chem chap 10 - redox Flashcards
explain the 2 problems regarding the use of iron - not easy to extract
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
explain the 2 problems regarding the use of iron - rusting
iron rusts /oxidise easily in a wet climate
iron is a strong hard metal with brittle ionic compounds which may break
oxidation can be described as
the gain of oxygen
the loss of hydrogen
the loss of electrons
increase in oxidation state
reduction can be described as
the loss of oxygen
the gain of hydrogen
gain of electrons
decrease in oxidation state
explain the gain of oxygen during oxidation
when iron rusts, it reacts with oxygen to give hydrated iron(iii) oxide
explain the loss of hydrogen in oxidation in the eqn CH4 + 2O2 -> CO2 2H2O
CH4 gains oxygen and loses hydrogen and forms co2 as
Carbon atom gains 2 oxygen atoms
and lost its original 4H atoms
explain the loss of electrons in oxidation
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
explain the gain of electrons in reduction
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
do both reductuon wnd oxidation occur at the same time?
yes
what is oxidation state
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
if an atom has an increase in positive charges but a decrease in negative charges what process is occuring
oxidation
if an atom has a decrease in positive charges but an increase in negative charges what process is occuring
reduction
what will the oxidation state be of a compound with no net charge
oxidation states will add up to zero
what will the oxidation state be for a ion with a net charge
the oxidation states will add up to that net charge
what is rule 0 for determining oxidation states
it applies to all elements
oxidation state 0
atoms of the same element will have no net charge
what is rule 1 for determining oxidation states
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
what is rule 2 for determining oxidation states - fluorine in its compounds
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
what is rule 2 for determining oxidation states - hydrogen in its compounds
usually has OS of +1
when it forms compounds with metals the OS is -1
what is rule 2 for determining oxidation states - oxygen in its compounds
next most likely to gain electrons
OS state od -2
in peroxides, OS is -1
what is rule 3 for determining oxidation states - groups 13-17 in their compounds
OS is based on most common valency
a compound as no net charge
OS states adds up to 0
what is rule 3 for determining oxidation states - metallic elements
OS is almost always positive
ion has negative or positive charge
OS will add up to that charge
what is rule 4 for determining oxidation states
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
when OS remains the same did oxidation or reduction occur
neither
almost any reaction involving a pure element will be a…
redox reaction as atoms in elements have OS of zero
an element that is present as an atom/ion in a compound has OS that is..
non zero
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
give 3 examples of oxidising agents
oxygen, chlorine, potassium manganate(vii)
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
give examples of reducing agents
hydrogen
reactive metals
carbon
potassium iodide
if reducing agent Y reacts with unknown substance X, what is X?
an oxidising agent
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
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
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
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
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
