GChem Kaplan Chapter 10 Question

[DATGal]

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Please help if you can: This question is from the white (light blue) text, acids and bases chapter, # 5.

If 10mL of 1M NaOH is titrated with 1M HCl to pH of 2, what volume of HCl was added ?

The normality part is fine, but the answer goes on to say one will get 20mL of 0.5 M NaCl solution. Why do we know have a 0.5M solution ? I don't understand what happened here. Any takers ? I would really appreciate the help.

Thanks !! 🙂

 

[supraman]

NaOH has an initial volume of 10 mL right? Well then 10 more mL of HCl is added, leaving a total of 20 mL of solution. The amount of NaOH hasn't changed, but the the volume has. How do you find out new volume?

MV = MV

(1M NaOH)(10 mL) = (xM NaOH)(20 mL of new volume)

x= 0.5 M

The concentration of NaOH decreases.

I think I remember this one... does it go on to use an algebraic equation or something? Don't sweat those, know your basics

Ex: Diprotic acid question was on my DAT, the only one also on acid bases

 

[DATGal]

Supraman, you are THE MAN ! Merci beaucoup !! 🙂

And yes, you are right, it does go on to find out how much more HCl must be added, concluding with a dilution.

Thank you for the reassurance and help ! 👍

 

[supraman]

no prob, good luck!

 

[MoooShuuu]

hmm..I'm a little confused.

If 10mL of 1M NaOH is titrated with 1M HCl to pH of 2, what volume of HCl was added ?

I would do MV=MV ...(1M NaOH)(10ml)= (1HCl)(x?vol) So the vol of HCl added is 10 ml. So if you are asked what the new M is then you would use (1M NaOH)(10 mL) = (xM NaOH)(20 mL of new volume). and get .5 M

Is that what you guys are doing here or is there something that I'm missing? Do we do anything with the pH?😕

 

[klutzy1987]

Kaplans sucks Theyre wrong, whats new. There wouldnt be 20 ml there would be more than 20 ml because you need 10 jus to neutralize the NaOH and then a little more to get to PH of 2. This question has been posted 100 times already, however its usually from achiever or topscore and the solution there is correct.

 

[klutzy1987]

http://forums.studentdoctor.net/showthread.php?p=6764025
http://forums.studentdoctor.net/showthread.php?t=530427

Basically the same question, just from topscore.

 

[MoooShuuu]

Thanks, we appreciate it!

 

[supraman]

Its not the right answer, its part of the right answer. It goes on to explain the rest of the answer in the book but the thread start was confused on one part of the explanation. Kaplan is good stuff, got me the DAT science scores I wanted.