RP8 - Measurinf the EMF of an electrochemical cell

Question 1

what’s the method

Answer 1

• clean the zinc and copper foils with emery before use . Degrease the metal using some cotton wool and propanone
• place copper strip into 100cm3 beaker with about 50cm3 of 1moldm-3 CuSO4 solution
• place the zinc strip into a 100cm3 beaker with about 50cm3 of 1moldm-3 ZnSO4 solution
• use a strip of filter paper soaked in saturated potassium nitrate solution for the salt bridge
• 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

Question 2

what’s the salt bridge used for

Answer 2

to connect up the circuit
The free moving ions conduct the charge

Question 3

what’s a salt bridge made out of

Answer 3

from a piece of filter paper soaked in a salt solution , usually potassium nitrate .
It can also be a glass U tube containing a salt solution plugged with cotton wool

Question 4

why is potassium nitrate a good salt solution for the salt bridge

Answer 4

it is in reactive with the electrodes and electrode solution . E.g potassium chloride would not be suitable for copper systems because chloride ions can form complexes with copper ions

Question 5

why is a wire not used as a salt bridge

Answer 5

because the metal wire would set up it’s own electrode system with the solutions

Question 6

why is a platinum electrode used

Answer 6

because it is unreactive and can conduct electricity