Consider the next two questions together 27. If hydrochloric acid is added to a
ID: 549910 • Letter: C
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Consider the next two questions together 27. If hydrochloric acid is added to a solution of hydrofluoric acid in water, how will the weak-acid dissociation change? Choices: It will increase It will decrease It will not change 28. To correctly represent the amount of weak-acid dissociation for the hydrofluoric acid after the hydrochloric acid is added, we should use the calculation for the Choices: Degree of ionization, Percent ionization) Fraction of dissociation, the pH, the pOH 9, A buffer is diluted to 25% of its initial strength with water what happens to the buffer capacity? Choices: The buffer capacity will decrease to one-quarter The buffer capacity will decrease to one-half The buffer capacity will increase by adding one-quarter The buffer capacity will increase by adding one-half. The buffer capacity will remain the same as before Consider the next four questions together. 30. A benzoic acid-benzoate buffer contains 0.1158 M benzoic acid and 0.1436 M benzoate ion Calculate the pH of the buffer. Benzoic acid Ka 6.3x10 4,3 31. A benzoic acid-benzoate buffer contains 0.1158 M benzoic acid and 0.1436 M benzoate ion Will the acid buffer capacity or the base buffer capacity be larger? Choices: Acid buffer capacity will be larger, Base buffer capacity be larger, They will be the same, Not enough information to decide 32. A benzoic acid-benzoate buffer contains 0.1158 M benzoic acid and 0.1436 M benzoate ion. A chemist adds 0.0094 mol of HCI to 1.00 L of buffer. Calculate the new pH when the reaction is finished. Benzoic acid K, 6.3x10 4,23 33. A benzoic acid - benzoate buffer contains 0.1158 M benzoic acid and 0.1436 M benzoate ion. A chemist adds 0.0085 mol of NaOH to 2.00 L of buffer. Calculate the new pH when the reaction i finished. Benzoic acid Ka-6.3x10-5 4.35Explanation / Answer
27. Common ion effect: According to this, the dissociation of weak acid decreases further due to the addition of common ion to it.
This in turn depends on the LeChatlier's principle.
Weak acid dissociation forms an equilibrium.
When this system at equilibrium is disturbed by adding a common ion which presents on the right side of the equilibrium ,then the equilibrium will shift towards left side that is undissociated acid is formed.Hence,the dissociation of weak acid decreases further.
28.For this we use percent dissociation.
29.Buffer capacity can be defined as the change in pH per litre of the buffer solution.
It is inversely proportional to the volume of the buffer solution.
Here volume of the buffer solution is increasing,hence the buffer capacity decreases to one quarter .
30.Use Handerson's equation: pH = pKa + log [salt]/[acid]
Substitute the given values in the above equation,then we get:pH= -log(6.3x10-5)+log was
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