1. Which of the following aqueous solutions are good buffer systems? 0.24 M hydr
ID: 561516 • Letter: 1
Question
1. Which of the following aqueous solutions are good buffer systems?
0.24 M hydrobromic acid + 0.21 M potassium bromide
0.33 M ammonium bromide + 0.37 M ammonia
0.39 M hydrocyanic acid + 0.23 M potassium cyanide
0.14 M acetic acid + 0.21 M sodium acetate
0.15 M sodium fluoride + 0.23 M hydrofluoric acid
2. Which of the following aqueous solutions are good buffer systems?
0.34 M ammonia + 0.34 M ammonium nitrate
0.16 M barium hydroxide + 0.23 M barium bromide
0.26 M hydrobromic acid + 0.22 M sodium bromide
0.12 M acetic acid + 0.14 M potassium acetate
0.39 M calcium iodide + 0.29 M calcium nitrate
3. A solution contains 0.474 M sodium acetate and 0.434 M acetic acid.
The pH of this solution is ____
4.A solution contains 0.189 M potassium acetate and 0.151 M acetic acid.
The pH of this solution is ____
Explanation / Answer
1.
Answer is 0.14 M acetic acid + 0.21 M sodium acetate
(Since its a weak acid and its conjugated base).
2.
0.12 M acetic acid + 0.14 M potassium acetate
(Since its a weak acid and its conjugated base).
3.
Using Hender-Hesselbalach equation
pH = pKa + log { [salt] / [acid] }
pH = pKa + log { [CH3COONa] / [CH3COOH] }
pKa of CH3COOH = 4.75
So,
pH = 4.75 + log(0.474 / 0.434)
= 4.75 + log(1.09)
= 4.75 + 0.04
= 4.79
4.
Using Hender-Hesselbalach equation
pH = pKa + log { [salt] / [acid] }
pH = pKa + log { [CH3COOK] / [CH3COOH] }
pKa of CH3COOH = 4.75
So,
pH = 4.75 + log(0.189 / 0.151)
= 4.75 + log(1.25)
= 4.75 + 0.10
= 4.85
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