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Chemistry 5.2.3 - Redox and electrode potentials > Redox > Flashcards

Redox Flashcards

1
Q

What are oxidation numbers?

A

A set or rules that apply to atoms
They are always zero for elements

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2
Q

What are the special cases for oxidation numbers?

A

H in metal hydrides = -1 (NaH) (CaH2)
O in peroxides = -1 (H202)
O bonded to F = +2 (F20)

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3
Q

What are the 3 methods to construct a redox reaction?

A
  • using 2 half equations
  • using oxidation numbers
  • predicting the missing species
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4
Q

What are the steps of constructing redox reactions?

A
  • Balance the electrons
  • Add or cancel the electrons
  • Finally, add the species on both sides of the equation
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5
Q

How do you find a redox reaction using oxidation numbers?

A
  • write the full equation
  • assign the oxidation numbers to atoms that have changed
  • balance the oxidation numbers
  • balance any remaining atoms
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6
Q

How do you find a redox reaction using predicting products?

A
  • assign oxidation numbers
  • balance the electrons
  • balance and predict further species, this is only H+, O or H20
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7
Q

Try all three examples in notes.

A
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8
Q

What occurs in manganate titrations?

A
  • they use transition elements to allow us to find how much oxidising agent is needed to exactly react with a quantity of reducing agent
  • Mn04- ions are reduced to form Mn2+ ions, therefore the other chemical agent must be reducing agent and is oxidised
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9
Q

What is the equation of maganate titrations and Fe2+ as the reducing agent?

A

Mn04- + 8H+ + 5Fe2+ = Mn2+ + 4H20 + 5Fe3+

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10
Q

What is the half equation for the reduction of manganate reaction?

A

Mn04- + 8H+ + 5e- = Mn2+ + 4H20

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11
Q

What is the half equation for the oxidation of iron reaction?

A

Fe2+ = Fe3+ + e-

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12
Q

What is the equation of maganate titrations and (COOH)2 as the reducing agent?

A

2Mn04- + 5(COOH)2 = 2Mn2+ + 10CO2 + 8H20

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13
Q

What is the oxidation of (cooh)2

A

(COOH)2 = 2Co2 + 2H+ + 2e-

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14
Q

What is another oxidising agent other than manganate?

A
  • chronium ions, Cr207 2-
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15
Q

What is the half equation for the oxidation of chronium?

A

Cr207 + 6e- + 14H+ = 2Cr3+ + 7H20

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16
Q

What is the equation for chronium titrations and Fe2+ as the reducing agent?

A

Cr207 2- + 6Fe2+ + 14H+ = 2Cr3+ + 6Fe3+ + 7H20

17
Q

What is the equation for chronium titrations and (COOH)2 as the reducing agent?

A

Cr2072- + 6(COOH)2 + 8H+ = 2Cr3+ + 12Co2 + 7H20

18
Q

What is oxidised and reduced in an iodine - thiosulfate?

A
  • Thiosulfate ions are oxidised
  • Iodine is reduced
19
Q

What can you determine in an iodine - thiosulfate titration?

A

The concentration of aqueous iodine can be determined by the titration with a standard solution of sodium thiosulfate

20
Q

Write the oxidation of thiosulfate ions, the reduction of iodine ions and the overall redox equation for a iodine/thiosulfate redox titration.

A

Oxidation = 2S2032- = S4062- + 2e-
Reduction = I2 + 2e- = 2I -
Overall = 2S2O32- + I2 = 2I- + S4062-

21
Q

What are the other oxidising agents that can be used in an iodine - thiosulfate titration?

A
  • chlorate (I), ClO-
  • Copper (II), Cu2+
22
Q

What is the procedure for a iodine/thiosulfate redox reaction?

A
  • Add a standard solution of Na2S203
  • Prepare a solution of the oxidising agent to be analysed. Use a pipette to add this to a conical flask.
  • Add the excess of potassium iodide
  • The oxidising agent reacts with iodide forming iodine, a yellow brown colour
  • Titrate this with Na2S203.During this titration, iodine is reduced back to I- and the brown colour gradually fades. This makes it hard to determine an end point
  • Therefore starch can be added when iodine reaches a pale colour. This produces a deep blue/black colour. As more sodium thiosulfate is added, the blue/black colour gradually fades
  • At the end point, the blue - black colour disappears
23
Q

What are the before and after redox reactions for a thiosulfate reaction, using Cl0- as an oxidising agent?

A

Before = Cl0- + 2I- + 2H+ = Cl- + I2 + H20
After = 2S203 2- + I2 = 2I- + S406 2-

24
Q

What are the molar rations of CL0: I2: S2032-

A
  • 1 mol CLO- produces one mole of I2 which reacts with 2 moles S2032-
  • therefore, one mole of Cl0- is equivalent to 2 mol S2032-
25
Q

What are the before and after redox reactions for a thiosulfate reaction, using Cu2+- as an oxidising agent?

A

Before = 2Cu2+ + 4I- = 2CuI + I2
After = 2S203 2- + I2 = 2I- + S4062-

26
Q

What are the molar rations of 2Cu2+: I2: S2032-

A
  • 2 mol Cu2+ produces one mole of iodine which reacts with 2 moles of S203
  • so, one mole cu2+ is equivalent to one moles s2032-

Chemistry 5.2.3 - Redox and electrode potentials (4 decks)

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