Volumetric Analysis

Question 1

Oxidising Agent

Answer 1

Electron Acceptor

Question 2

Iodine-thiosulfate Titrations

Answer 2

Used to determine conc of an oxidising agent

1. Known vol(25cm3) of solution of o agent placed in conical flask
2. Mixture acidified using Sulfuric Acid
3. Solid excess potassium iodide added
4. Iodine in solution in conical flask titrated w/ standard sodium thiosulfate solution

Question 3

Iodate (v) Ions Reduction

Answer 3

2IO3- + 12H+ + 10e- -> I2 + 6H2O

I from +5 to 0 os

Question 4

Iodide Ions Oxidation

Answer 4

2I- -> I2 + 2e-

Question 5

Combined Ionic Equation Iodate (v) ions

Answer 5

IO3- + 6H+ + 5I- -> 3I2 + 3H2O

1mol iodate prod 3mol Iodine

Question 6

Hydrogen Peroxide Reduction

Answer 6

H2O2 + 2H+ + 2e- -> 2H2O

Question 7

Combined Ionic Equation Hydrogen Peroxide

Answer 7

H2O2 + 2I- + 2H+ -> 2H2O + I2

1mol H2O2 prod 1mol Iodine

Question 8

Iodine with Thiosulfate Ions

Answer 8

Question 9

Colour Changes Iodine-Sodium Thiosulfate Titrations

Answer 9

Add 20cm3 dilute sulfuric acid and 1.5g solid potassium iodide:
Colourless -> Brown

Titrate with Sodium Thiosulfate:
Brown -> Straw/Yellow

Add starch Indicator:
Straw -> Blue-Black

Continue titration with sodium thiosulfate:
Blue-Black -> Colourless

Question 10

Reducing Agent

Answer 10

Electron Donor

Question 11

Potassium Manganate (vii) Titrations

Answer 11

Used to estimate conc of reducing agents

1. 25.0cm3 solution of reducing agent placed in conical flask
2. mixture acidified using Sulfuric Acid
3. Standard solution of Potassium Manganate(vii) added from burette until solution changes from colourless to pink

Question 12

Equation reduction KMnO4 to MnO4-

Answer 12

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

KMnO4 - purple
MnO4- - pink

Mn +7 to +2

Question 13

Iron (ii) Ions Oxidation

Answer 13

Fe2+ -> Fe3+ + e-

Question 14

Combined Ionic Equation Iron(ii) ions

Answer 14

Question 15

Oxalate Ions Oxidation

Answer 15

Question 16

Combined Ionic Equation Oxalate Ions

Answer 16

Question 17

Overall Ratios of Reducing Agents

Answer 17

1mol MnO4- = 5mol Fe2+
2mol MnO4- = 5mol C2O4 2-

Question 18

Solutions in Water

Answer 18

Often Cloudy

Question 19

Back Titration

Answer 19

Method where an excess of s reagent is reacted with a sample
The amount of untreated Reagan is then determined by titration

Question 20

Method Of Back Titration

Answer 20

1. Known mass of solid Group II metal/carbonate/oxide added to known excess of acid - reaction allowed to go to completion
2. Resulting solution may be filled in a volumetric flask
3. Doled solution may then be titrated against a standard solution of NaOH using Phenolphthalein indicator

Colour Change: Colourless -> Pink

Question 21

What is back titration used to determine

Answer 21

Purity of Group II metal, oxide or carbonate