chem chap 10 - redox Flashcards

1
Q

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

A

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

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2
Q

explain the 2 problems regarding the use of iron - rusting

A

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

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3
Q

oxidation can be described as

A

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

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4
Q

reduction can be described as

A

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

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5
Q

explain the gain of oxygen during oxidation

A

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

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6
Q

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

A

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

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7
Q

explain the loss of electrons in oxidation

A

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

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8
Q

explain the gain of electrons in reduction

A

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

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9
Q

do both reductuon wnd oxidation occur at the same time?

A

yes

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10
Q

what is oxidation state

A

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

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11
Q

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

A

oxidation

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12
Q

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

A

reduction

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13
Q

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

A

oxidation states will add up to zero

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14
Q

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

A

the oxidation states will add up to that net charge

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15
Q

what is rule 0 for determining oxidation states

A

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

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16
Q

what is rule 1 for determining oxidation states

A

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

17
Q

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

A

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

18
Q

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

A

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

19
Q

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

A

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

20
Q

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

A

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

21
Q

what is rule 3 for determining oxidation states - metallic elements

A

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

22
Q

what is rule 4 for determining oxidation states

A

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

23
Q

when OS remains the same did oxidation or reduction occur

24
Q

almost any reaction involving a pure element will be a…

A

redox reaction as atoms in elements have OS of zero

25
an element that is present as an atom/ion in a compound has OS that is..
non zero
26
what are oxidising agens able to do
oxidise another substance increase the OS of an element in another substance gain electrons from the other substance causes oxidation while being reduced
27
give 3 examples of oxidising agents
oxygen, chlorine, potassium manganate(vii)
28
what are reducing agents able to do
reduce another substance decrease the OS of an element in another substance lose electrons to the other substance causes reduction while beiny oxidised itself
29
give examples of reducing agents
hydrogen reactive metals carbon potassium iodide
30
if reducing agent Y reacts with unknown substance X, what is X?
an oxidising agent
31
what is the potassium iodide test for oxidising agents
add a few drops of aqueous potassium iodide are added into a solution if the unknown substance
32
what are the results for the potassium iodide test
positive test: mixture turns yellow brown iodide ions are oxidised to iodine by the oxidation agent negative test: no colour change, remains colourless
33
what to do if results of potassium iodide test is too vague
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
34
what is the potassium manganate (vii) test for reducing agents
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
35
what are the results of potassium manganate (vii) test
positive manganate (vii) ions are reduced to manganese (ii) ions by reducing agent -> colourless solution formed negative purple solution remains / no colour change