biological molecules: testing for carbohydrates

Question 1

what are the 3 types of tests for “testing for carbohydrates”

Answer 1

• benedicts test for reducing / non-reducing sugars
• iodine test for starch
• reagent strips for the prescence of reducing sugars

Question 2

what are reducing sugars

Answer 2

monosaccharides and some disaccharides (maltose and lactose)
they can donate electrons
they can reduce another molecule or chemical

Question 3

what is the chemical test for reducing sugar

Answer 3

benedicts reagent
an alkaline solution of copper 2 sulfate

Question 4

how is the benedicts test for reducing sugars carried out

Answer 4

1. place sample to be tested in boiling tube, if not liquid ,grind or blend it in water
2. add an equal volume of benedicts reagent
   3.heat the mixture gently in a boiling water bath for 5 minutes

Question 5

what is the result of a reducing sugars in the benedicts test

Answer 5

electrons are added to the blue copper2 ions forming brick red copper plus ions (brick red precipitate) - indicating a positive result

Question 6

is the benedicts test for reducing sugars qualitative or quantitative

Answer 6

qualitative
the result depends on the concentration of reducing sugars present

Question 7

how does sucrose (non - reducing sugar) give a positive result for testing for reducing sugars

Answer 7

if sucrose is first boiled with hydrochloric acid
because the sucrose has been hydrolysed by the acid to glucose and fructose which are reducing sugars

Question 8

what is the result for non reducing sugars in the benedicts test

Answer 8

the solution remains blue after being warmed

Question 9

what is the chemical in the test for starch

Answer 9

iodine

Question 10

steps in carrying out the iodine test for starch

Answer 10

few drops of iodine dissolved in potassium iodide solution are mixed with a sample

Question 11

what is the result if starch is present in the iodine test

Answer 11

solution changes colour from yellow/brown to purple/black

Question 12

what is the result if starch is not present in the iodine test

Answer 12

the solution remains yellow / brown

Question 13

what else can be used for the testing of prescence of reducing sugars

Answer 13

raegent strips

Question 14

what is the advantage of using raegent strips

Answer 14

using a colour- coded chart , the concentration of reducing sugars can be determined

Question 15

2 different quantitative methods to determine concentration

Answer 15

colorimetry
biosensors

Question 16

what does a colorimeter do

Answer 16

piece of equipment that measures the absorbance/transmission of light to determine the concentration of a reducing sugar that is present
more concentrated a solution the more light it absorbs so the less light is transmitted