Elements From The Sea Flashcards
What is the equation for percentage atom economy?
Atom economy = (molecular mass of desired products/sum of all products) x 100
Is the anode positive or negative?
Positive
Is the cathode positive or negative
Negative
What characteristic should electrodes have?
Inert so they don’t react
What are rules at the cathode for aqueous solutions
If the metal is less reactive than hydrogen it will be formed
If it is more reactive (group 1 and 2 and aluminium) hydrogen gas is formed
What rule for the anode for an aqueous solution
If it doesn’t contain a halide, or is a dilute solution containing a halide, oxygen will be formed
How can halogens be extracted?
Electrolyse concentrated solution containing halogens
In electrolysis where are halogens released
Is it oxidation or reduction
Anode
Oxidation
What is brine
A solution of water with a high concentration of salts - mainly sodium chloride but also some bromine and iodine salts
Why do you have to use concentrated halide solutions for electrolysis?
Because in dilute solutions they’re not discharged
How are bromine and iodine produced from brine?
Bubbling chlorine gas displaced it
it is then collected condensed and purified
What is an electrolyte?
liquid that contains free ions so can conduct electricity in electrolysis
What electrodes are used for aqueous solutions? why?
Platinum or graphite because they’re inert
How do you do electrolysis of an aqueous solution?
- Connect the electrode at the anode to the positive pole and the electrode at the cathode to the negative pole
- Put electrodes in beaker with the electrolyte, making sure electrodes aren’t touching
- turn on power supply
What will the half equation at the anode show?
negative ions losing electrons to form atoms
What will the half equation at the cathode show?
positive ions gaining electrons to form atoms
What does a molten ionic compound break into in electrolysis?
Its elements
Where and how does brine naturally occur?
salt lakes or as sea water
by rock salt dissolving in water
What happens at the cathode during the electrolysis of brine?
Hydrogen ions accept electrons to become one hydrogen gas molecule
What happens at the anode during the electrolysis of brine
Chlorine gas is formed
What is an oxidation state?
How many electrons it has donated or accepted to form an ion or bond
What electron state do O2 and Ag ?
0
What is the oxidation state for an ion of 1 atom (Na+)?
The same as its charge (Na+ would be +1)
What is the overall oxidation state for a molecular ion?
The same as the overall charge
What is combined oxygens usual oxidation state?
-2
What is the usual oxidation state of combined hydrogen?
+1
What is the overall oxidation state of a neutral compound?
0
What does it mean if an ion ends in -ate? (sulfate)
Made of oxygen and another element
sulfur and oxygen
What is (NO3)- called?
nitrate(V)
What is (SO4)2- called?
Sulfate(VI)
What is (CO3)2- called?
carbonate
What is (MnO4)- called?
Manganate(VII)
What is OH- called?
Hydroxide
What is (NH4)+ called?
Ammonium
What is (HCO3)- called?
hydrogencarbonate
What is (S)2- called?
Sulfide
What is (SO4)2- called?
Sulfate(VI)
What is (SO3)2- called?
Sulfate(VI)
What is oxidation?
loss of electrons
What is reduction?
gain of electrons
What happens to reducing agents?
They are oxidised and donate electrons
What happens to oxidising agents?
They are reduced and accept electrons
What are iodine-sodium thiosulphate titrations used for?
Finding the concentration of an oxidising agent
How do you clean the burette for titration?
rinse it out with the solution going in it (eg. sodium thiosulphate)
- using water will leave traces which will dilute the solution
What is the equation for concentration?
conc = moles/vol(dm^3)
What do you add so you can see the end point easier in iodine-sodium thiosulphate titrations? When?
Starch solution - when the solution turns pale yellow
What is the end point for an iodine - sodium thiosulphate titration?
Blue –> clear
clear when the iodine has reacted
What is the end point?
the point where the alkali is exactly neutralised and the indicator changes colour
What are halogens?
Group 7 elements
What does fluorine look like at room temp?
pale yellow gas
What does chlorine look like at room temp?
yellow-green gas
What does bromine look like at room temp?
red-brown liquid
What does iodine look like at room temp?
Shiny grey solid
What is volatility?
Measure of how easy it is to vaporise something?
What is the volatility trend of halogens? why?
