Buffer solutions

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15 Terms

1
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What is a buffer solution?

a system that minimises pH changes on addition of small amounts of an acid or base

2
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How do you prepare a buffer solution? (The 2 ways)

a weak acid and a salt of the weak acid

Excess of a weak acid and a strong alkali

3
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What is an example of forming a buffer solution from a weak acid and salt of the weak acid?

CH3COOH and CH3COONa

4
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How is a buffer solution prepared by partial neutralisation of the weak acid?

adding an aqueous alkali solution such as NaOH to an excess of the weak acid (CH3COOH)

5
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What is the conjugate acid-base pair? What is an example?

HA(aq)/A-(aq)

E.g CH3COOH / CH3COO-

6
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When preparing a buffer solution from a weak acid and its salt, what is the source of the conjugate base component?

the salt: when the salt is added to water, the salt completely dissolves so is the source of the conjugate base component

7
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What happens when an acid is added to the buffer solution_

[H+] increases

H+ ions react with the conjugate base, A-

Equilibrium shifts to the left to remove H+ ions

<p>[H+] increases </p><p>H+ ions react with the conjugate base, A-</p><p>Equilibrium shifts to the left to remove H+ ions </p>
8
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What happens when an alkali is added to the buffer solution?

[OH-] increases

The concentration of H+ ions react with the OH- ions to form H2O

HA dissociates to restore H+ ions

<p>[OH-] increases</p><p>The concentration of H+ ions react with the OH- ions to form H2O</p><p>HA dissociates to restore H+ ions</p>
9
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A buffer is most effective when what?

there are equal concentrations of the weak acid and its conjugate base

10
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When [HA] = [A-], what is true?

pKa = pH

Ka = [H+]

11
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How do you calculate the pH of a buffer solution?

Using Ka

<p>Using Ka</p>
12
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The pH of the blood needs to be maintained between which values?

7.35 - 7.45

13
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The carbonic acid-hydrogencarbonate buffer system operates how when an acid is added?

[H+] increases

H+ ions react with the conjugate base, HCO3-

Equilibrium shifts to the left

<p>[H+] increases</p><p>H+ ions react with the conjugate base, HCO<sub>3</sub>-</p><p>Equilibrium shifts to the left</p>
14
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What happens when an alkali is added to the carbonic acid-hydrogencarbonate buffer system?

[OH-] increases

H+ ions react with OH- ions to form H2O

H2CO3 dissociates so equilibrium shifts to the right

<p>[OH-] increases</p><p>H+ ions react with OH- ions to form H2O</p><p>H<sub>2</sub>CO<sub>3</sub> dissociates so equilibrium shifts to the right </p>
15
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Why does excess of a weak acid and a strong base create a buffer solution?

partial neutralisation of the weak acid

contains both the weak acid and the conjugate base