How to find the Oxidation Number for Cr in K2Cr2O7 (Potassium dichromate)

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in this video we'll find the oxidation

numbers for each element here in k2cr2o7

that's potassium dichromate and we use

these rules here to help find out the

oxidation number so let's take a look

what do we know we know that group 1

potassium is in Group 1 those have a

charge of +1 so the oxidation number is

+1 the chromium we don't know that's not

in our list but we do know that oxygen

is almost always minus 2 with a few

exceptions so each of these seven

oxygens each one is a minus 2 we also

know that in a neutral compound in this

compound here overall has a charge of

zero all of the oxidation numbers have

to add up to that zero there so we have

enough information to figure out the

oxidation number on the chromium's now

let's do that we know two x plus 1

that's 2 plus we don't know the chromium

and then plus 7 times minus 2 that's

minus 14 all of that needs to equal this

zero here so 2 plus 12 that would give

us 14 add the negative 14 we get to 0 so

12 that's what we need but we have two


so we need to take half of that so each

chromium is going to have an oxidation

number of plus 6 2 times plus 6 that

gives us our 12 so in recap we found the

oxidation numbers for the elements we

know then we use this rule here that in

a neutral compound all of those numbers

add up to zero to figure out the one we

didn't know in this case the chromium

this is dr. B with the oxidation numbers

for k2cr2o7 potassium dichromate thanks

for watching