Learning focus
Explain electrochemical and energetic processes using ions, electrons, balanced equations, observations, energy pathways and quantitative evidence.
Method sequence
Clean the object, connect it to the negative terminal, connect the plating metal to the positive terminal, immerse both in a suitable electrolyte and pass direct current.
Coating thickness
Longer electrolysis time and greater current generally increase the amount deposited. However, excessive current can produce a rough or poorly adhering coating.
Uniformity
Electrode spacing, shape, movement of solution and surface cleanliness affect uniformity. The object should be fully immersed without the electrodes touching.
Evaluation
Quality can be assessed by mass gain, visual uniformity and adhesion. A fair investigation changes one variable while controlling time, current, ion concentration, temperature and exposed area as appropriate.
Worked example
If identical objects are plated for 2, 4 and 6 minutes at constant current, mass gain should generally increase with time. A graph can test whether the relationship is approximately linear.
Practical or data skill
Plan an investigation into how plating time affects mass gain. Include repeats, drying procedure and safety.
Examination tip
A specific improvement must address a named problem, such as cleaning to improve adhesion.
Review questions and suggested answers
Question 1
Name two variables affecting coating thickness.
Suggested answer
Current and time.
Question 2
Why must electrodes not touch?
Suggested answer
Touching can short-circuit the cell.
Question 3
How can coating amount be measured?
Suggested answer
By measuring object mass before and after plating.
