Paper 2 Pre-Release Material 2018 Flashcards Preview

A Level Chemistry (OCR B Salters) > Paper 2 Pre-Release Material 2018 > Flashcards

Flashcards in Paper 2 Pre-Release Material 2018 Deck (28):
1

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

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

2

What is the most common Arsenic ion?

Which subshell are electrons lost from?

As3+

Lost from p subshell

3

Draw the structure of elemental arsenic

What type of bonding does it display?

Metallically bonded to itself

 

NOTE: Metal atoms should have +3 charge

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4

What is the chemical formula of arsenic sulphate?

As2(SO4)3

5

What is the chemical formula of arsenic trisulphide?

As2S3

6

What is white arsenic also known as?

What is its chemical formula?

Arsenic (tri)oxide

As2O3

 

(Same formula as arsenic trisulphide except with O)

7

Draw the structure of arsenic oxide

What type of bonding does it display?

Covalent bonding

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8

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

As3+(l) + 3e- → As(sReduction

2O2-(l) → O2(g) + 4e Oxidation

Overall equation: 4As3+(l) + 6O2-(l) → 4As(s) + 3O2(g)

 

(Reactants could also be written as 2As2O3(l))

9

What is the primary structure of a protein?

The linear order of amino acids in the chain

10

What is the secondary structure of a protien?

Alpha helicies and beta-pleated sheets

Hydrogen bonds form between chains

11

What is the tertiary structure of a protein?

The folding between protein chains

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

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12

What is competitive inhibition?

Describe the process

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

13

What is an active site?

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

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

14

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

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

15

What determines the shape of the active site?

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

16

What was the initial/first test to detect Arsenic?

(Give the equation)

As2O3(s) + 3H2S(aq) → AsS3(s) + 3H2O(l)

Yellow precipitate of Arsenic sulphide formed however dissolves over time

17

What is the shape + bond angle of H2S?

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

104.5º, Bent

Same as water

18

What is the equation for the Marsh test?

What type of reaction occurs?

How did it show the presence of arsenic?

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

2AsH3(g) → 2As(s) + 3H2(g)

Thermal decomposition

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

19

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

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)

20

Was is the formula for Scheele's green?

What are the oxidation states?

CuAsHO3

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

21

Why is Scheele's green coloured?

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

22

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

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)

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23

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

Involves simple test tube chemisty

BUT

Yellow precipitate of arsenic sulphide breaks down quickly

24

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

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

25

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

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

26

What are the 3 oxides of arsenic?

Arsenic dioxide - AsO2

Arsenic trioxide - As2O3

Arsenic pentoxide - As2O5

27

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

Phosphorous tri- + pentoxide

28

What are the most common oxidation states of arsenic?

What compounds are they found in?

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

-3 in arsenides

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