Which of the following is not an example of a redox reaction? bleaching, precipitation, respiration, rusting?
Answer:
Definitely precipitation. In a precipitation reaction the oxidation numbers of the species involve do not change, thus, no electrons are transferred.
NaCl (aq) + AgNO3 (aq) --> AgCl (s) + NaNO3 (aq).
Na+ (+1), Cl- (-1), Ag+ (+1), N (+5), O (-2). The numbers in parenthesis are the oxidation numbers, so they stay the same from beginning to end, so no redox reaction took place.
In bleaching, ClO- is reduced to Cl-, oxidizing whatever it comes in contact with.
In respiration, the O2 oxidizes molecules containing carbon, so we exhale CO2, in which O has a -2 oxidation number, so it decreased from 0 to -2, so O was reduced.
Rusting can be written as 4 Fe (s) + 3 O2 (g) --> 2 Fe2O3 (s), Fe was oxidized to +3 and O was reduced to -2.
This can be a simple redox process, such as the oxidation of carbon to yield carbon dioxide, it could be the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar in the human body, through a series of very complex electron transfer processes.
precipitation
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