Less volatile down the group
because the increase in size and relative atomic mass so stronger id-id bonds
Why do halogens have higher solubility in hexane?
It is an organic solvent
Halogens are covalent and non polar
What colour is chlorine in water?
virtually colourless
What colour is chlorine in hexane?
virtually colourless
What colour is bromine in water?
orange
What colour is bromine in hexane?
red
What colour is iodine in water?
Brown
What colour is iodine in hexane?
violet
What is the reactivity trend of halogens?
Less reactive down the group
Are halogens reducing or oxidising agents?
oxidising agents - gain an electron
Why are halogens less reactive down a group?
larger atoms have more electron shells so outer electrons are further from nucleus
outer electrons more shielded from positive nucleus
so weak attraction to electron needed to form an ion
What can halogens do to less reactive halide ions in solution?
Displace it
What is reduced and what is oxidised in a displacement reaction between halogens and halides?
the displaced halid is oxidised
the displacing halogen is reduced
What can you see with a halogen-halide displacement reaction?
colour change
How can you make a hydrogen halide?
Add a conc acid to a solid ionic halide
eg. conc phosphoric acid to sodium chloride
What hydrogen halides can’t you make with conc sulfuric acid? why?
hydrogen bromide/iodide
iodine and bromine can reduce sulfuric acid and become bromine or iodine gas
What is the trend in bond energy for hydrogen halides?
Decreases down the group
so HF would be more stable than HI when heated
Why does bond energy decrease down the group for hydrogen halides?
Bigger atoms so bonding electrons are
further away and
shielded from the nucleus
Why are hydrogen halides acids in water?
It dissociates into the halogen ion and proton
Why do you get an ammonium halide from hydrogen halide and ammonia?
Ammonia is a base
It accepts proton to form an ammonium ion
which bonds with halide ion
What equation shows sodium chloride reacting with sulfuric acid?
NaCl + H2SO4 –> HCl + NAHSO4
Which hydrogen halide is most thermally stable? why?
HF
Smallest so
strongest attraction to bonding electrons
What acid work for all hydrogen halides when trying to make hydrogen halides from ionic halides?
Phosphoric acid
What is a test for halides?
Use silver nitrate solution - a precipitate of silver halide is formed
What precipitate is formed when fluoride reacts with silver nitrate?
no precipitate
What precipitate is formed when chloride reacts with silver nitrate?
white precipitate
What precipitate is formed when bromide reacts with silver nitrate?
cream precipitate
What precipitate is formed when iodide reacts with silver nitrate?
yellow precipitate
What do you use to tell apart the precipitates formed, in the test with silver nitrates and halides?
Ammonia solution
How does AgCl react with ammonia solution?
dissolves to colourless in dilute ammonia solution
How does AgBr react with ammonia solution?
dissolves to colourless in conc ammonia solution
How does AgI react with ammonia solution?
Does not dissolve so stays the same
Why is chlorine dangerous?
- toxic
- corrosive
- flammable
What is the equation for percentage atom economy?
(molecular mass of desired product) / (sum of molecular mass of all products)
Is better to have a high or low atom economy? why?
High atom economy
they produce less waste so they’re cheaper and more environmentally friendly
What is dynamic equilibrium?
The forward reaction and backward reaction reaction are the same rate
What system does dynamic equilibrium need to be in?
A closed system
Will there be more reactants or products when equilibrium is to the left?
more reactants
Will there be more reactants or products when equilibrium is to the right?
more products
What is Kc?
The equilibrium constant
What is the Kc equation?
[PRODUCTS]/[REACTANTS]
A+ B –> C + 2D
[C] [D]^2 / [A] [B]
What does it mean if Kc is more than 1?
equilibrium lies to the right
What does it mean if Kc is less than 1?
Equilibrium lies to the left
What does it mean if Kc is 1?
Equilibrium is in the middle (amount of reactants and products are equal)
How does Kc stay constant?
the position of equilibrium shifts to keep it constant
What does increasing pressure do to equilibrium?
Equilibrium shifts to side with fewer gas molecules
What does decreasing pressure do to equilibrium?
Equilibrium shifts to side with more gas molecules
What does increasing temperature do to equilibrium?
Equilibrium shifts to endothermic side
What does decreasing temperature do to equilibrium?
Equilibrium shifts to exothermic side
