The Student Room Group

why is the measured ph different to calculated ph

The student calculates the pH of 0.0800moldm−3 HIO3(aq). The student assumes that the
equilibrium concentration of HIO3(aq) is the same as the initial concentration of HIO3(aq).
The student measures the pH, and finds that the measured pH value is different from the
calculated pH value.
Explain why the measured pH is different from the calculated pH.
Original post by Esoteric2
The student calculates the pH of 0.0800moldm−3 HIO3(aq). The student assumes that the
equilibrium concentration of HIO3(aq) is the same as the initial concentration of HIO3(aq).
The student measures the pH, and finds that the measured pH value is different from the
calculated pH value.
Explain why the measured pH is different from the calculated pH.

How many marks is this?

The student is assuming that the HIO3 is a weak acid existing mainly as molecules, but it could be a strong acid therefore dissociating to a much greater extent and so the student’s assumption is wrong. Therefore causing the difference between the measured and calculated pH values.

This may be wrong I’m sorry. Just because I’ve seen no one has answered. I’m Scottish so do a different syllabus, so I’m not sure.
Reply 2
Original post by Esoteric2
The student calculates the pH of 0.0800moldm−3 HIO3(aq). The student assumes that the
equilibrium concentration of HIO3(aq) is the same as the initial concentration of HIO3(aq).
The student measures the pH, and finds that the measured pH value is different from the
calculated pH value.
Explain why the measured pH is different from the calculated pH.


The answer is in the Q "The student assumes that the equilibrium concentration of HIO3(aq) is the same as the initial concentration of HIO3(aq)."

This assumption is incorrect, hence...

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