manganate VII redox titration key bits.

Question 1

is manganate a reducing or oxidising agent?

Answer 1

oxidising agent

Question 2

what colour is MnO4- solution?

Answer 2

purple

Question 3

what colour is Mn2+

Answer 3

colourless

Question 4

what is MnO4- reduced to?

Answer 4

Mn2+

Question 5

what is the method for the manganate titration?

Answer 5

1) add a standard solution of KMnO4- to a burette
2) yse a pipeete to add a measured volume of solution being analysed to a conical flask.
3) add a known volume of dilute H2SO4 tp provide the H+ ions required for the reduction of MnO4-
4) The end point is the presence of a pink/purple colour solution indicating excess MnO4- ions.
5) repeat titration until you get concordant titres.

Question 6

why is the manganate titration described as self indicating?

Answer 6

because the solution will change colour from colourless to purple pink

Question 7

what are the reducing agents that MnO4- oxidises? -

Answer 7

• Fe2+

- (COOH)2 (oxalic acid)

Question 8

write the reduction half equation of manganate?

Answer 8

• MnO4-(aq) + 8H+(aq) + 5e (aq) —-> Mn2+ + 4H2O(l)

Question 9

when calculating % purity of the salt, do u use the mr of the whole impure salt, or do u discards the .xH2O bit?

Answer 9

the WHOLE SALT.

u only do the salt w/o the H2O when working out the chemical formula

Question 10

what is the oxidation half eqation of (COOH)2 when reacted with MnO4-

Answer 10

(COOH)2(aq) ——-> 2CO2(g) + 2H+(aq) + 2e.

Question 11

what is the oxidatio half equation of Fe.

Answer 11

2Fe2+ ——–> 2Fe3+ + 2e

Question 12

what type of acid should we use the for the manganate titration to supply H+ ions?

Answer 12

a strong acid.

Question 13

why do we add the acid in excess?

- why dont we use weak acids?

Answer 13

• limited amount of acid would produce MnO2 + 2H2O
  MnO2 –> black solid/ppt would mask the colour change leading to greater inaccuracies.
  using a weak acid would have the same effect