Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: xangelofxdeathx on March 04, 2007, 12:17:46 AM
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Hi, could someone explain to me how to easily calculate the normality of a solution? I'm kind of confused as to how you find the "equivalence" of a certain solution.
These are just some examples that I was wondering about:
1. What is the normality of 6.60g of Barium Hydroxide dissolved in 50.0 ml of water?
My approach/confusion: First, Barium hydroxide is Ba(OH)2, but then am I supposed to look at the barium or the hydroxide? I know that the molarity is 6.60g / 171.33 (g/mol) / .05 L = 0.770 M. But to find the normality, would I multiply the molarity by one or two in this case? (Because Ba has one? or because OH has two?)
2. A lab requires 400 ml of 0.200 M Barium Nitrate. If the barium solution is reduced to pure Barium, what is the solution's Normality?
My approach/confusion: I'm not really sure what I should do for this one. Hmm, if the barium solution becomes just barium, then it would only be Ba (which is just one equivalence), so would the answer just be 0.200 Normality?
3. Potassium dichromate is reduced to violet Cr3+ ions under certain conditions. Calculate the equivalent weight of potassium dichromate.
4. Calculate the normality of a 0.125 M potassium dichromate solution.
For 3 and 4, I couldn't figure out how to do it at all ???
Thanks :)
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In general - your doubts are well founded as questions are ambiguos. You should always start with reaction equation.
http://www.chembuddy.com/?left=concentration&right=normality
1. See link above. Ba(OH)2 is very similar to H2SO4 here.
2. No idea what it means by 'is reduced' - if t means redox reaction (which doesn't make sense, as Ba2+ is too reactive for that) it requires 2 electrons, so normality will be twice the concentration.
3. This one is unambiguous and relatively easy. Write half reaction for dichromate reduction - one equivalent is one electron.