Normality Question! how to solve this? kaplan sucks at explaining

[demolitionlvr]

What is the normality of a 1M solution of H3PO4 if titrated with CaCl2?

The answer is 1.5 but Kaplan doesn't explain very well why that other than the fact that there are 3 equivalents.

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[Troyvdg]

 

[rockclock]

maybe someone else will chime in, I not too good at normality ish, but i think:

since H3PO4 is an acid, you are looking for the number of equivalents of base it would take to neutralize it.

for every 1 mol of H3PO4, you have 3 H
and for every 1 mol of CaCL2 you only have 2 Cl

therefore you would need 1.5 mols of CaCl2 to get 3 Cl to neutralize the 3 H from H3PO4

Cl- does not "neutralize" H+...HCl is a strong acid and those two ions are going to stay dissociated in solution.

This is your reaction (precipitation):

3Ca^2+ (aq) + 2PO4^3- (aq) --> Ca3(PO4)2 (s)

1 M PO4^3- solution is going to require 1.5 M Ca^2+ if you notice to 3:2 stoichiometric ratio above. That's what the question is asking.

 

[mh0000]

I hope I don't sound too stupid here, but I'm not convinced this is a normality question in regards to the number of protons, as Cl- is not going to react with H+. I'm also thinking the question might be asking about the normality of CaCl2??????
If so, then this MIGHT be what they're after: A precipitate will form between Ca(2+) and PO4(3-). Even though phosphoric acid is a weak acid (especially amongst its second and third dissociation), the precipitation will drive the complete ionization of phosphoric acid to its phosphate anion (very slowly I presume). Therefore, if we think of the normality in terms of charges, then N(PO4(3-))M(PO4(3-)) = N(Ca(2+))M(Ca(2+))

3*1 = 2*x => x=1.5

Again, this is only assuming the question is really asking for the normality of CaCl2.

What do guys think?

EDIT: Looks like rockclock beat me to it, and with a more concise and less convoluted answer

 

[Josh779]

Cl- does not "neutralize" H+...HCl is a strong acid and those two ions are going to stay dissociated in solution.

This is your reaction (precipitation):

3Ca^2+ (aq) + 2PO4^3- (aq) --> Ca3(PO4)2 (s)

1 M PO4^3- solution is going to require 1.5 M Ca^2+ if you notice to 3:2 stoichiometric ratio above. That's what the question is asking.

have you taken your DAT yet rockclock?

 

[rockclock]

have you taken your DAT yet rockclock?

sure have...applied last cycle. I just poke around and answer a few questions every now and then so I'm not completely rusty/brain dead when I start school in a couple months haha.

 

[rockclock]

P.S. for anyone who's interested, doing this problem wrong as a H+/Cl- calculation still gives you the right answer because both those ions are, by coincidence, monovalent (+/-1 charge)...don't count on that happening all the time.

 

[yappy]

Rockclock is DAT-God. It's as if he created the DAT. He cannot be foiled and we should all worship him for his greatness!

have you taken your DAT yet rockclock?

 

[rockclock]

haha thanks yappy, but it's really just that I pick and choose which questions to answer and keep my mouth shut when I don't know what I'm talking about. people getting on these forums and making the situation worse instead of better by giving wrong answers is a huge pet peeve...it's one thing to say that you're just throwing something out there (nothing against what Troyvdg did ), it's another when people build themselves up saying they've tutored, gotten A's, etc. and then spread misinformation...that's usually when I butt heads with those d-bags haha

 

[Josh779]

How did you do on your DAT? I always end up learning something from your solutions.

 

[rockclock]

How did you do on your DAT? I always end up learning something from your solutions.

thanks man...glad it's helping someone.

i scored pretty highly actually...think my lowest section score was a 24. I felt like I was going to have a strong showing, but a little bit of luck was definitely on my side, especially on the bio haha. anyways, don't want to pin it down any further than that...

 

[yappy]

What do you think is the most effective way to get to your level of skill & score that well on the dat? I have about two months left before my fall term starts and would love to hit a score around your lowest! lol.

Thanks.

thanks man...glad it's helping someone.

i scored pretty highly actually...think my lowest section score was a 24. I felt like I was going to have a strong showing, but a little bit of luck was definitely on my side, especially on the bio haha. anyways, don't want to pin it down any further than that...

