(Blue) redox equilibria III Flashcards
(Blue) redox equilibria III
what happens when you mix :
zinc sulfate with iron
no change
what happens when you mix :
zinc sulfate with lead
no change
what happens when you mix :
zinc sulfate with magnesium
possibly oxidised decreasing reactivity
effervescence
black ppt
+10oC
what happens when you mix :
copper sulphate with iron
Pale blue soln to Red /black ppt
+6oC
what happens when you mix :
copper sulphate with lead
no change
what happens when you mix :
copper sulphate with magnesium
possibly oxidised decreasing reactivity
solution —> colourless pink ppt.
+ 35oC
write these metals in reactivity
zn
Fe
Cu
Mg
Magnesium> zinc> iron >copper >lead.
The magnitudes of the temperature increases should show a similar pattern.
list in order the reactivity series
compare with the internet
what does negative/positive electrode potential mean
positive electrical potential means that it tends to gain electrons
negative electrical potential means that it tends to loose electrons
what is the definition of standard electrode potential
Standard electrode potential E○
of a standard half cell is the potential of that half cell relative to a standard hydrogen half cell under standard conditions, 100 kPa, 298K 1 mol dm-3.
it is important that you relise the need for a standard i.e all solutions are at 1M , espescially the H+ ions MUST be 1M,
why is H2SO4 of concentration 1 Moledm-3 unsutible ?
because it is di protic therefore 2 moles of [H+] will be released
how does a standard hydrogen electrode work
where hydrogen is pumped into a tube it reacts on the surface of a platnum electrode to form 2 molecues of H+ and release 2 electrons
on the other hand H+ from the HCL solution react with the platnum surface electrode to produce hydrogen (H2) gas
what is a very common salt bridge
KNO3
There is no voltage measured in the circuit until the ’salt bridge’ is connected. Why not?
for this example
zinc is being oxidised
and copper is being reduced
So the half cells are no longer equilibria and Zn —> Zn2+ + 2e-.
The [Zn2+] would increase and the reaction would stop unless ionic neutrality was restored i.e. [+ve ions] = [-ve ions] ( remember there in solution which allows them to get ionised)
This is achieved by ions migrating along the salt bridge.
what is a salt bridge
A salt bridge contains a salt such as potassium nitrate, and is used to connect the two half cells. It enables ions to move in and out of the solution keeping both cells ionically neutral (the total –ve charges = the total +ve charges). The salt is chosen so that it will not react chemically with the ions in either half cell. From solubility studies last year you know that all group 1 ions and all nitrate(V) ions are soluble; therefore potassium nitrate makes a good salt bridge as the ions are always soluble. Other ionic salts can be used for example, KCl.
for this example
zinc is being oxidised
and copper is being reduced
What happens to the concentration of the zinc solution as the reaction proceeds?
What happens to the mass of the zinc electrode?
What happens to the electrons released by the zinc?
What happens to the concentration of the copper solution as the reaction proceeds?
What happens to the mass of the copper electrode?
What happens to the concentration of the zinc solution as the reaction proceeds? increases
What happens to the mass of the zinc electrode? decreases
What happens to the electrons released by the zinc? Along the wire, round the external circuit.
What happens to the concentration of the copper solution as the reaction proceeds? decreases
What happens to the mass of the copper electrode? increases
have a look at core practical 10
https://qualifications.pearson.com/content/dam/pdf/A%20Level/Chemistry/2015/teaching-and-learning-materials/A_level_Chemistry_Core_Practical_10_-_Electrochemical_Cells.pdf
what is the function of the salt bridge
To complete the circuit
The cation concentration would increase around the negative electrode and the reaction would stop unless ionic neutrality was restored i.e. [+ve ions] = [-ve ions]
This is achieved by ions migrating along the salt bridge.
3 Write the order of reactivity of the three metals involved in this experiment.
zinc
copper
silver
4 Explain why you decided this was the order.
Zn > Cu > Ag
Combinations of ½ cells, Zn à Zn2+ + 2e- with both Cu and Ag, Zn was the negative electrode readily oxidised.
Cu à Cu2+ + 2e- with Ag only, Cu was the negative electrode, it was more reactive
how do you calculate emf
it is the diffrence between the two E cell values
in the data book there are values for E cell , what reaction are they all undergoing
reduction or oxidation
reduction
the more positive the more / beter it gets reduced
what is the analoge for writing out a cell diagram
ROOR
on the cell diagram which way is the +ve if you obay the ROOR
left to right
Pt [H2(g)] │ H+(aq) ║ [Fe3+(aq) , Fe2+ (aq)] │ Pt
look above there is a pt with a line seperating it and one that does not have that what does tha mean
the iron pt means that the iron is reacting on the surface of the platnum
while the hydrogen is reacting withing hte platnium
how do you seperate somthing in the same phase in a cell diagram
with a comma
waht is the equation for Ecell
using lhs and rhs
Ecell = RHS - LHS
is the left / right hand side being oxidised or reduced
the left hand side is being oxidised
the right hand side is being reduced
