Experiment 3

The standard electrode potentials (E°) for the relevant half-reactions are:

Fe2+(aq)+2e- ⇌ Fe(s) E ° =-0.44V

Cu2+(aq)+2e- ⇌ Cu(s) E ° =+0.34V

E°cell = E°right hand side - E°left hand side

(0.34V)−(−0.44V)=0.78V

Therefore, the predicted value is E°cell is 0.78V.

This value is predicted because copper is less reactive (less powerful reducing agent)than iron, meaning iron
will lose electrons (oxidation at the anode) and copper will gain electrons (reduction at the cathode).

This value may have occurred due to Impurities in Electrodes or Solutions.If the iron or copper electrodes had
impurities or oxidation (like rust on iron), electron transfer might have been hindered as ionic compounds are
do not conduct electricity.

Experiment 4

A 50cm3 measuring cylinder and a 10cm3 will be used to prepare solutions 50cm^3 of 0.1moldm-3 and 0.01 mol
dm-3 respectively.
To prepare the 0.1 mol dm-3 5cm3 of 1mol dm-3 Copper (II) sulphate solution will be measured out using a 10cm 3
measuring cylinder .45cm3 of distilled water will be measured out using a 50cm 3 measuring cylinder. Then pour
the respective solutions inside a glass beaker and mix them

To prepare the 0.01 mol dm-3 5cm3 of 0.1mol dm-3 Copper (II) sulphate solution (that would be made 1st) will be
measured out using a 10cm3 measuring cylinder .45cm3 of distilled water will be measured out using a 50cm 3
measuring cylinder. Then pour the respective solutions into a separate glass beaker and mix them.

The percentage uncertainties for the 1st preparation of 0.1 mol dm^-3 is as follows:

For the 5cm3 of 1mol dm-3 Copper (II) sulphate solution will be measured out using a 10cm 3 measuring cylinder
the calculation is ±0.1/5cm3*100=2%

45cm3 of distilled water will be measured out using a 50cm3 measuring cylinder the calculation is
±0.5/45*100=1.11%(3sf)

Therefore, the total percentage uncertainty for 0.1 moldm-3 is 2%+1.11%=3.33%(3sf)

The percentage uncertainties for the 2nd preparation of 0.01 mol dm^-3 is as follows:

For the 5cm3 of 0.1mol dm-3 Copper (II) sulphate solution will be measured out using a 10cm^3 measuring
cylinder the calculation is ±0.1/5cm3*100=2%

45cm3 of distilled water will be measured out using a 50cm 3 measuring cylinder the calculation is
±0.5/45*100=1.11%

Therefore, the total percentage uncertainty for 0.01 moldm-3 is 2%+1.11%=3.33%

An alternative method of preparing 0.01 mol dm-3 could have been used :49.5cm^3 of distilled water measured
out using 50cm3 measuring cylinder and measuring out 0.5cm3 of 1mol dm-3 copper (II) solution using a 10 cm3
measuring cylinder.

The percentage uncertainties for this potential preparation of 0.01 mol dm^-3 is as follows:
±0.1/0.5cm3*100=20% for the 0.5cm^3 of 1 mol dm^-3 copper (II) sulphate. And for the 49.5cm^3 of distilled
water measured out using 50cm3 measuring cylinder the percentage uncertainty would be
±0.5/49.5*100=1.01%(3sf)

Therefore, the total percentage uncertainty for this potential preparation of 0.01 mol dm -3 would be 21.01%.
This total percentage uncertainty is higher than the total percentage uncertainty of 2nd preparation of 0.01 mol
dm^-3.

The independent variable is the concentration of Cu2+ ions in the electrolyte of the Cu2+(aq)/Cu(s) half-cell.

The dependent variable is the voltage (EMF) of the cell.

Control variables are as follows:

Electrode Surface Preparation – The zinc and copper foils should be cleaned with emery paper to remove any
oxidized layer .This ensures consistent surface reactivity.

Volume of Electrolyte Solutions – Each half-cell should contain exactly 100 cm³ of the electrolyte solution to
maintain a constant ion concentration and ensure accurate comparisons.

Concentration of Zn²⁺ Solution – The zinc sulfate solution should always be 1.0 mol dm⁻³ throughout all trials to
keep Zn²⁺ concentration constant. Use a high-resistance voltmeter to measure EoCell , as it draws negligible
current. This prevents rapid changes in ion concentration from excessive electron flow.

Temperature – The experiment should be conducted at the same temperature, ideally at room temperature (in
the same room) (~298K), as temperature fluctuations can affect the electrode potentials.

Salt Bridge Composition– Use a Fresh Salt Bridge for Each Trial. Prepare a new strip of filter paper soaked in
saturated potassium nitrate solution before each experiment. To Ensure the Same Type and Concentration of
Salt Bridge Solution. Use saturated potassium nitrate (KNO₃) in all trials to maintain consistency. Use the Same
Size and Material of the Salt Bridge. Cut filter paper strips to the same length and width to ensure uniform ion
flow.
Surface Area of Electrodes: Ensure that all electrodes (e.g., copper and zinc) have the same dimensions
(length, width, thickness). Use pre-cut metal sheets or standard metal strips of the same size.

Based on this equilibrium Cu2+(aq)+2e- ⇌ Cu(s) a decrease in the concentration of Mn+ would move the
equilibrium to the left (according to le Charlier’s principle ), so making the potential less positive as more
electrons are released. Since the potential at the zinc anode remains constant (as its concentration is
unchanged), the overall ECell value decreases. This follows the equation: (E°cell = E°right hand side - E°left hand side ) where
a less positive cathode potential results in a lower overall E°cell .

https://www.scisheets.co.uk/wp-content/uploads/2023/06/Chemsheets-A2-1076-Electrochemistry-booklet.pdf
(accessed 20/03/2025 14:04)

Risk Assessment

Hazard Risk Controll variables

1 mol dm^-3 of Copper (II) Corrosive ,Irritant Use Gloves when handling
sulphate 50cm^3 Wear eye protection
If contact is made with skin ,wash
with copious quantities of
water .Clean up any spillages with
plenty of water using gloves
Don’t swallow
0.1 mol dm^-3 of Copper (II) Corrosive ,irritant Use Gloves when handling
sulphate 50cm^3 Wear eye protection
If contact is made with skin ,wash
with copious quantities of
water .Clean up any spillages with
plenty of water using gloves
Don’t swallow
0.01 mol dm^-3 of Copper (II) Currently not classified as N/A
sulphate 50cm^3 hazardous
1 mol dm^-3 of Iron (II) sulphate Irritant Use Gloves when handling
50 cm^3 Wear eye protection
If contact is made with skin ,wash
with copious quantities of
water .Clean up any spillages with
plenty of water using gloves
Don’t swallow
1 mol dm^-3 of Zinc sulphate 50 Corrosive Use Gloves when handling
cm^3 Wear eye protection
If contact is made with skin ,wash
with copious quantities of
water .Clean up any spillages with
plenty of water using gloves
Don’t swallow
Zinc Metal Currently not classified as N/A
hazardous
Iron metal Currently not classified as N/A
hazardous
Copper metal Currently not classified as N/A
hazardous

CLEAPSS (2022). STUDENT SAFETY SHEETS 3rd Edition 2022. [online] CLEAPSS. CLEAPSS. Available at:
https://science.cleapss.org.uk/Resource/All-in-one-Student-Safety-Sheets.pdf.Date of access (20/03/2025)