What does the fact that Napolean died 6 years after his exile suggest?
He had a slow death and probably wasn't deliberately poisoned
What is the most common Arsenic ion?
Which subshell are electrons lost from?
Lost from p subshell
Draw the structure of elemental arsenic
What type of bonding does it display?
Metallically bonded to itself
NOTE: Metal atoms should have +3 charge
What is the chemical formula of arsenic sulphate?
What is the chemical formula of arsenic trisulphide?
What is white arsenic also known as?
What is its chemical formula?
(Same formula as arsenic trisulphide except with O)
Draw the structure of arsenic oxide
What type of bonding does it display?
Write out the half equations + overall equation for the electrolysis of arsenic oxide
As3+(l) + 3e- → As(s) Reduction
2O2-(l) → O2(g) + 4e- Oxidation
Overall equation: 4As3+(l) + 6O2-(l) → 4As(s) + 3O2(g)
(Reactants could also be written as 2As2O3(l))
What is the primary structure of a protein?
The linear order of amino acids in the chain
What is the secondary structure of a protien?
Alpha helicies and beta-pleated sheets
Hydrogen bonds form between chains
What is the tertiary structure of a protein?
The folding between protein chains
Caused by a range of different interactions e.g. disulphide bridges
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
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
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
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
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
What is the shape + bond angle of H2S?
What molecule is it similar to (in this regard)?
Same as water
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)
Silvery-black arsenic metal deposited as film on sides of test tube
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
When the electron descends it will emit an X-Ray ΔE = hν
This energy difference has a characteristic value for each type of
(Due to the fact that each has unique electron config + energy levels discrete/quantised)
Was is the formula for Scheele's green?
What are the oxidation states?
Cu = +2
As = +3
H = +1
O = -2 (x3 = -6)
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
What compouds does Scheele's green form when it becomes damp + mouldy?
(they all have the same structure as the pic but with a different no. methyl groups. Arsine has none + has Hs instead)
What are the advantages + disadvantages of the initial test for arsenic?
Involves simple test tube chemisty
Yellow precipitate of arsenic sulphide breaks down quickly
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
Hazardous test (arsine gas)
Not sensitive enough to detect As in hair
What are the advantages + disadvantages of using X-ray fluorscence spectroscopy to test for arsenic?
Can detect extremely minute quanities - smallest of all tests
Gives unique characteristic peaks for atoms - more specific than Marsh Test
Requires specialised, expensive equipment
What are the 3 oxides of arsenic?
Arsenic dioxide - AsO2
Arsenic trioxide - As2O3
Arsenic pentoxide - As2O5
Which element's oxides are the structures of arsenic tri- + pentoxide similar to?
Phosphorous tri- + pentoxide
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