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Cyanidin is a plant pigment that may be used as a pH indicator - HSC - SSCE Chemistry - Question 20 - 2022 - Paper 1
Question 20
Cyanidin is a plant pigment that may be used as a pH indicator. It has four levels of protonation, each with a different colour, represented by these equilibria: H₃... show full transcript
Worked Solution & Example Answer:Cyanidin is a plant pigment that may be used as a pH indicator - HSC - SSCE Chemistry - Question 20 - 2022 - Paper 1
Step 1
What colour would the indicator be if added to a 0.75 mol L⁻¹ solution of hypoiodous acid, HIO (pKₐ = 10.64)?
Answer
To determine the colour of the indicator in a 0.75 mol L⁻¹ solution of hypoiodous acid, we first note that the pKₐ value of HIO is 10.64. This means that at this pH, we can look at the pH scale and the graph provided to see how the indicator behaves. Since 0.75 mol L⁻¹ of HIO is an acid solution and has a pH significantly below its pKₐ, this would favor the protonated form of the indicator, which corresponds to the colour purple. Therefore, the colour of the indicator in this solution would be:
C. Purple