chem chap 10 - redox

Question 1

explain the 2 problems regarding the use of iron - not easy to extract

Answer 1

iron is not easy to extract from its ores or rocks
to be extracted, reduce compounds in rocks that have iron in them
uses up a lot of energy and chemical processes used, which will cause pollution

Question 2

explain the 2 problems regarding the use of iron - rusting

Answer 2

iron rusts /oxidise easily in a wet climate
iron is a strong hard metal with brittle ionic compounds which may break

Question 3

oxidation can be described as

Answer 3

the gain of oxygen
the loss of hydrogen
the loss of electrons
increase in oxidation state

Question 4

reduction can be described as

Answer 4

the loss of oxygen
the gain of hydrogen
gain of electrons
decrease in oxidation state

Question 5

explain the gain of oxygen during oxidation

Answer 5

when iron rusts, it reacts with oxygen to give hydrated iron(iii) oxide

Question 6

explain the loss of hydrogen in oxidation in the eqn CH4 + 2O2 -> CO2 2H2O

Answer 6

CH4 gains oxygen and loses hydrogen and forms co2 as
Carbon atom gains 2 oxygen atoms
and lost its original 4H atoms

Question 7

explain the loss of electrons in oxidation

Answer 7

when iron oxidises in the presence of oxygen and water it starts to rust sjd iron atoms become Fe3+ ions

charge atoms on iron get larger as iron atoms lose electrons and become ions

Question 8

explain the gain of electrons in reduction

Answer 8

when iron reacts with oxygen directly Fe atom becomes Fe3+ ions

iron oxidises and O2 becomes O2+ ions

iron loses electrons while oxygen gains electrons

Question 9

do both reductuon wnd oxidation occur at the same time?

Answer 9

yes

Question 10

what is oxidation state

Answer 10

charge an atom of an element woukd have if it ecisted as an ion in a compound
can take on a positive or negative whole number or zero

Question 11

if an atom has an increase in positive charges but a decrease in negative charges what process is occuring

Answer 11

oxidation

Question 12

if an atom has a decrease in positive charges but an increase in negative charges what process is occuring

Answer 12

reduction

Question 13

what will the oxidation state be of a compound with no net charge

Answer 13

oxidation states will add up to zero

Question 14

what will the oxidation state be for a ion with a net charge

Answer 14

the oxidation states will add up to that net charge

Question 15

what is rule 0 for determining oxidation states

Answer 15

it applies to all elements
oxidation state 0
atoms of the same element will have no net charge

Question 16

what is rule 1 for determining oxidation states

Answer 16

group 1 elements will have OS of +1
atoms from group 1 will lose 1 electron
group 2 elements will have OS of +2
atoms from group 2 will lose 2 electrons

Question 17

what is rule 2 for determining oxidation states - fluorine in its compounds

Answer 17

fluorine in its compounds will have OS of -1
most reactive non metal
attracts electrons to itself strongly
OS is always -1 for F- ion

Question 18

what is rule 2 for determining oxidation states - hydrogen in its compounds

Answer 18

usually has OS of +1
when it forms compounds with metals the OS is -1

Question 19

what is rule 2 for determining oxidation states - oxygen in its compounds

Answer 19

next most likely to gain electrons
OS state od -2
in peroxides, OS is -1

Question 20

what is rule 3 for determining oxidation states - groups 13-17 in their compounds

Answer 20

OS is based on most common valency
a compound as no net charge
OS states adds up to 0

Question 21

what is rule 3 for determining oxidation states - metallic elements

Answer 21

OS is almost always positive
ion has negative or positive charge
OS will add up to that charge

Question 22

what is rule 4 for determining oxidation states

Answer 22

groups 3-12 in their compounds
proton numbers 57-71/89-103 OS states will always be positive
different OS in their compounds
roman numerals indicate OS present in the named species

Question 23

when OS remains the same did oxidation or reduction occur

Answer 23

neither

Question 24

almost any reaction involving a pure element will be a…

Answer 24

redox reaction as atoms in elements have OS of zero

Question 25

an element that is present as an atom/ion in a compound has OS that is..

Answer 25

non zero

Question 26

what are oxidising agens able to do

Answer 26

oxidise another substance
increase the OS of an element in another substance
gain electrons from the other substance
causes oxidation while being reduced

Question 27

give 3 examples of oxidising agents

Answer 27

oxygen, chlorine, potassium manganate(vii)

Question 28

what are reducing agents able to do

Answer 28

reduce another substance
decrease the OS of an element in another substance
lose electrons to the other substance
causes reduction while beiny oxidised itself

Question 29

give examples of reducing agents

Answer 29

hydrogen
reactive metals
carbon
potassium iodide

Question 30

if reducing agent Y reacts with unknown substance X, what is X?

Answer 30

an oxidising agent

Question 31

what is the potassium iodide test for oxidising agents

Answer 31

add a few drops of aqueous potassium iodide are added into a solution if the unknown substance

Question 32

what are the results for the potassium iodide test

Answer 32

positive test:
mixture turns yellow brown
iodide ions are oxidised to iodine by the oxidation agent

negative test:
no colour change, remains colourless

Question 33

what to do if results of potassium iodide test is too vague

Answer 33

if results is very pale and hard to tell if iodine was produced, add few drops of starch -> solution will turn dark blue if iodine is present

a lot of iodine -> iodine may precipitate as black solid

little iodine -> solution will be pale yellow

Question 34

what is the potassium manganate (vii) test for reducing agents

Answer 34

dark purple aqueous manganate (vii) that has been acidified with little sulfuric used

add a few drops of purple solution added to solution of unknown substance

Question 35

what are the results of potassium manganate (vii) test

Answer 35

positive
manganate (vii) ions are reduced to manganese (ii) ions by reducing agent
-> colourless solution formed

negative
purple solution remains / no colour change