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Tracking Vitamin C in Pressed Apple Juice 5 questions

Tracking Vitamin C in Pressed Apple Juice

Base your answers on the information provided and your knowledge of chemistry. Use the 2025 Chemistry Reference Tables as needed.

A school orchard presses apples and tests equal portions of the juice. The class uses an iodine indicator model. As long as vitamin C remains, it changes added iodine, I2, into iodide ions, I-. Once the vitamin C is used up, the first excess iodine makes a blue color with starch. In this simplified model, no other juice component uses up iodine.

I2 + 2e- → 2I-

Question 1

Explain why vitamin C is oxidized in the model even though the displayed half-reaction shows a reduction.

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Question 2

Which interpretation fits the first blue color?

  1. Iodide ions have stopped forming because all the starch has been consumed.
  2. Excess iodine is present because the vitamin C has been used up.
  3. All the iodine has been reduced and excess vitamin C remains.
  4. The juice forms new vitamin C after the starch is added.

The class tests one portion of freshly pressed juice and two portions after one day in closed bottles. The two stored portions started with equal volumes of juice and air above it. Only the storage temperature differed. Each iodine amount in the table is corrected to exclude the small excess that produced the blue color.

Equal juice portionCorrected iodine used (µmol)
Freshly pressed8.0
Stored cool7.2
Stored warm5.6

Vitamin C oxidation: C6H8O6 → C6H6O6 + 2H+ + 2e-

Question 3

Use both half-reactions to determine how many micromoles of vitamin C the warm portion contained when tested. Show the mole ratio.

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Question 4

A student says the warm portion kept less than half as much vitamin C as the freshly pressed portion. Use the data to evaluate the claim.

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Question 5

The class wants to test whether the amount of air above the juice affects how much vitamin C remains. Describe what to vary and what to compare while keeping storage temperature and duration the same.

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