7+ Year Member
Feb 10, 2011
Pg. 284
This passage seems to combine titrations with Electrochemistry. There's a regular redox reaction happening here and it's rate of reaction seems to be affecting by another side reaction of titration. Ie. Pb+2 is being taken away by Cr207 so there's less of it left to (ie. less left for reduction) .<--is this correct?

-What's being titrated here: acid/base and how does that related to Equation 1 and 2 on the page? What's a base/acid (in PbCr2O7)?
- Terminology: "higher reduction potential means" more favorable to reduce. ie. E reduction of +2 is higher than 1., or Ereduction of - 0.13 is higher than Ereduction of - 1. 00 ?


Company Rep & Bad Singer
10+ Year Member
May 25, 2007
Titrations do not have to be an acid reacting with a base. The concept is that if you know the moles of Reactant #1, then you can figure out the molarity of Reactant #2 if you know the exact volume needed to react with the Reactant #1 you have. In this case it's Pb2+ (instead of acid let's say) and Cr2O72- (instead of base let's say). The tricky part is that Pb2+ is precipitating with Cr2O72- (rather than undergoing a redox reaction). But, one all of the Pb2+ has crashed out of solution as an insoluble salt, additional Cr2O72- is the oxidizing agent and Zn remains the reducing agent. The Zn is the anode and the Pb2+ solution that becomes the Cr2O72- solution is the cathode.

Keep in mind that some passages will overwhelm you with information and than ask simple questions that as long as you don't get bogged down or freaked out, you'll be able to do.