chapter 23

Question 1

oxidation number of an atom in an element

Answer 1

0

Question 2

oxidation number of oxygen in hydrogen peroxide

Answer 2

-1

Question 3

oxidation number of oxygen in OF2

Answer 3

+2

Question 4

when is the oxidation number of chlorine not -1

Answer 4

when combined with oxygen or flourine

Question 5

oxidising agent
reducing agent

Answer 5

it takes electrons from the species being oxidised
gives electrons to the species being reduced

Question 6

which ions are present when a reaction is said to be under acidic conditions

Answer 6

H+

Question 7

what do we use to balance
Oxygen, hydrogen and charges in half equations

Answer 7

balance oxygen with water molecules
balance hydrogen with hydrogen ions
balance charges with electrons

Question 8

in manganate (VII) redox titrations, why are the burette readings taken from the top of the meniscus

Answer 8

the deep purple colour of manganate(VII) makes it difficult to see the bottom of the meniscus

Question 9

during manganate (VII) redox titrations, when is the endpoint

Answer 9

when the first permanent pink colour is formed(this indicates a drop excess of manganate )

Question 10

concordant results

Answer 10

results within 0.1cm3 of each other

Question 11

percentage purity formula

Answer 11

(mass of pure substance/ mass of impure substance)* 100

Question 12

purpose of manganate (VII) redox titrations

Answer 12

to analyse any reducing agents

Question 13

outline the processes involved in iodine/thiosulphate redox titrations

Answer 13

excess of potassium iodide added to the oxidising agent being analysed.
the oxidising agent is measured in a pipette
Iodide ions are oxidised to Iodine during this process
the solution turns yellow-brown
mixture is titrated with a standard solution of sodium thiosulphate. the yellow colour fades

Question 14

what color change occurs close to the endpoint in an iodine/thiosulphate redox titration when we add a starch indicator

Answer 14

from straw yellow to a deep blue-black color

Question 15

at the endpoint in an iodine/thiosulphate redox titration, what happens

Answer 15

the blue-black colour disappears ( solution turns colourless )

Question 16

a redox reaction can be split into two half equations, true or false

Answer 16

true

Question 17

half- cell

Answer 17

contains the chemical species present in a redox half-equation

Question 18

what arranges for the two half equations in a redox reaction to occur separately in half cells

Answer 18

a voltaic cell

Question 19

in electrochemical cells …… are transferred from one half-cell to another, and this means….

Answer 19

electrons
current has been generated and chemical energy has been converted into electrical energy)

Question 20

by convention, what does the forward reaction in a half-cell represent

Answer 20

a reduction reaction

Question 21

what happens at the phase boundary

Answer 21

an equilibrium is set up

Question 22

what is required for electrons to flow from one half-cell to the other through wires

Answer 22

two half cells are required for this to happen

Question 23

what is the salt bridge comprised of

Answer 23

filter paper soaked in saturated KNO3

Question 24

function of the salt bridge

Answer 24

allows the ions to flow

Question 25

in an electrochemical cell, in which direction is the movement of electrons

Answer 25

from the half cell with the more negative electrode potential to the one with the more positive electrode potential

Question 26

standard conditions required for standard electrode potentials

Answer 26

298K
1 moldm^-3
100kPA

Question 27

the function of the voltmeter in an electrochemical cell

Answer 27

it measures the potential difference between the two electrodes( measures the Ecell)

Question 28

Ecell stands for

Answer 28

Electrode potential of the cell

Question 29

standard electrode potential

Answer 29

it is a measure of the ability of species to accept electrons(to be reduced)

Question 30

standard electrode potential of a hydrogen half cell

Answer 30

0.00V

Question 31

the more negative the standard electrode potential of a half cell, ….

Answer 31

the greater it’s tendency to lose electrons and be oxidised

Question 32

the more positive the standard electrode potential of a half cell,….

Answer 32

the greater the tendency of gaining electrons and be reduced

Question 33

ion/ion half cells
give one example

Answer 33

this is when the redox system does not contain a metal
the hydrogen half cell

Question 34

in ion/ion half cells, which metal is used as the electrode and why

Answer 34

platinum
because it is inert, it does not participate in the redox reaction while the cell is working, unlike other metals

Question 35

is the half equation flipped for the reduced or oxidized half cell in an electrochemical cell

Answer 35

for the oxidized half cell

Question 36

What are the five rules when balancing half equations

Answer 36

Write down the species before, and after the reaction
Balancing any atoms apart from oxygen and hydrogen
Balance in oxygen is H20
Balance, any hydrogens with hydrogen ions
Balance any charges with elections

Question 37

In half equations where the species are reduced, on which side are the electrons?

Answer 37

On the left side of the equation

Question 38

All feasible reactions provide a………. Value for the electrode potential if the cell

Answer 38

A positive value