Gen chem help!!

[flin5845]

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Ok so in the DAT Destroyer 2010 # 69.

Which salt will form a solution with a pH less than 7
A. KBr
B. NH4NO3
C. NaF
D. KCN
E. Na2CO3

From going with what chad said on video 5.3 he said that acidic salts are more soluble in BASIC solutions (pH>7) and basic salts are more soluble in ACIDIC solutions (pH<7)

So when I was working this problems I got the following:

A. Neutral
B. Acidic
C. Basic
D. Basic
E. Basic

Answer is B

I guess I am misunderstanding the question because when I think of "what salt will form a solution with a pH less than 7" I was thinking which salt is most soluble and will form a solution, so I was looking for a basic salt.

I think the question is trying to say "Which salt will form IN a solution with pH less than 7. In this case it would be asking what salt would precipitate if put in an acidic solution.

What am I doing wrong?

 

[herkulease]

Its just asking if these salts were put in water which will get a pH less than 7.

they are all soluble salts and wouldn't form a ppt anyhow.

You could use dr. romano's thing of "crossing"

or chad's thing. I used chad's thing as its just faster.

I don't know what it would be in the newer videos but he had a section dedicated to acidity and basicity of salts. its where you eliminate all the strong bases/acids anions/cations then look at whether the ones are anions and cations and determine the answer.

 

[JustwantDDS]

KBr- cross out K; group 1 negligible cation, cross out Br; negligible anion= NEUTRAL
NH4NO3, cross out NO3, negligible anion, NH4+ left ---> + charge- acidic
NaF- cross out Na, group1 cation, Keep F- --> base
KCN- cross out K, group 1, CN- Base
Na2CO3- cross out Na, keep CO32- - Basic

So the only one left is B thats acidic- which is pH under 7