Question 1
Which of the following combinations cannot be used to produce a buffer solution?
and
and
and
and
Explanation: Buffer solutions can be made via two methods. The first method involves adding equal amounts of a weak acid and a salt of its weak conjugate base (or vice versa). The second methods involves adding a weak acid and a half equivalent of a strong base (or vice versa).
is a weak acid and 
is a salt of its weak conjugate base; therefore, this can form a buffer.
is a weak base and 
is a salt of its weak conjugate acid; this can also form a buffer. Note that this is the converse of the first method (weak base with salt of weak acid), but it can still form a buffer solution.
is a strong acid and 
is a weak base; therefore, adding 
and a half equivalent of 
will create a buffer solution. This is the converse of the second method (adding a weak base to a half equivalent of strong acid).
and 
are both strong reagents (acid and base, respectively); therefore, they cannot form a buffer solution.
is a weak acid and is a salt of its weak conjugate base; therefore, this can form a buffer.
is a weak base and is a salt of its weak conjugate acid; this can also form a buffer. Note that this is the converse of the first method (weak base with salt of weak acid), but it can still form a buffer solution.
is a strong acid and is a weak base; therefore, adding and a half equivalent of will create a buffer solution. This is the converse of the second method (adding a weak base to a half equivalent of strong acid).
and are both strong reagents (acid and base, respectively); therefore, they cannot form a buffer solution.