Chemical Tests And Chromatography

Question 1

What is the test used for proteins called?

Answer 1

Biuret

Question 2

Describe the method used for the biuret test

• include chemicals used
• appearance of positive results

Answer 2

• tests for presence of peptide bonds
• add sample with an equal volume of 10% sodium hydroxide
• add copper sulfate a few drops at a time until solution turns blue
• mix solution and leave for 5 mins
• alkali and copper sulfate solution = biuret reagant
• peptide bonds form violet colour

Question 3

What are reducing sugars

Answer 3

Sugars that donate electrons, resulting in reduction of another molecule

Question 4

What is reduction of a molecule

Answer 4

Gain of electrons

Question 5

What is the test for reducing sugars called

Answer 5

Benedicts

Question 6

Describe the method for benedicts test

• include appearance of negative result
• include appearance of positive result
• include chemicals used

Answer 6

• use a solution of copper II solution (alkaline)
• place sample in boiling tules
• add equal volume of benedicts reagent
• heat in boiling water bath for 5 mins
• reducing sugars react with copper ions
• results in addition of electrons to blue Cu2+ ions, reducing them to red Cu+ ions
• positive result = brick red precipitate
• negative result = blue
• blue -> green -> yellow -> brown -> red

Question 7

What is the test for non reducing sugars

Answer 7

Benedicts

Question 8

Describe the method

• explain positive result
• explain negative result
• describe chemicals used

Answer 8

• carry out normal benedicts test (add reagant to sample, heat)
• negative result - blue
• boil sample with dilute hydrochloric acid
• sugar is hydrolysed to its monomers, which are both reducing sugars
• add benedicts reagent and heat
• positive result = blue -> green -> yellow -> brown -> red

Question 9

What is the test for starch

Answer 9

Iodine

Question 10

Describe the iodine test

• include chemicals used
• describe positive and negative results

Answer 10

• dissolve iodine in potassium iodide

Add a few drops of solution to sample

• positive result = purple / black
• negative result = yellow / brown

Question 11

What is the test for lipids called

Answer 11

Emulsion test

Question 12

Describe emulsion test

• include chemicals used
• describe positive / negative results

Answer 12

• mix sample with ethanol
• mix solution with water and shake
• positive result = white emulsion at tope of solution
• negative = solution remains clear

Question 13

List 4 examples of reducing sugars

Give 1 non reducing sugar

Answer 13

• glucose
• fructose
• maltose
• lactose

1 non reducing sugar
- sucrose

Question 14

What are reagent test strips

Answer 14

Manufactured strips that can be used to test for reducing sugars - mostly glucose

Question 15

Describe how a colorimeter works

Answer 15

• a piece of equipment that quantitively measure absorbance or transmission of light
• the more concentrated, the more light will be absorbed, the less light will be transmitted

Question 16

Describe the purpose of thin layer chromatography

Answer 16

• technique to separate individual components of a mixture

Question 17

Describe a method for using chromatography to identify the components of an unknown mixture of dissolved substances

Answer 17

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