Redox reactions

Question 1

How to create an ionic half equation?

Answer 1

1. Write reagents and products
2. Balance atoms present
3. Add hydrogen ions to combine with oxygen to form water
4. Find charges on both sides to add the electrons needed

Question 2

What is the dichromate half equation?

Answer 2

Cr2O7^2- + 14H+ +6e- —> 2Cr^3+ + 7H2O

Question 3

What is the permanganate half equation?

Answer 3

MnO4- +8H+ +5e- —> Mn2+ +4H2O

Question 4

How to combine half equations?

Answer 4

1. Multiply equations to match the number of electrons
2. Combine the equations, cancel out the electrons and balance H+ ions

Question 5

Describe a redox titration

Answer 5

25cm3 of a solution is measured using a volumetric pipette and placed in a conical flask. A second solution is added a bit at a time from the burette, swirling through mixture during addition until a colour change is seen. This procedure is repeated until readings are taken sufficiently close together.

Question 6

Why do many redox titrations not need indicator?

Answer 6

As the colours of the reactants frequently allow end-points to be seen.

Question 7

What colour does potassium dichromate turn in a redox titration?

Answer 7

It goes from a dark orange Cr2O7^2- solution to a green solution of Cr3+ as oxidation takes place.

Question 8

What colour does potassium permanganate turn in a redox titration?

Answer 8

It goes from a purple MnO4- solution to a colourless solution of Mn2+ as reduction occurs.