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Food Tests Predictions Table

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Food Tests Predictions Table

A food-science team is checking seven samples for starch and reducing sugar. Read the safety notes and test key, make predictions, then use the team’s recorded results to answer the questions. These are sample results for analysis; do not taste any laboratory sample.

Test key and safety

Starch test: add a few drops of the starch indicator. An orange-brown solution turns blue-black if starch is present. Reducing sugar test: add Benedict’s solution and warm the sample in a hot-water bath. A blue solution may change through green, yellow or orange to brick-red if reducing sugar is present; the colour gives a rough indication, not an exact amount. Wear eye protection, use small quantities, and follow your teacher’s instructions for heating. Never heat a sealed test tube or taste samples.

Part A: Predict before testing

For each sample below, predict whether starch, reducing sugar, both or neither will be detected. Predictions are your reasoned guesses, so there is no single correct set. Record them in your notebook or in the spaces beside the sample names.

Sample

Your prediction

Water

Fruit juice

Lucozade

Milk

Potato

Bread

Cooked rice

Part B: The team’s results

The team tested fresh portions of each sample. A plus sign means a positive result; a minus sign means no positive result. For iodine, the positive colour was blue-black. For Benedict’s, positive samples changed from blue to green, yellow, orange or brick-red.

Sample

Iodine test

Benedict’s test

Conclusion

Water

Orange-brown (−)

Blue (−)

Neither detected

Fruit juice

Orange-brown (−)

Orange (+)

Reducing sugar detected

Lucozade

Orange-brown (−)

Brick-red (+)

Reducing sugar detected

Milk

Orange-brown (−)

Green (+)

Reducing sugar detected

Potato

Blue-black (+)

Blue (−)

Starch detected

Bread

Blue-black (+)

Blue (−)

Starch detected

Cooked rice

Blue-black (+)

Blue (−)

Starch detected

Part C: Explain the evidence

Use the recorded results rather than your predictions when answering these questions.

1.Which indicator tests for starch: iodine or Benedict’s solution?

Iodine solution
Benedict’s solution
Both indicators

2.What colour change in the iodine test is evidence that a sample contains starch?

3.According to the results, which three samples tested positive for starch?

4.Which samples tested positive for reducing sugar? Give the evidence from the Benedict’s results.

5.Which sample tested positive for neither starch nor reducing sugar?

Water
Bread
Milk
Fruit juice

6.Did any sample test positive for both substances? Use the table to justify your answer.

TrueFalse

7.A classmate says, “Milk contains no sugar because it does not taste as sweet as Lucozade.” Is this a reliable conclusion from the results? Explain.

8.Why should the team use a fresh portion of food for the iodine test and the Benedict’s test?

9.The Benedict’s test on milk changed from blue to green, while Lucozade changed to brick-red. What can you safely infer, and what should you not claim?

10.Choose one sample and compare your prediction with the team’s result. Was it correct? Give one reason your prediction seemed reasonable.