Untitled Deck

Question 2

What type of tests are carried out to determine if a sample contains sugars?

Answer 2

Qualitative tests

These tests do not provide quantitative values for the amount of sugar present.

Question 3

How are sugars classified?

Answer 3

Reducing or non-reducing

This classification is based on their ability to donate electrons.

Question 4

What does OILRIG stand for in Chemistry?

Answer 4

Oxidation Is Loss, Reduction Is Gain

This acronym helps in remembering the electron transfer process.

Question 5

What is Benedict’s reagent?

Answer 5

A blue solution containing copper (II) sulfate ions (CuSO4)

It is used in the Benedict’s test for reducing sugars.

Question 6

What forms when a reducing sugar is present in the Benedict’s test?

Answer 6

Copper (I) oxide precipitate

Copper (I) oxide is insoluble in water.

Question 7

What is the method for carrying out the Benedict’s test?

Answer 7

Add Benedict’s reagent to a sample, heat in a water bath, observe for a color change

A positive result indicates the presence of reducing sugars.

Question 8

What indicates a positive result in the Benedict’s test?

Answer 8

A color change from blue to a range of colors including green, yellow, orange, or brown/brick-red

This indicates varying concentrations of reducing sugar.

Question 9

What is the key non-reducing sugar mentioned?

Answer 9

Sucrose

It is the only non-reducing sugar that is specifically noted.

Question 10

What is the first step in testing for non-reducing sugars?

Answer 10

Add dilute hydrochloric acid and heat in a water bath

This hydrolyzes glycosidic bonds in carbohydrate molecules.

Question 11

What is used to neutralize the solution after adding hydrochloric acid?

Answer 11

Sodium hydrogencarbonate

This ensures the solution is slightly alkaline for the Benedict’s test.

Question 12

How is a starch test performed?

Answer 12

Add a few drops of orange/brown iodine in potassium iodide solution to the sample

A blue-black color indicates the presence of starch.

Question 13

What color indicates the presence of starch in a sample?

Answer 13

Blue-black

This color results from the interaction of iodide ions with starch molecules.

Question 14

What does the addition of acid do in the non-reducing sugar test?

Answer 14

Hydrolyzes glycosidic bonds

This results in monosaccharides that can donate electrons.

Question 16

What are the five biological molecules that can be tested for in food?

Answer 16

• Reducing sugars
• Non-reducing sugars
• Proteins
• Starch
• Lipids (fats and oils)

These molecules are essential for understanding food composition and nutritional content.

Question 17

What reagent is used to test for reducing sugars?

Answer 17

Benedict’s reagent

A color change indicates the presence of reducing sugars.

Question 18

What is the method for testing reducing sugars?

Answer 18

1. Add 2cm3 of test solution and Benedict’s reagent to a boiling tube.
2. Heat in a boiling water bath (80°C or higher) for five minutes.
3. Observe the color of the precipitate formed.

The color change can indicate the amount of reducing sugar present.

Question 19

What is the first step in testing for non-reducing sugars?

Answer 19

Test the solution for the presence of reducing sugars.

If no color change is observed, further steps are needed.

Question 20

What is added to hydrolyze non-reducing sugars during the testing process?

Answer 20

Hydrochloric acid

HCl breaks glycosidic bonds, releasing reducing sugars.

Question 21

What must be done after adding hydrochloric acid in the non-reducing sugars test?

Answer 21

Heat the boiling tube in a water bath (80°C or higher) for two minutes and then allow to cool.

This is crucial for the hydrolysis to occur.

Question 22

What reagent is used to test for proteins?

Answer 22

Biuret reagent

A color change indicates the presence of proteins.

Question 23

What is the expected color change when testing for proteins?

Answer 23

Pale blue to purple

The intensity of the purple color can indicate protein concentration.

Question 24

What is the method for testing starch?

Answer 24

1. Add 2 cm3 of test solution to a test tube.
2. Add two drops of iodine-KI reagent and gently mix.
3. Record observations.

The color change indicates the presence of starch.

Question 25

What color change indicates the presence of starch?

Answer 25

Yellow-brown to blue-black (amylose) or red-purple (amylopectin)

Different forms of starch can produce different colors.

Question 26

What is the method for testing lipids?

Answer 26

1. Add 2 cm3 of test solution to a test tube.
2. Add 5 cm3 of ethanol and shake.
3. Allow the mixture to settle.
4. Pour into a boiling tube half-filled with distilled water.
5. Record observations.

A white, cloudy emulsion indicates the presence of lipids.

Question 27

What is the expected result when testing for lipids?

Answer 27

White, cloudy emulsion forms

This indicates the presence of fats or oils.

Question 28

What is a precaution when handling hydrochloric acid?

Answer 28

Wear gloves when handling HCl

This helps prevent skin irritation.

Question 29

True or False: Benedict’s reagent is used to test for both reducing and non-reducing sugars.

Answer 29

True

Different protocols are followed for each type of sugar.

Question 30

Fill in the blank: To test for starch, add two drops of _______ reagent.

Answer 30

iodine-KI

This reagent specifically reacts with starch.

Question 31

What personal protective equipment should be worn when handling Biuret reagent?

Answer 31

Safety goggles and gloves

This is to prevent irritation and corrosion.

Question 32

What is the risk associated with ethanol during food tests?

Answer 32

Highly flammable

Precautions should be taken to avoid fire hazards.