DAT Destroyer 2010 question

[Dent4Lifee]

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Hey guys, I wanted to know if it was just me or does this question not make sense..DAT destroyer has a solution for it but I dont understand it. The question (General Chemistry #108) is:

If 20 ml of 0.012 M solution of Ca(OH)2 is added to 48 ml of HBr, what is the concentration of the HBr?

Are they are implying that it takes 20 ml of Ca(OH)2 to neutralize all the HBr?
Thanks for your help

 

[namiie]

Hey guys, I wanted to know if it was just me or does this question not make sense..DAT destroyer has a solution for it but I dont understand it. The question (General Chemistry #108) is:

If 20 ml of 0.012 M solution of Ca(OH)2 is added to 48 ml of HBr, what is the concentration of the HBr?

Are they are implying that it takes 20 ml of Ca(OH)2 to neutralize all the HBr?
Thanks for your help

You don't even have to think about neutralization for this problem, really. But if you are, even then you need to find the concentration of HBr first, which you use NaVa = NbVb for. N is normality and V is volume. The normality of calcium hydroxide is 2 (it has two OH) and the normality of HBr is 1. So you need to multiply concentration by the appropriate normality. So it'd be:

(x)(48) = (0.024)(20)

Solving for x, which represents the normality of the HBr, gives you 0.01. Here the normality of HBr is just 1, so you can take the answer as is to also be the concentration of HBr. Thus, concentration of HBr = .01 🙂

 

[Dent4Lifee]

You don't even have to think about neutralization for this problem, really. But if you are, even then you need to find the concentration of HBr first, which you use NaVa = NbVb for. N is normality and V is volume. The normality of calcium hydroxide is 2 (it has two OH) and the normality of HBr is 1. So you need to multiply concentration by the appropriate normality. So it'd be:

(x)(48) = (0.024)(20)

Solving for x, which represents the normality of the HBr, gives you 0.01. Here the normality of HBr is just 1, so you can take the answer as is to also be the concentration of HBr. Thus, concentration of HBr = .01 🙂

Thank you =)