A) Does the pH increase, decrease or remain the same on the addition of the of t
ID: 954803 • Letter: A
Question
A) Does the pH increase, decrease or remain the same on the addition of the of the following?
LiF to and HF solution
KI to and HI solution
NH4Cl to and NH3 solution
HBr to an CH3COO-/CH3COOH (acetic acid/acetate buffer) solution
Decrease
Remain the same
Increase
B) Which of the following (select all that apply) gives a buffer solution when equal volumes of the two solutions are mixed?
0.10 M HF and 0.10 M NaF
0.10 M HF and 0.10 M NaOH
0.50 M HF and 0.25 M NaOH
0.25 M HCl and 0.50 M NaF
- A. B. C.LiF to and HF solution
- A. B. C.KI to and HI solution
- A. B. C.NH4Cl to and NH3 solution
- A. B. C.HBr to an CH3COO-/CH3COOH (acetic acid/acetate buffer) solution
A.Decrease
B.Remain the same
C.Increase
Explanation / Answer
Question 1.
A) if we add LiF to HF solution, HF is acidic initially, when F- is added, this increase pH to a pKa value, so pH increases.
B) KI to HI has no effect, since this is strong electrolyte fo H+ remains,
C) NH4Cl and NH3 will lower the pH, since NH3 is a base, addition of NH4+ (an acid) will lower pH.
D) HBr is strong acid, by definition, will add H+, therefore decrease pH
Question 2.
A buffer solution must contain: (acid buffer) = weak acid + conjguate base (basic buffer) = weak base + conjguate acid
a) 0.10 M HF and 0.10 M NaF
this is an acidic buffer, since HF and NaF is present
b) 0.10 M HF and 0.10 M NaOH
this is not a buffer, there will be complete neutralization of acid, so only F- is left
c)0.50 M HF and 0.25 M NaOH
this will yield a buffer
0.25 M of HF remains, 0.25 M of F- will form, which is an acidic buffer
d)0.25 M HCl and 0.50 M NaF
this will form a buffer:
0.25 M of NaF will remain as F-
0.25 M of HF will form
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