REDOX

Question 1

Define Oxidation Number….

Answer 1

Number of electrons an atom uses to bond with an atom of ANOTHER element…

Question 2

Oxidation number of PURE elements|metal Hydrides|O in peroxide|O with F atom

Answer 2

1. PURE = always 0
2. Hydrides (metalH) = Metal = -1
3. O with F atom = +2
4. O in peroxide = -1

Question 3

How to construct a REDOX equation…

Answer 3

1. Find oxidation states and overall charge per equation side!
2. Balance all elements
3. SORT OUT ELECTRONS!
4. SORT OUT OXYGENS via adding H2O
5. Sort out H via adding H+ ions
6. Check overall charges on both sides to finish……..

Question 4

Define Disproportianation

Answer 4

1. where the SAME ELEMENT is both OXIDISED and REDUCED

Question 5

what are oxidising and reducing agents?

Answer 5

1. Does to the OPPOSITE function to itslef, while CAUSING their name to another species….

Question 6

What basics occur during Manganate(VII) Titrations?

Answer 6

1. Manganate ion will be REDUCED to manganese(II) ion, gaining e-
2. Other species present must be REDUCING AGENT in titration, providing the e-
3. SELF-INDICATING: Purple=Manganate ion(burette),
   Colourless=Manganaese(II)(flask)&raquo_space; LIGHT PINK gives end-point (excess MnO4-…)

Question 7

Acid used during Manganate Titration?

Answer 7

1. DILUTE H2SO4: Provides sufficient H+ ions for reduction of MnO4-, without side reactions!
2. NOT HCL = MnO4- would oxidise Cl- present into Cl2, affecting MnO4- vol.
3. NOT CONC SULFURIC/NITRIC ACID = Also oxidising agents gaining e-, will affect total MnO4- vol.
4. NOT ETHANIOC ACID = Very weak acid, partiall ionising = not enough H+ ions

Question 8

What is special about ethanedioate ions in manganate titrations???

Answer 8

1. MUST BE HEATED!
2. To ensure reaction can speed up, as C2O4 2- and MnO4- are both ANIONS, meaning REPULSIONS can take place (and not enough energy for collisions…)

Question 9

What basics occur during Thiosulfate/Iodine Titrations?

Answer 9

1. 2 REACTIONS will always take place!
2. S2O32- becomes oxidised, while Iodine becomes reduced!
3. AND THEN, the resulting Iodide anions produced can be used in SEPERATE reactions (CLO-, Cu2+….) to find analysis and concentrations…
4. Can also be REVERSED for Iodine used instead of IODIDE…

Question 10

Indicator needed during Thiosulfate/Iodine Titrations?

Answer 10

1. STARCH INDICATOR IS NEEDED to provide greater contrast
2. Blue-Black colour turns colourless, signifying point of excess Iodide anions