Testing For Sugars

Question 1

What is a reducing sugar

Answer 1

Sugars that can donate electrons or reduce another molecule or compound

Question 2

What is Benedict’s reagent

Answer 2

An alkaline solution of copper (||) sulfate

Question 3

What are the steps for a Benedict’s test

Answer 3

1. Place the sample in a boiling tube. If it is not a liquid grind it up or blend it with water
2. Add an equal volume of Benedict’s reagent
3. Heat the mixture gently using a water bath for 5 minutes

Question 4

What happens in the reaction between Benedict’s reagent and the reducing sugar

Answer 4

The reducing sugars reacts with the cu2+ ions, they gain electrons and are reduced to cu+ ions.

Question 5

What colour are cu2+ ions and cu+ ions

Answer 5

Cu+ ions are red and cu2+ ions are blue

Question 6

Therefore what is a positive Benedict’s test

Answer 6

If the solution turns brick red a reducing sugar is present.

Question 7

What happen as reducing sugar concentration increases

Answer 7

The more reducing sugar present the less blue cu2+ opens are left in the solution, so the actual color would be a mixture of blue cu+ ions and red cu2+ ions.

Question 8

Is the Benedict’s test qualitative or quantitative

Answer 8

It is qualitative

Question 9

What happens if non reducing sugars reacts with Benedict’s reagent

Answer 9

Nothing, it will remain blue after heating with the Benedict’s reagent indicating a negative result.

Question 10

How can a reducing sugars reacts produce a positive result

Answer 10

If the reducing sugars reacts is boiled with HCL it will then give a positive result when heated with Benedict’s solution. As it will be broken down into reducing sugars.

Question 11

What is the test for starch

Answer 11

Iodine is used to test for starch. A few drops of iodine dissolved in potassium iodide are added to the solution. If starch is present it goes from brown/yellow to blue/black.

Question 12

What are reagent strips

Answer 12

Manufactured reagent strips can be used to test for the presence of reducing sugars such as glucose.

Question 13

What is an advantage of using reagent strips

Answer 13

They come with a colour chart so the concentration can be worked out.

Question 14

What is a colorimeter

Answer 14

A piece of equipment used to quantitavely measure the absorbence or transmission of a solution.

Question 15

What is the relationship between light transmitted and absorbed and concentration

Answer 15

The more concentrated the solution is the less light transmitted and more light absorbed.

Question 16

What are the steps for using a colorimeter (1-3)

Answer 16

1. Place a filter in the colorimeter
2. The colorimeter is then calibrated using distilled water
3. Benedict’s test is then performed on a wide range of known concentrations of sugar

Question 17

What are the steps for using a colorimeter (4-6)

Answer 17

4. Solutions are filtered to remove precipitate
5. Transmissions or absorbable of each concentration and unknown solution are recorded
6. A calibration curve is plotted and using the value of the unknown solution it’s concentration is calculated