the migration of ions

IGCSE chemistry

section 1i 

the migration of ions

 

Introduction

In an electrolysis experiment, the ions migrate towards electrodes of opposite charge. In the first part of this experiment the migration of manganate ions is observed. In the second part of this experiment, silver and chromate ions meet as they migrate towards opposite electrodes. Silver chromate, an insoluble red compound is formed.

 

What to record

Draw a diagram to show the filter paper at the end of both experiments. Mark the ends of the paper with a + or – to show which terminal of the power supply each end is connected to.

 

What to do

 

Part 1

1.     Cut a piece of filter paper slightly smaller than a microscope slide. Draw a faint pencil line across the middle.

2.     Moisten the filter paper with tap water. Fasten the paper to the slide with crocodile clips.

3.     Use forceps to put a small crystal of potassium manganate(VII) in the centre of the paper.

4.     Connect the clips to a power supply set at not more than 20 V DC. Switch on and wait about ten minutes.

 

 

 

Part 2

1.     Cut a piece of filter paper slightly smaller than a microscope slide. Draw a faint pencil line across the middle.

2.     Moisten the paper with tap water. Fasten the paper to the slide with crocodile clips.

3.     At the end of the paper where the positive electrode will be placed, moisten the paper with silver nitrate solution. (Will stain fingers)

4.     At the end of the paper where the negative electrode will be placed, moisten the paper with potassium chromate solution. (Toxic).

5.     Connect the clips to a power supply set at no more than 20 V DC. Switch on and wait about 10 min, or until you see a change.

 

Safety

Wear eye protection.

 

 

Questions

1.     Potassium manganate (VII) consists of two ions ­– potassium ions and manganate (VII) ions. One of these ions is coloured. Which is it likely to be?

2.     From the direction of movement, what does this indicate about the charge on the manganate ion?

3.     What is happening in the second experiment?

4.      The formula of silver nitrate is AgNO₃ and potassium chromate is K₂CrO₄. Write the ionic formula equation for the reaction.