What I’ve Learnt Today Section

CHEMISTRY ♥Introduction

Actually, not much to say... This is the part where I revise back what I’ve learnt at my tuition. Sorry for my bad English & I am not that good at CHEMISTRY too. Well, ENJOY!

1. Diagram 2 below shows two type of cell.

Electron flows

Cell A Cell B

DIAGRAM 2

a) Write the formula of all ions present in the copper (II) nitrate solution.

Cu2 + H+ + NO3- + OH-

b) (I) State the observation at the cathode of cell B.

Mass of electrode Increase

(II) State the observation at the anode of cell B.

Mass of electrode decrease

c) (I) Name the reducing agent in the cell B (Form 5)

Copper

(II) Name the product formed at the anode if copper electrodes in cell B are replaced by carbon electrodes.

OH- ~> O2 + H2O + e- (Electron)Balance4OH- ~> O2 + 2H2O + 4e-

So, the product formed is ~> Oxygen (Do not write in symbol)

d) Based in cell A(I) In which direction do electrons flow through the circuit in cell A?

Show your answer in diagram.- We all know electrons flow from Negative to Positive.- In the diagram, we have Magnesium Mg2+ and Copper Cu2+, both

of them is positive.- Based on the diagram electrochemical series, we can see

Magnesium is above Copper.

V

Copper

Magnesium Magnesium (II) Nitrate Solution

Copper (II) Nitrate Solution

Copper

Copper (II) Nitrate Solution

- Thus, Magnesium is Negative and Copper is Positive.

(II) Name the reaction that occurs at the magnesium plate. (Form 5) Oxidation

Mg ~> Mg2+ + 2e-

(III) State the changes in oxidation number for magnesium in this reaction. (Form 5)

Mg ~> Mg2+ + 2e-

0 to +2

(IV) What happens to cell voltage if the copper plate is replaced with silver plate?- Let us look back at the diagram Electrochemical Series.- If the gap between Magnesium (Mg2+) and Silver (Ag+) increase- The reading on the voltage will increase too- Thus the answer is increases

(V) What is the colour change of the electrolyte in cell A?The intensity of the blue colour decreases