destroyer question 116 gchem section

[boohoo123]

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if 20 ml of .12M solution of ca(oh)2 is added to HBr what is the concentration of HBr.

In this question they used the titration formula V1N1=V2N2
but why did they use that, isnt this just a simple dilution problem?? How do u know when to use that instead of hte m1v1=m2v2?

Also for compound H3C6H5O7, it says it gives off 3 ionizable protons for the normality..why is it only three??

Thank you guys in advance!!!! <33

 

[LetsGo2DSchool]

For the first one...

Since Ca(OH)2 separates into 2 OH- while HBr only separates into one H+, you need to account for this extra OH- which will require an extra H+ to neutralize it.

Thus, Ca(OH)2 will produce (2)(.12M)(0.020L) = 0.0048 moles OH-

Assuming a complete neutralization occurred, you need 0.0048 moles H+

It's essentially the same as using M1V1 = M2V2, but you just have to multiply the M1 by a factor of 2 to account for the extra OH-