Worksheet: The Chemistry of Food

In this worksheet, we will practice describing how to carry out chemical tests on food for the presence of sugars, starch, protein and fats.

Q1:

A sample is tested with iodine. What is the color change that will occur if the sample contains starch?

  • ABlue-black to brown
  • BPale blue to purple
  • CBrown to brick red
  • DBrown to blue-black
  • EBrown to cloudy white precipitate

Q2:

Complete the table to show the correct biological molecule being tested for, or the name of the test.

Molecule Being Tested for Starch2Protein4
Name of Reagent/Test1Ethanol/Emulsion test 3Benedict’s solution
  • A1: Iodine, 2: Sugars, 3: Biuret, 4: Lipids
  • B1: Biuret, 2: Sugars, 3: Iodine, 4: Carbohydrates
  • C1: Iodine, 2: Lipids, 3: Biuret, 4: Sugars
  • D1: Biuret, 2: Lipids, 3: Iodine, 4: Sugars
  • E1: Biuret, 2: Sugars, 3: Iodine, 4: Lipids

Q3:

A sample is tested using the emulsion test with ethanol. What will the result be if the sample contains lipids?

  • AA purple solution
  • BA layer of cloudy white emulsion
  • CA blue-black solution
  • DA brick-red precipitate
  • EA pale blue solution

Q4:

A banana was tested for different food groups and the results are shown below.

Reagent Added/Test PerformedIodineBenedict’sBiuret
ResultBlue blackBrick redLight purple

Which of the following is the correct conclusion about the biological molecules found in the banana?

  • AThe banana contains starch, sugar, and some protein.
  • BThe banana contains starch and sugar but no protein.
  • CThe banana contains neither starch, sugar, nor protein.
  • DThe banana contains starch but neither sugar nor protein.

Q5:

Proteins are polymers. What monomers are they made from?

  • AFatty acids
  • BGlycerol
  • CSugars
  • DAmino acids

Q6:

An egg yolk was tested for different food groups and the results are provided.

Reagent Added/Test PerformedIodineBenedict’sBiuretEmulsion
ResultOrangeBluePurpleWhite emulsion layer

According to these results, which of the following is the correct conclusion about the biological molecules found in the egg yolk?

  • AThe egg yolk contains sugars and starch, but not protein.
  • BThe egg yolk contains fats and proteins, but neither starch nor sugars.
  • CThe egg yolk contains starch, sugars, protein, and fats.
  • DThe egg yolk contains sugars and proteins, but neither starch nor fats.

Q7:

Two samples of food have been tested with the emulsion test. What are the biological molecules contained in sample Y, according to the demonstrated results?

  • AReducing sugars
  • BProtein
  • CLipids
  • DStarch

Q8:

Complete the statements to correctly describe the composition of the biological molecules.

A protein is made of many monomers called .

  • Afatty acids
  • Bamino acids
  • Cglycerols
  • Dsugars

Many sugar molecules, like glucose, join together to form .

  • Aproteins
  • Bcarbohydrates
  • Clipids

A basic lipid molecule is formed of one and three fatty acids.

  • Aglycogen
  • Bglucose
  • Cglycerol
  • Damino acid

Q9:

When carrying out the test for reducing sugars using Benedict’s reagent, the mixture should be heated in a water bath. Why should a water bath be used, rather than a Bunsen burner?

  • AIt is too dangerous to use a Bunsen burner near Benedict’s reagent.
  • BA Bunsen burner should only be used to heat up water, not other mixtures.
  • CIt is easier to maintain a constant temperature when using a water bath.
  • DA Bunsen burner will not reach the required 75C to heat the mixture.
  • EThis is incorrect; a Bunsen burner should be used.

Q10:

Carbohydrates are polymers. What monomers are they made from?

  • AGlycerol
  • BAmino acids
  • CSimple sugars
  • DFatty acids

Q11:

Benedict’s solution is used to test samples for the presence of sugars. The results from multiple tests are shown in the diagram given.

Which sample has a high proportion of reducing sugars?

  • AY
  • BZ
  • CX
  • DNone of the samples

Which sample has small traces of reducing sugars?

  • AY
  • BZ
  • CX
  • DNone of the samples

Q12:

Two samples of food have been tested with the biuret test. What is the biological molecule contained in sample Y, according to the demonstrated results?

  • AReducing sugars
  • BStarch
  • CProtein
  • DFats

Q13:

A sample is tested using the biuret test. What color change will occur if protein is present in the sample?

  • APale blue to purple
  • BPale blue to white emulsion
  • CPurple to pale blue
  • DPurple to brick red
  • EPale blue to brick red

Q14:

A cookie was tested for different food groups and the results are shown below.

Reagent Added/Test PerformedIodineEthanolBiuret
ResultBlue blackWhite emulsionBlue

Which of the following is the correct conclusion about the biological molecules found in the cookie?

  • AThe cookie does not contain starch, fats, or proteins.
  • BThe cookie contains starch and fats, but not protein.
  • CThe cookie contains neither starch nor fats, but some protein.
  • DThe cookie contains fats, but neither starch nor protein.

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