 

[rockclock]

What do you think is the most effective way to get to your level of skill & score that well on the dat? I have about two months left before my fall term starts and would love to hit a score around your lowest! lol.

Thanks.

for sure the way to attack TS is to lockdown GC and OC:

- for OC I used this (http://pubs.acs.org/doi/abs/10.1021/ed084p1224) as the master plan of what the study and filled in the details from my textbook. (I think they're called in "road maps" in one of those deals that's really popular on here.) basically you just need to be able to give reacants, reagents/conditions, or products if given the other two so just write out each reaction and a couple key notes (i.e. anti addition, etc.). that plus brushing up on nomenclature and stereochemistry (if it's been a while) is all you need.

- for GC, I went through a Chem AP book I had from back in high school and just made sure I could do every type of problem. there's only so many different types of problems that can be repeated to you with different compounds/numbers...

- for Bio, Cliffs AP Bio is your bible. know it cover to cover. that will get you 35/40 on the DAT automatically. the other 5 depends on luck and how good you are at thinking on your feet, but if you already shored up on TS through OC and GC, it won't be much of a hit. you can put in more studying for Bio if you want, but nothing short of A's in genetics, molec cell, micro, immuno, ..., etc. and a bear-trap memory is going to protect you from the randomness so it really isn't worth your time to go beyond Cliffs. if you have time, the bang for your buck is in making sure you're absolutely bullet proof on the chemistry sections.

- for QR, I didn't study...like I've said before it boggles my mind that this is such a notorious section because it's middle school and high school level math. what you have working in your favor is that the questions basically get recycled with different shapes, numbers, etc. so if you've done enough of them you'll be fine. if you're not a QR natural do as many probs as possible, and make sure to get good explanations on everything. hit up the forums if you need to and I'll be happy to help.

- for PAT...CDP. period. do those ten tests over and over until you average 2-3 points above where you want to score and you'll get it. i had a few tricks on each of the sections but all that info is already all over sdn. find what works for you and just hone in on it.

- for RC just know that everything has to be substantiated in the passage. no matter if it's a simple recall question or an inference you should be able to scroll up and find exact sentence(s) that prove you have the right answer. that's if you're a fast reader. if not, god have mercy on your soul. i don't know what to tell you in that case haha.

I know this is rough...maybe I'll try to polish it up later. feel free to PM me if any of you have questions. also, I know you need a subscription to get that full-text for the OC link I put up there. chances are you can get it through your school's library log-in but if not hit me up and i'll see if I can get you a copy of the PDF.

peace and good luck to you.

 

[Josh779]

for sure the way to attack TS is to lockdown GC and OC:

- for OC I used this (http://pubs.acs.org/doi/abs/10.1021/ed084p1224) as the master plan of what the study and filled in the details from my textbook. (I think they're called in "road maps" in one of those deals that's really popular on here.) basically you just need to be able to give reacants, reagents/conditions, or products if given the other two so just write out each reaction and a couple key notes (i.e. anti addition, etc.). that plus brushing up on nomenclature and stereochemistry (if it's been a while) is all you need.

- for GC, I went through a Chem AP book I had from back in high school and just made sure I could do every type of problem. there's only so many different types of problems that can be repeated to you with different compounds/numbers...

- for Bio, Cliffs AP Bio is your bible. know it cover to cover. that will get you 35/40 on the DAT automatically. the other 5 depends on luck and how good you are at thinking on your feet, but if you already shored up on TS through OC and GC, it won't be much of a hit. you can put in more studying for Bio if you want, but nothing short of A's in genetics, molec cell, micro, immuno, ..., etc. and a bear-trap memory is going to protect you from the randomness so it really isn't worth your time to go beyond Cliffs. if you have time, the bang for your buck is in making sure you're absolutely bullet proof on the chemistry sections.

- for QR, I didn't study...like I've said before it boggles my mind that this is such a notorious section because it's middle school and high school level math. what you have working in your favor is that the questions basically get recycled with different shapes, numbers, etc. so if you've done enough of them you'll be fine. if you're not a QR natural do as many probs as possible, and make sure to get good explanations on everything. hit up the forums if you need to and I'll be happy to help.

- for PAT...CDP. period. do those ten tests over and over until you average 2-3 points above where you want to score and you'll get it. i had a few tricks on each of the sections but all that info is already all over sdn. find what works for you and just hone in on it.

