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chemistry A > 16A.1 > Flashcards

16A.1 Flashcards

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1
Q

oxidation is

A

loss of electrons

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2
Q

reduction is

A

gain of electrons

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3
Q

when an element is oxidized its oxidation number

A

increases

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4
Q

when an element is reduced its oxidation number

A

decreases

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5
Q

standard electrode potential is also

A

redox potentail

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6
Q

standard electrode potential is also

A

redox potential

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6
Q

what happens to metals when they are placed in water

A

they have a very small tendency for them to lose electrons and from a solution of positive ions

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7
Q

how is this (M^n+(aq) + ne^-1 eq M(s)) eq formed

A

when a metal is put in water it loses electrons and forms a positive ion solution, so within a short time, there will be a build-up of electrons on the surface of the metal, due to the electrostatic attraction between the electrons on the surface of the metal and the positive ions formed, some of the positive ions will regain their electrons and become part of the metal surface, eventually a dynamic equilibrium will form

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8
Q

the eq formed between the positive metal ion and its electrons in water is given by

A

M^n+(aq) + ne^-1 eq M(s)

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9
Q

the more reactive the metal in a half-cell is

A

the eq will lie further to the left, which means more significant tendencies to release electrons so greater negative charge on the metal and more positive ions in the solution

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10
Q

what is the absolute potential difference

A

the potential difference between the electrons on the surface of the metal and the solution of positive ions of that metal

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11
Q

what is the rs between absolute potential difference and reactivity of the metals

A

as the metal becomes more reactive the V increases

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12
Q

why can’t we measure the absolute potential difference directly

A

we can connect the metal electrode to one terminal (of the circuit), but the other terminal would have to be connected to the solution which isn’t possible. and we can’t connect the terminal to other metal dipped into the water because then that would create its own potential difference.

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13
Q

how can we measure absolute potential difference of a half cell

A

create a refence potential electrode (standard hydrogen electrode) then measure the potential difference between the reference electrode and the metal electrode

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14
Q

what is the reference electrode of choice

A

standard hydrogen electrode

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15
Q

how does the standard hydrogen electrode work

A

hydrogen gas at pressure of 100KPa (1 bar) being bubbled over a piece of platinum foil covered with porous platinum, dipped into a solution of acid (H2SO4) with [H^+] at 1 mol dm^-3, at temp of 298K

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16
Q

why do we cover platinum with porous platinum

A

it has a large surface area and allows the Eq between hydrogen ions in the solution and the hydrogen gas to be established quickly

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17
Q

what is the standard hydrogen electrode half cell (its half equation)

A

page 161

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18
Q

Importance of using student conditions

A

the position of Eq changes by altering the conditions so fair comparisons we need standard conditions

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19
Q

what are standard conditions

A
  1. 100KPa (1 bar), 298K, concentration in solution of 1 mol dm^-3
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20
Q

what is a half cell

A

it is one half that makes the electrochemical cell, and two half cells complete one cell

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21
Q

how does a metal ion/metal system look like

A

page 161

22
Q

why is a salt bridge needed

A

to complete an electrical circuit

23
Q

what is the salt bridge made from

A

filter or chromatography paper dipped in an a ionic salt (usually potassium nitrate), the salt ions should mot interfere with the components of the half cell

24
Q

equilibrium reaction are written in

A

the reduced form

25
Q

why is a high resistance voltmeter used in an electrochemical cell

A

because we don’t want the electrons (circuit) to flow through it so the potential difference measured from the voltmeter is that of the two half cells

26
Q

the sign of standard electrode potential indicates

A

the polarity of the electrode when compared with hydrogen electrode. the sign is fixed and doesn’t change even of the equation of the half cell is reversed

27
Q

the sign of the electrode depends on (metal)

A

if more reactive than hydrogen its negative, if less reactive than hydrogen its positive (since metal want to lose electrons0

28
Q

what is the standard electrode potential

A

The emf measured when a half-cell is connected to a standard hydrogen electrode under standard conditions

29
Q

the sign of the electrode depends on (non metal)

A

if more reactive than hydrogen then positive, and less reactive than hydrogen then negative (because metals like to gain electrons).

30
Q

the standard electrode potential of hydrogens half cell is

A

0.00 under standard conditions

31
Q

the potential difference provides a comparison between

A

the position of the metal ion/metal eq and the position of eq in the hydrogen electrode

32
Q

what does a negative standard electrode potential mean

A

the equilibrium of the half cell reaction lies further on the left than the eq of the standard hydrogen electrode (the more readily the element loses elections to from ions)

32
Q

what does a positive standard electrode potential mean

A

the equilibrium of the half cell reaction lies further on the right than the eq of the standard hydrogen electrode (the less readily the element loses electrons to form ions)

33
Q

the electrode where oxidation takes place is

A

the anode

34
Q

the electrode where reduction takes place is

A

the cathode

35
Q

what is a reducing agent

A

a species that reduces other species by adding one or more electrons to it . when it reacts it loses electrons, and therefore oxidized

36
Q

what is a oxidizing agent

A

a species that oxidizes another species by removing one ore more electrons from it. when it reacts it gains electrons and therefore reduced

37
Q

what is emf

A

the measured potential difference of a cell when no current is flowing

38
Q

the emf will be positive if

A

the hydrigen electorn is negative (cathode)

39
Q

the emf will be negative if

A

the hydrogen electrode is positive (anode)

40
Q

the standard potential difference of a cell is called

A

E cell, and standard cell potentail

41
Q

the emf polarity depends on (in general)

A

the reference point against which the potential difference is measured

42
Q

how can we setup a system to measure the V of a gas

A

the gas is bubbled into a solution of its ions, in order to establish an eq between the gas and its ions, and to provide a connection the the external circuit, we need to place a piece of platinum into the solution

43
Q

gas/hydrogen system looks like

A

164

44
Q

how can we set up a non metal elements and their ions in solution system

A

The non metal would be put into a solution with its ions, but in order to establish an equilibrium between the non-metal and its ions, and also provide a connection to the external circuit, we would need to place a piece of platinum into the solution.

45
Q

how can we set up a ‘ions of the same element with different oxidation number’ system

A

a solution would be made with both ions, and a platinum metal is put in the solution in order to establish an eq between the ions, and also provide a connection to the external circuit.

46
Q

what is the electrochemical series

A

it is an series built-up by arranging various redox equilibria in order of their standard electrode (redox) potential, with the most positive values on top

47
Q

species on the right-hand side of the half cell half reaction behaves as

A

a reducing agents because they lose electrons.

48
Q

species on the left-hand side of a half cell - half reaction behaves as

A

oxidizing agents because they can gain electrons

49
Q

the more negative the standard electrode potential is

A

the more the eq position lies towards the left, so more readily the species on the right loses electrons therefore more reducing power

50
Q

the more positive the standard electrode potential is

A

the more the eq position lies towards the right, so more readily the species on the left gain electrons therefore more oxidizing power

51
Q

why cant we measure the standard electrode potential of reactive metals and other experimentally

A

because they can react with water to completion, so E us measured from thermodynamic data.

chemistry A (77 decks)

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