The dissociation constant of propanoic acid (HC_3H_5O_2) is 1.3 times 10^-5. Wha
ID: 1054086 • Letter: T
Question
The dissociation constant of propanoic acid (HC_3H_5O_2) is 1.3 times 10^-5. What is the pH of a buffer made with 0.50 M propanoic acid and 0.25 M NaC_3H_5O_2 (the sodium salt of propanoic acid)? 4.59 5.19 7.00 I'm not getting any of these answers. A certain chemical reaction runs very slow at high pH values and very fast at lower ph values. To study the reaction, a chemist needs to buffer the solution at a basic pH. What would be the pH of a buffer solution that had the following concentrations: 0.42 M NH_4Cl and 0.75 M NH_3; K_b of NH_3 = 1.8 times 10^-5 at 25 degree C. 9.00 4.49 9.51 11.57 To culture a certain bacteria a microbiologist would like to buffer the media at a PH of 3.75. To maximize the efficiency of the system a 1:1 ratio of acid to salt will be used. Which of the following acids would make the choice for the buffer? Acetic acid; K_a = 1.8 times 10^-5 Propanoic acid; K_a = 1.3 times 10^-5 Formic acid; K_a = 1.8 times 10^-4 Nitrous acid; K_a = 4.0 times 10^-4Explanation / Answer
To culture a certain bacteria a microbiologist would like to buffer the media at a pH of 3.75. To maximize the efficiency of the system a 1:1 ratio of acid to salt will be used. Which of the following acids would make the best choice for the buffer?
1. Acetic acid; Ka = 1.8 ´ 10–5
2. Propanoic acid; Ka = 1.3 ´ 10–5
3. Formic acid; Ka = 1.8 ´ 10–4----------------answer best choice for the buffer
4. Nitrous acid; Ka = 4.0 ´ 10–4
If the acid:salt ratio is to be 1:1, the pH will equal pKa.
At a pH of 3.75 the closest pKa would be from formic acid: 1.8 ´ 10–4.
==========================================================
A certain chemical reaction runs very slow at high pH values and very fast at lower pH values. To study the reaction, a chemist needs to buffer the solution at a basic pH. Determine the pH of a buffer solution that had the following concentrations: 0.42 M NH4Cl and 0.75 M NH3; Kb of NH3 = 1.8 ´ 10–5 at 25°C.
1. 9.00
2. 4.49
3. 9.51----answer
4. 11.57
Using the Kb value of ammonia allows the calculation of [OH–] with the given NH3 and NH4Cl concentrations.
Assuming that no significant NH4+ comes from the NH3 + H2O reaction, the [OH–] could be approximated via [OH–] = Kb (NH3)/(NH4+);
Plugging values in above equation
the pH can then be determined from the pOH.
=====================================================
4. The dissociation constant of propanoic acid and Propanoic acid (HC3Hs0, is 1.3 x 10^-5
What is the pH of a buffer made with 0.50 M propanoic acid AND 0.25 m
NaC3H502 (the sodium salt of propanoic acid),
4.59-answer
5.19
7.00
. I'm not getting any of these answers
Ka = [H3O+ * [CH3CH2COO-] ÷ [CH3CH2COOH]
1.3 * 10^-5 = x * x ÷ (0.5 – x)
multiply both sides by (0.5 – x)
(0.5 – x) * 1.3 * 10^-5 = x^2
0.65 * 10^-7 – 1.3 * 10^-5 x = x^2
x^2 + 1.3 * 10^-5 x – 0.65 * 10^-7 = 0
solving quadratic equation for x
pH = = 4.59
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.