- for RC just know that everything has to be substantiated in the passage. no matter if it's a simple recall question or an inference you should be able to scroll up and find exact sentence(s) that prove you have the right answer. that's if you're a fast reader. if not, god have mercy on your soul. i don't know what to tell you in that case haha.

I know this is rough...maybe I'll try to polish it up later. feel free to PM me if any of you have questions. also, I know you need a subscription to get that full-text for the OC link I put up there. chances are you can get it through your school's library log-in but if not hit me up and i'll see if I can get you a copy of the PDF.

peace and good luck to you.

Wow those are insane scores, but it seems like you teach these subjects so it makes sense. I know destroyer has been talked to death on this forum, but what is your opinion on it? I take my DAT on July 12th and did pretty much what you said with the chems. I have gone through the chemistry sections a couple of times. Is this sufficient for these subjects? I want 24+

 

[rockclock]

Wow those are insane scores, but it seems like you teach these subjects so it makes sense. I know destroyer has been talked to death on this forum, but what is your opinion on it? I take my DAT on July 12th and did pretty much what you said with the chems. I have gone through the chemistry sections a couple of times. Is this sufficient for these subjects? I want 24+

I've never seen/done destroyer...seemed like a rip-off to me when I was studying since it costs so much and it looks like such a rickety one-man operation (I remember seeing that website haha) but people seem to have very good things to say about it.

Since you still have ten days I'd track down a Chem AP book from a high school library or something like that. If you're already well-prepared you should literally be able to look through the problems and know that you could do them without actually putting pen to paper or running the numbers. It would be maybe 2-3 hours one afternoon, but if you pass that heat check you know you're golden.

For OC, if you can get your hands on that reaction map I linked to and do the same thing (i.e. look each reaction over and know to yourself that you would have recognized it) then you should be good. of course, half the questions are basic nomenclature, stereochem, SN1/SN2/E1/E2 (first semester stuff) so also make sure that you're not taking any of those freebies for granted by studying reactions only and glossing over some minor detail here or there.

I only say those two things because you still have a good week plus...just going off what others have said about destroyer though, my gut reaction is that you're already in good shape. good luck! looking forward to a solid breakdown from you

 

[Josh779]

I've never seen/done destroyer...seemed like a rip-off to me when I was studying since it costs so much and it looks like such a rickety one-man operation (I remember seeing that website haha) but people seem to have very good things to say about it.

Since you still have ten days I'd track down a Chem AP book from a high school library or something like that. If you're already well-prepared you should literally be able to look through the problems and know that you could do them without actually putting pen to paper or running the numbers. It would be maybe 2-3 hours one afternoon, but if you pass that heat check you know you're golden.

For OC, if you can get your hands on that reaction map I linked to and do the same thing (i.e. look each reaction over and know to yourself that you would have recognized it) then you should be good. of course, half the questions are basic nomenclature, stereochem, etc. (first half of first semester stuff) so also make sure that you're not taking any of those freebies for granted by studying reactions only and glossing over some minor detail here or there.

I only say those two things because you still have a good week plus...just going off what others have said about destroyer though, my gut reaction is that you're already in good shape. good luck! looking forward to a solid breakdown from you

Thanks man, I will take your advice. Any chance you could pm me the PDF for o-chem?

 

[Troyvdg]

haha thanks yappy, but it's really just that I pick and choose which questions to answer and keep my mouth shut when I don't know what I'm talking about. people getting on these forums and making the situation worse instead of better by giving wrong answers is a huge pet peeve...it's one thing to say that you're just throwing something out there (nothing against what Troyvdg did ), it's another when people build themselves up saying they've tutored, gotten A's, etc. and then spread misinformation...that's usually when I butt heads with those d-bags haha

we learn best from our mistakes , and better here then on the test

 

[demolitionlvr]

Cl- does not "neutralize" H+...HCl is a strong acid and those two ions are going to stay dissociated in solution.

This is your reaction (precipitation):

3Ca^2+ (aq) + 2PO4^3- (aq) --> Ca3(PO4)2 (s)

1 M PO4^3- solution is going to require 1.5 M Ca^2+ if you notice to 3:2 stoichiometric ratio above. That's what the question is asking.

Thank you so much!