Oxidation and Reduction

[Alyssa McLeod 3E]

In the molecule is Cr2O7(2-), is the charge on the Cr 12+ (since the charge on the O7 totals 14-), or 6+ since there are two chromium atoms? If it's the latter, does that mean the charge on a single oxygen atom is always 2-?

[Paul_Ajodha_2K]

The charge on the Cr is 6+ because we account for only one Chromium ion here and when we look at the reduction on the other side which I believe in that question ended up with Cr3+ so we would say that it reduced from Cr6+ to Cr3+ because we're only considering the one Cr ion on the left side. The reason the molecule Cr2O7(2-) has a net charge of 2- is because there are two Cr atoms both with a 6+. When you add the two Cr atoms and the 7 Oxygen atoms you just end up with a 2- net charge. But to answer your question, the latter of your statement is right and yes the charge on oxygen itself is 2- but don't confuse the fact that the whole molecule is also 2-. The 2- on the molecule doesn't mean Oxygen is also 2-; the 2- on the Oxygen is always implied. I really hope this helped!

[Julie Barreto 3A]

for that same problem, i understand that you have to balance the hydorgen and electrons but why is it 2H+ when there is only 5 on the reactant side and 4 on the product side?

[Julie Barreto 3A]

wait nevermind I got it haha