16A.1

Question 1

oxidation is

Answer 1

loss of electrons

Question 2

reduction is

Answer 2

gain of electrons

Question 3

when an element is oxidized its oxidation number

Answer 3

increases

Question 4

when an element is reduced its oxidation number

Answer 4

decreases

Question 5

standard electrode potential is also

Answer 5

redox potentail

Question 6

standard electrode potential is also

Answer 6

redox potential

Question 6

what happens to metals when they are placed in water

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

the more reactive the metal in a half-cell is

Answer 9

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

Question 10

what is the absolute potential difference

Answer 10

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

Question 11

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

Answer 11

as the metal becomes more reactive the V increases

Question 12

why can’t we measure the absolute potential difference directly

Answer 12

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.

Question 13

how can we measure absolute potential difference of a half cell

Answer 13

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

Question 14

what is the reference electrode of choice

Answer 14

standard hydrogen electrode

Question 15

how does the standard hydrogen electrode work

Answer 15

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

Question 16

why do we cover platinum with porous platinum

Answer 16

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

Question 17

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

Answer 17

page 161

Question 18

Importance of using student conditions

Answer 18

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

Question 19

what are standard conditions

Answer 19

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

Question 20

what is a half cell

Answer 20

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

Question 21

how does a metal ion/metal system look like

Answer 21

page 161

Question 22

why is a salt bridge needed

Answer 22

to complete an electrical circuit

Question 23

what is the salt bridge made from

Answer 23

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

Question 24

equilibrium reaction are written in

Answer 24

the reduced form

Question 25

why is a high resistance voltmeter used in an electrochemical cell

Answer 25

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

Question 26

the sign of standard electrode potential indicates

Answer 26

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

Question 27

the sign of the electrode depends on (metal)

Answer 27

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

Question 28

what is the standard electrode potential

Answer 28

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

Question 29

the sign of the electrode depends on (non metal)

Answer 29

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

Question 30

the standard electrode potential of hydrogens half cell is

Answer 30

0.00 under standard conditions

Question 31

the potential difference provides a comparison between

Answer 31

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

Question 32

what does a negative standard electrode potential mean

Answer 32

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)

Question 32

what does a positive standard electrode potential mean

Answer 32

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)

Question 33

the electrode where oxidation takes place is

Answer 33

the anode

Question 34

the electrode where reduction takes place is

Answer 34

the cathode

Question 35

what is a reducing agent

Answer 35

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

Question 36

what is a oxidizing agent

Answer 36

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

Question 37

what is emf

Answer 37

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

Question 38

the emf will be positive if

Answer 38

the hydrigen electorn is negative (cathode)

Question 39

the emf will be negative if

Answer 39

the hydrogen electrode is positive (anode)

Question 40

the standard potential difference of a cell is called

Answer 40

E cell, and standard cell potentail

Question 41

the emf polarity depends on (in general)

Answer 41

the reference point against which the potential difference is measured

Question 42

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

Answer 42

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

Question 43

gas/hydrogen system looks like

Answer 43

164

Question 44

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

Answer 44

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.

Question 45

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

Answer 45

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.

Question 46

what is the electrochemical series

Answer 46

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

Question 47

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

Answer 47

a reducing agents because they lose electrons.

Question 48

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

Answer 48

oxidizing agents because they can gain electrons

Question 49

the more negative the standard electrode potential is

Answer 49

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

Question 50

the more positive the standard electrode potential is

Answer 50

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

Question 51

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

Answer 51

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