General Chem Question

[krnkimsung]

Hi everyone,

could someone please help me with the explanation?

1) Which of the following pairs of compounds could be mixed to produce a buffer solution?

a. CH3NH3I and HI
b. CH3NH2 and CH3NH3I
c. CH3NH3 and NH4I
d. HI and NH4I
e. CH3NH2 and NH3

--> Correct answer is "(B)"

Thanks,

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[mrdorky]

First off you got to ask yourself what is a buffer solution?

Basically an aq solution consisting of Weak Base and it's Conjugate Acid, or
Weak Acid and it's Conjugate Base.
So first start eliminating.

you can eliminate the Strong Acids such as A and D which contain HI.
choice E has two Weak Bases so eliminate.
Between B and C
B is the answer because CH3NH2 is a weak base. CH3NH3I (the salt of either the weak base or weak acid is always coupled to a an anion or cation depending on if its a base or acid)
will hydrolize to CH3NH3+ [the conjugate acid of that weak base] and I- in solution.