Variable Oxidation States Of Transition Metals

Question 1

How do you combine two half equations?

Answer 1

• check one of the half equations is losing electrons and the other is gaining electrons
• make sure both half equations involve the same number of electrons (multiply until they do)
• add them together, cancelling out the electrons
• cancel anything that appears on both sides
• check it balances

Question 2

How do you work out half equations?

Answer 2

• balance elements (aside from H and O)
• include enough H2O to balance O ‘
• add enough H+ to balance H
• add e- to the most positive side to balance the charge

Question 3

What is the colour of MnO4-? And what colour does it self titrate to?

Answer 3

MnO4- = deep purple
Colourless => pink

Question 4

What is the procedure for a potassium manganate titration?

Answer 4

• make up a solution of the reducing agent in a 250cm^3 volumetric flask
• rinse a Pipette with this solution and Pipette out 25cm^3 into a conical flask
• add excess sulphuric acid to the flask
• add the purple potassium manganate solution of a known conc to the burette
• add the potassium manganate to the conical flask whilst swirling, stop the titration at the first permanent pink colour
• repeat until the results are concordant

Question 5

What is the half equation for manganate?

Answer 5

MnO4- + 8H+ + 5e- => Mn2+ + 4H2O