R.P 8 (Measuring the EMF of an electrochemical cell) Flashcards
Outline the 4 stages in measuring the EMF of a Zn Cu cell
1) Place the copper strip into a 100 cm3 beaker with
about 50 cm3 of 1 mol dm–3 CuSO4 solution.
2) Place the zinc strip into a 100 cm3 beaker with about 50 cm3 of 1 mol dm–3 ZnSO4 solution.
3) Use a strip of filter paper soaked in saturated
potassium nitrate solution for the salt bridge
4) Connect the Cu(s)|Cu2+(aq) and Zn(s)|Zn2+ (aq) half- cells by connecting the metals using the crocodile clips and leads provided to the voltmeter
Then read off EMF
What do we do to the metal strips before using them to measure the EMF of the cell
Clean the zinc and copper foils with emery before use.
Degrease the metal using some cotton wool and
propanone
What is the salt bridge made out of
A salt bridge is usually made from a piece of filter paper soaked in Potassium Nitrate
State one essential property of the salt bridge
State 1 key feature which must be implemented when setting it up
Salt must be unreactive
Salt bridge must not touch metals, only the solution
Give an example of an inappropriate salt for the salt bride in Cu cells
Potassium chloride would not be suitable for copper systems because chloride ions can form complexes with copper ions.
What do we do if one or both of the half cells do not contain a conductive metal
We must use an inert platinum electrode
How do we set up a Cu Fe Cell
Set up a copper half cell using a similar
arrangement to the previous one. Combine it
with a Fe2+/Fe3+ half-cell with a platinum
electrode.
The half cell with the Pt electrode should have a mixture of acidified 1.0M iron(II) sulphate solution and an equal volume of 0.5M iron(III) sulphate solution as the electrolyte.
Use a fresh salt bridge.
Describe the concentration of the 2 compounds in solution in a half cell with a Pt electrode
Both ion solutions must be of a 1M concentration
e.g. [Fe2+] = 1M and [Fe3+] = 1M
