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QLDChemistryQuick questions

Unit 3: Equilibrium, acids and redox reactions

Quick questions on Buffer systems and resistance to pH change (QCE Chemistry Unit 3)

5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is composition?
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Two equivalent compositions both produce a buffer:
What is buffer capacity?
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Buffer capacity is the amount of strong acid or base that can be added before the pH changes significantly. It is determined by:
What is q1?
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Define a buffer and explain how it resists pH change on addition of a small amount of strong acid. [3 marks]
What is q2?
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Calculate the pH of a buffer containing 0.150 mol L−10.150 \, \text{mol L}^{-1} NH3\text{NH}_3 and 0.250 mol L−10.250 \, \text{mol L}^{-1} NH4Cl\text{NH}_4 \text{Cl}. pKb(NH3)=4.75\text{p}K_b(\text{NH}_3) = 4.75, so pKa(NH4+)=9.25\text{p}K_a(\text{NH}_4^+) = 9.25. [3 marks]
What is q3?
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A buffer is prepared from acetic acid and sodium acetate. (a) Write equations showing buffer action against added strong acid and strong base. (b) Explain why buffer capacity is highest when [HA]=[A−][\text{HA}] = [\text{A}^-].

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