Prac 8

Question 1

Required Practical 8 Measuring the EMF of a Cell

Answer 1

• Clean strips of copper and zinc using fine-grade sandpaper.
• Degrease the metal using a cotton wool ball and propanone.
• Place the copper into a 100 cm³ beaker with about 50 cm³ of 1 mol dm⁻³ CuSO₄ solution.
• Place the zinc into a 100 cm³ beaker with about 50 cm³ of 1 mol dm⁻³ ZnSO₄ solution.
• Lightly plug one end of the U-tube with cotton wool and fill the tube with the solution of 2 mol dm⁻³ NaCl solution. Plug this end.
• Joint the two beakers with the inverted U-tube.
• Connect the Cu(s) | Cu²⁺(aq) and Zn(s) | Zn²⁺(aq) electrodes to the voltmeter by using crocodile clips and leads.
• Record the voltage.

Question 2

Clean the metal strips with sandpaper. Why?

Answer 2

This removes any oxide layers.

Question 3

Use 1 mol dm⁻³ solutions. Why?

Answer 3

The solutions need not be 1 mol dm⁻³, i.e., standard conditions.

Question 4

Set up the U-tube with NaCl solution. Why?

Answer 4

This is the salt bridge.
Allows the continuous flow of ions
completes the circuit
Solution needs to have ions not present in cell at all.

Question 5

Connect a voltmeter. Why?

Answer 5

The voltmeter sits in parallel and has a high resistance. It measures potential difference (i.e., voltage).

Question 6

Standard hydrogen electrode parts:

Answer 6

Pt wire
Hydrogen gas
298K
100Kpa
Pt black
1moldm-3 H+ (HCl)