Food tests and energy calculations

Which of the following tests for starch?

• Iodine

• Benedicts

• Biuret

• Ethanol

Answer explanation

Iodine is the test that specifically detects starch. When iodine is added to a starch solution, it forms a blue-black complex, indicating the presence of starch. The other options test for different substances.

Which of the following tests for protein?

• Iodine

• Benedicts

• Biuret

• Ethanol

Answer explanation

The Biuret test specifically detects proteins by forming a complex with peptide bonds, resulting in a color change. Iodine tests for starch, Benedict's for reducing sugars, and ethanol for lipids, making Biuret the correct choice.

When protein is present Biuret turns...

• purple

• blue-black

• orange

• blue

Answer explanation

When protein is present, the Biuret reagent reacts and changes color to purple, indicating the presence of peptide bonds. This is a key test for proteins.

When reducing sugar (glucose) is present Benedict's turns...

• purple

• blue-black

• brick-red

• green

Answer explanation

When reducing sugar like glucose is present, Benedict's reagent changes color. The correct result is brick-red, indicating a positive reaction, as it forms a precipitate of copper(I) oxide.

In a negative test for starch, what colour will iodine be?

• yellow-brown

• blue

• black

• blue-black

Answer explanation

In a negative test for starch, iodine does not react with starch and remains its original color, which is yellow-brown. This distinguishes it from positive tests that turn blue-black or black.

A negative test for glucose will cause Benedicts to stay...

• brick red

• blue

• black

• yellow

Answer explanation

A negative test for glucose means no glucose is present. Benedict's solution remains blue in the absence of reducing sugars like glucose, indicating no reaction. Therefore, the correct answer is blue.

If you drop iodine on bread, the iodine turns blue-black. What does this show?

• Bread contains protein

• Bread contains sugar

• Bread contains starch

• Bread contains lipids

Answer explanation

The black color change when iodine is dropped on bread indicates the presence of starch. Iodine reacts with starch to form a blue-black complex, confirming that bread contains starch.

How do you test for lipids?

• By using ethanol

• By using Benedicts solution

• By using iodine

• By using Biuret reagent

Answer explanation

To test for lipids, you use ethanol and water. When lipids are present, a milky emulsion forms after mixing the ethanol solution with water, indicating the presence of fats. Other tests listed are for different substances.

Which food test requires heat?

• Reducing sugar (glucose)

• Protein

• Fat

• Starch

Answer explanation

The reducing sugar test, specifically for glucose, requires heat to facilitate the reaction with Benedict's reagent, which indicates the presence of reducing sugars. Other tests do not require heat.

What would you use to show that a food contains fat?

• Ethanol

• Benedicts solution

• Iodine

• None of these

Answer explanation

Lipids are tested using ethanol, which dissolves fats and forms a cloudy emulsion when mixed with water. Other options like Benedict's solution, iodine, and Biuret test are used for carbohydrates and proteins, not lipids.