Gen Chem Destroyer Question 108

http://chemistry.about.com/od/chemi...Difference-Between-Molarity-And-Normality.htm

http://dwb4.unl.edu/Chem/CHEM869R/CHEM869RLinks/www.utmem.edu/allied/Solutions/Normality.html

Hope this makes sense

Thanks that kinda makes sense. But how come in question 108 you can only use normality? What's wrong with using the molarity equation?

What version of Destroyer are you using? My question #108 is doesn't deal with normality so I can't see the question. Anyways, you want to use normality when moles of base (OH-) are not in equal concentrations as moles of acid (H+)

Example: for a question with Mg(OH)2 and HBr, you can't just say that Mg(OH)2 will react equally with HBr because there are 2 moles of OH- for every mole of H+ . The normality just takes this into account. So you take the molarity given for Mg(OH)2 and you multiply it by two to get the normality. To get the normality of HBr, you take the molarity and just multiply by one (since there is only 1 OH-).

Normality is always equal to (as in the case of HBr) or greater than molarity (as in the case of Mg(OH)2) Normality can NEVER be less than molarity.

Say the molarity given to Mg(OH)2 is 1M. Well for every 1M of Mg(OH)2, there is 2 OH- molecules inside. Your OH-'s are whats reacting, so you take the molarity and multiply by 2.

normality is something you must learn before the DAT. they know that everyone has studied the M1V1=M2V2 equation but most people don't know that the equation should be written N1V1=N2V2 and they will test you on it. normality is based on how many equivalents an acid or base will yield in solution. is it a monoprotic acid or diprotic? is it monobasic or dibasic? and if it is diprotic/dibasic will it fully dissociate in solution? these things won't effect the molarity but they will effect the normality. good luck!

Ok thanks guys I get it. So I'm basically throwing away the MV=MV equation and using normality.