DAT Acheiver Gchem question

[nickatina]

I am confused how you figure out if a salt will make a solution acidic or basic. I am referring to question 23 of the gchem which says "Which salt will form a solution with a pH less than 7?"
A) KBr
B) NH4NO3
C)NaF
D)KCN
E)Na2CO3

I understand B through E but I dont really understand why KBr is neutral. It says they are both spectator ions. How would I figure that out?

The supplemental questions are giving me a hard time
A) LiBr
B) FeCl3
C) AlCl3
D)CH3COOK

with these i am having trouble wiht A, B, and C. Can someone explain how to figure out these kinds of problems?

I dont post much on here, but I definitely have been reading these forums for a long time. Now its DAT Crunch time!

Thanks!

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[Dr. juju]

I am confused how you figure out if a salt will make a solution acidic or basic. I am referring to question 23 of the gchem which says "Which salt will form a solution with a pH less than 7?"
A) KBr
B) NH4NO3
C)NaF
D)KCN
E)Na2CO3

I understand B through E but I dont really understand why KBr is neutral. It says they are both spectator ions. How would I figure that out?

The supplemental questions are giving me a hard time
A) LiBr
B) FeCl3
C) AlCl3
D)CH3COOK

with these i am having trouble wiht A, B, and C. Can someone explain how to figure out these kinds of problems?

I dont post much on here, but I definitely have been reading these forums for a long time. Now its DAT Crunch time!

Thanks!

for the first question, react KBr with water, you get KOH + HBr. both are strong base and strong acid respectively. that's why it's neutral.
by the way, is the answer B? (which test is this on, I never saw it?)

for these type of problems, you need to react them with water and see what they produce. remember alkali/alkaline earth metals form strong bases with OH and know your strong acids...

hope this helps

 

[nickatina]

yea the answer is B this is from the Dat Destroyer Gchem section. that makes sense i totally didnt consider that KOH and HBr will neutralize eachother. what about the FeCl3 and AlCl3? are Fe(OH)3 and Al(OH)3 weak bases that wouldnt dissociate completely to neutralize the hydrochloric acid produced? Is that why they form acidic solutions?

 

[Dr. juju]

yea the answer is B this is from the Dat Destroyer Gchem section. that makes sense i totally didnt consider that KOH and HBr will neutralize eachother. what about the FeCl3 and AlCl3? are Fe(OH)3 and Al(OH)3 weak bases that wouldnt dissociate completely to neutralize the hydrochloric acid produced? Is that why they form acidic solutions?

I believe they are..
also you need to pay attention to the solubility rules. sometimes one of the species forms a precipitate, so the other one would affect the solution only.
so it was in destroyer, not achiever!!!

 

[nickatina]

yea my bad. after 8 hours of studying i dont even know what im talking about. thanks for the help.

 

[dudewhensmydat]

I am confused how you figure out if a salt will make a solution acidic or basic. I am referring to question 23 of the gchem which says "Which salt will form a solution with a pH less than 7?"
A) KBr
B) NH4NO3
C)NaF
D)KCN
E)Na2CO3

I understand B through E but I dont really understand why KBr is neutral. It says they are both spectator ions. How would I figure that out?

The supplemental questions are giving me a hard time
A) LiBr
B) FeCl3
C) AlCl3
D)CH3COOK

with these i am having trouble wiht A, B, and C. Can someone explain how to figure out these kinds of problems?

I dont post much on here, but I definitely have been reading these forums for a long time. Now its DAT Crunch time!

Thanks!

Yes, for the first question the answer is B. Notice that NH4 and NO3 will dissociate in water as all nitrates are soluble in aqueous solutions. Furthermore, notice that NH4 will be deprotonated by water to make NH3. Moreover, NH3 is a weak base, so its conjugate base, NH4, must be a strong acid, making the solution have a pH < 7.

In terms of solubility rules, just remember that:

1. All silver, lead, and mercury salts are INSOLUBLE in water.
2. Nitrates, acetates, and perchlorates are SOLUBLE in water.
3. All group I and ammonium salts are SOLUBLE in water.

Hope this helps.