive inhibition?

Describe the process

Answer 12

When a molecule with a similar shape to the substrate binds strongly to the active site

This means the usual substrate cannot bind/enter and the usual reaction doesn’t occur

Question 13

What is an active site?

Answer 13

A cleft in an enzyme surface where substrate molecules can bind + react

Part of the tertiary stucture - exactly matches the structure of the substrate

Question 14

What is does it mean for an enzyme to be denatured?

Answer 14

When the active site of the enzyme changes due to changes in pH or increased temp.

Denaturing means the substrate no longer fits the active site so reactions can no longer occur

Question 15

What determines the shape of the active site?

Answer 15

Depends on the tertiary structure of the protein that makes up the protein

The tertiary structure is determined by the interactions betwen the amino acid side groups, e.g. h-bonding, ionic bonds, + disulphide bonds

Question 16

What was the initial/first test to detect Arsenic?

(Give the equation)

Answer 16

As₂O_3(s) + 3H₂S_(aq) → AsS_3(s) + 3H₂O_(l)

Yellow precipitate of Arsenic sulphide formed however dissolves over time

Question 17

What is the shape + bond angle of H₂S?

What molecule is it similar to (in this regard)?

Answer 17

104.5º, Bent

Same as water

Question 18

What is the equation for the Marsh test?

What type of reaction occurs?

How did it show the presence of arsenic?

Answer 18

Zinc metal + H₂SO₄ used. Arsenic converted into arsine gas which is heated + decomposes:

2AsH_3(g) → 2As_(s) + 3H_2(g)

Thermal decomposition

Silvery-black arsenic metal deposited as film on sides of test tube

Question 19

Describe how x-ray fluorescent spectroscopy is used to test for arsenic

Answer 19

High energy radiation (x-ray) hits an atom – it can eject an electron from
an inner electron shell.

An electron from the next outer shell can then descend to fill the
gap

When the electron descends it will emit an X-Ray ΔE = hν

This energy difference has a characteristic value for each type of
atom

(Due to the fact that each has unique electron config + energy levels discrete/quantised)

Question 20

Was is the formula for Scheele’s green?

What are the oxidation states?

Answer 20

CuAsHO₃

Cu = +2
As = +3
H = +1
O = -2 (x3 = -6)

Question 21

Why is Scheele’s green coloured?

Answer 21

The d-orbital splits when a ligand complexes to the central metal ion.

The complimentary colour is absorbed (red) and green is reflected. This
is the colour we see

Question 22

What compouds does Scheele’s green form when it becomes damp + mouldy?

Answer 22

Arsine

Dimethyl arsine

Trimethyl arsine

(they all have the same structure as the pic but with a different no. methyl groups. Arsine has none + has Hs instead)

Question 23

What are the advantages + disadvantages of the initial test for arsenic?

Answer 23

Involves simple test tube chemisty

BUT

Yellow precipitate of arsenic sulphide breaks down quickly

Question 24

What are the advantages + disadvantages of the Marsh test for arsenic?

Answer 24

Tube can be sealed + used as evidence

Very specific - virtually no other element behaves this way

Can use/detect very small amounts of arsenic

BUT

Destructive test

Hazardous test (arsine gas)

Not sensitive enough to detect As in hair

Question 25

What are the advantages + disadvantages of using X-ray fluorscence spectroscopy to test for arsenic?

Answer 25

Non-destructive

Can detect extremely minute quanities - smallest of all tests

Gives unique characteristic peaks for atoms - more specific than Marsh Test

BUT

Requires specialised, expensive equipment

Question 26

What are the 3 oxides of arsenic?

Answer 26

Arsenic dioxide - AsO₂

Arsenic trioxide - As₂O₃

Arsenic pentoxide - As₂O₅

Question 27

Which element’s oxides are the structures of arsenic tri- + pentoxide similar to?

Answer 27

Phosphorous tri- + pentoxide

Question 28

What are the most common oxidation states of arsenic?

What compounds are they found in?

Answer 28

+3 in arsenites (probs most likely to be in exam)

-3 in arsenides

+5 in arsenates - most common oxidation state in organic molecules