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Pure water at 100 °C has a pH of 6.14 - VCE - SSCE Chemistry - Question 6 - 2012 - Paper 1
Question 6
Pure water at 100 °C has a pH of 6.14. This is because A. the self-ionisation of water is endothermic. B. pH measurements at this temperature are unreliable. C. pH m... show full transcript
Worked Solution & Example Answer:Pure water at 100 °C has a pH of 6.14 - VCE - SSCE Chemistry - Question 6 - 2012 - Paper 1
Step 1
Step 2
B. pH measurements at this temperature are unreliable.
Answer
This statement is accurate. At elevated temperatures, particularly at boiling point, pH measurements can be affected by various factors including changes in ion activity and the presence of dissolved gases. Therefore, this is the most plausible option that explains why the pH of pure water at 100 °C is measured at 6.14.
Step 3
C. pH measurements are affected by the bubbles of hydrogen gas that form in boiling water.
Answer
This statement is misleading. While bubbles may occur during boiling, the actual pH value is not directly affected by physical bubbles; thus, this does not provide a strong rationale for the pH measurement.
Step 4
D. the concentration of H₂O⁺ ions is not equal to the concentration of OH⁻ ions at this temperature.
Answer
At 100 °C, the ion product of water ( K_w = [H⁺][OH⁻] ) does change, leading to unequal concentrations of H₂O⁺ and OH⁻ ions, but this still does not directly provide a reliable explanation for the specific pH measurement.