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Ib sl chemistry > Topic 9: Redox Processes > Flashcards

Topic 9: Redox Processes Flashcards

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1
Q

What is oxidation?

A

Addition of oxygen to a substance/the loss of one or more electrons from a substance.

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2
Q

What happens when something is oxidized?

A

Reduction - a gain of one or more electrons to a subtances

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3
Q

How to write half equations

A

Separate oxidation (add electrons on product side to balance) and reduction (add electrons on reactant side to balance) reactions

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4
Q

What does increase in oxidation state mean

A

Substance was oxidized

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5
Q

Decrease in oxidation state

A

Substance was reduced

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6
Q

Sum of all oxidation states in a compound = ?

A

0

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7
Q

sum of all ox states in an ion = ?

A

the charge of the ion

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8
Q

Lone elements oxidation state

A

0

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9
Q

Oxygen oxidation state

A

-2 except when in H2O2 it is -1

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10
Q

Hydrogen oxidation state

A

+1 except in metal hydrides (NaH) it is -1

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11
Q

oxidizing agent

A

oxidizes another substance, is reduced itself, is usually in its highest oxidation state (oxidation state lowers when reduced)

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12
Q

Reducing agents

A

readily reduces another substance (donates electrons), is oxidized itself

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13
Q

Example of oxidizing agents

A

O2, Cl2, F2, SO3, (SO4 2- in solution), MnO4- and Cr2O7 2 -

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14
Q

Example of reducing agents

A

H2, Na, C, CO, and SO2 (SO3 2- in solution)

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15
Q

How to identify redox reaction?

A

Change in oxidation state - Note: reactions where an element is uncombined on one side of the equation and combined on the other side must be redox
reactions since there must be a change in oxidation state

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16
Q

Balancing redox reactions for no change in oxygen

A
  1. split into half equations
  2. multiple so that both equations have equal amounts of electrons (so they can cancel out when added together)
  3. put the two half equations together
17
Q

Balance redox reaction for a change in number of oxygen atoms

A
  1. split into half equations
  2. balance out oxygen with water on the other side, then use H+ to balance out the hydrogens on the other side
  3. add up charges on both sides
  4. add electrons to balance the charges
  5. multiply both sides so that the electrons are equal on both sides
  6. put together two half equations
  7. simplify by reducing what is on both sides

(to make an equation basic add OH that will combine with H+ to get rid of them)

18
Q

How to deduce activity series for reducing agents? (more ready to lose?)

A

considering the reactivity of metal with water and acids, and the reaction of metals with the ions of other metals. The more readily a metal loses its outer electrons makes it more reactive.

19
Q

Why can only metals above hydrogen on the activity series react with acids?

A

Because they are able to displace the hydrogen ions.

20
Q

Activity series for oxidizing agents?

A

The more readily they gain electrons, the more reactive (the more electronegative the more reactive of an oxidizing agent it is)

21
Q

What is an application of a redox process

A

winklers method - used to measure BOD which is biological oxygen demand

22
Q

What is BOD

A

biological oxygen demand - measure of the amount of dissolved oxygen (ppm) needed to decompose organic matter in water biologically over a set time period (usually five days)

23
Q

What does a high BOD in polluted water mean?

A

Polluted water unable to replenish oxygen but also have a high BOD will not be able to sustain life.

24
Q

Describe winklers method

A

using ratios of sodium thiosulfate to iodide to mangenese (4) oxide to manganese (2) salt to oxygen –> find the concentration of dissolved oxygen in ppm

25
Q

what is ppm

A

parts per million = [mass of solute (g)/mass of solution (g)]*10^6

26
Q

What are the ratios in winklers method

A

1 O2 : 2 MnO2 and 1 MnO2 : 1 I2 and 1 I2 : 2 S2O3 2- and so 1 O2 : 4 S2O3 2-

27
Q

What is in a voltaic cell?

A

Two half cells - metals in contact with an aqueous solution of its own ions, half cells connected by a salt bridge (free movement of ions) and external wire, electrons flow from negative anode (oxidation) to positive cathode (reduction). Metal higher on the activity series will be oxidized (reducing agent)

28
Q

What is the convention for writing cells in voltaic cell?

A

Cell undergoing oxidation is on left, reduction on right
metal undergoing oxidation/aqueous ion solution || aqueous ion solution/metal undergoing reduction

29
Q

What is anode

A

where oxidation occurs

30
Q

cathode

A

where reduction occurs

31
Q

Electrolytic cell

A

Electrolytic cells cause non-spontaneous redox reactions to occur by providing energy in the form of electricity from an external source (the opposite of a voltaic cell which is from spontaneous redox reactions)
- positive anode and negative cathode
- Occurs in the same tub of electrolytes (electrolytes conduct electricity when molten
- chemically decomposed electrolytes
- battery pumps electrons given in the molten decomposed electrolytes from the anode to the cathode

32
Q

Describe how current is conducted in an electrolytic cell

A

current is conducted by electrons in the wire and within, the ions are completing the circuit and allowing the current to flow.

33
Q

In a voltaic cell what happens to the mass of the anode electrode

A

the mass decreases because its undergoing oxidation and the oxidized ions join the solution

34
Q

In a voltaic cell what happens to the mass of the cathode electrode

A

The mass of the copper increases because the ions are being reduced into the atom.

35
Q

Is a higher or lower metal on the activity series oxidized

A

higher

36
Q

what does the salt bridge do in a voltaic cell, give examples of salts

A

KNO3, KCl, completes the circuit and keeps the half cell electrically neutral (giving them the ions they are giving away..?), negative ions migrate to anode and positive migrate to cathode, salt bridge is chosen so it doesnt interfere with electrolytes in half cells

Ib sl chemistry (12 decks)

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