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The following points provide some background information to assist you in answer...
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The following points provide some background information to assist you in answering this question.
- Buffers are added to foods and beverages to modify flavours and preserve them.
- Cola drinks include phosphoric acid and carbonic acid (from dissolved CO2) that lower the pH of the drink and produce buffer systems.
- The primary buffer system that determines the pH of cola drinks is the phosphoric acid:dihydrogen phosphate (H3PO4/H2PO4-; pK a H3PO4 = 2.16) buffer system.
A range of cola drinks had their pH recorded and were then titrated against 0.05 M NaOH. A summary of the H titration results is shown in the table below.
Table 1. pH of cola drinks vs mL of 0.05 M NaOH added | ||||
Cola Drink | pH of pure Cola Drink | mL to raise pH by 1.0 | mL to raise pH to 5.5 | mL to raise pH to 7.0 |
Coca Cola | 2.7 | 5.19 | 15.00 | 37.93 |
Diet Coke | 3.1 | 5.05 | 16.01 | 49.90 |
Pepsi Cola | 2.5 | 6.35 | 15.43 | 40.67 |
Diet Pepsi | 2.8 | 5.91 | 19.33 | 53.80 |
Selection Cola | 2.7 | 5.05 | 15.58 | 37.64 |
Diet Selection Cola | 3.4 | 5.19 | 16.44 | 48.32 |
- The results show that the drinks Coca Cola and Pepsi Cola have very similar pH values (2.7 and 2.5 respectively)., what does this imply about the composition of their buffer systems? [1 mark]
- For the Coca Cola drink 5.19 mL of 0.05 M NaOH was required to raise the pH by 1.0. However, for the Pepsi Cola drink 6.35 mL of 0.05 M NaOH was required to raise the pH by 1.0. Explain this observation, accounting for your response to the question above and the fact that both cola drinks have the same buffer system. [3 marks]