In each trial, you will add an indicator to the mystery food sample. But you will also add the indicator to a known substance and water. Why is that important? Check all reasons.

The known substance provides a positive comparison: it shows what a definite positive result for that indicator looks like. Water provides a negative comparison, showing what a result with no tested food substance looks like. Comparing the mystery sample with both helps you interpret its result; practicing pipette use or simply collecting more data is not the main reason.

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