IDENTIFYING MACROMOLECULES

Indicators In this lab, you will use indicators as chemical detection tool. Indicator- something that can be used to show if a substance is present in a solution. Detection is based upon observing a chemical change; most often a change in color.

Indicators Indicators are chemical compounds used to detect the presence of other compounds. Indicators are chemical compounds used to detect the presence of other compounds.

Background Information INDICATORMACRO-MOLECULENEGATIVE TESTPOSITIVE TEST Glucose stripsSimple carbohydrate Benedict’s solutionsimple carbohydrate Iodine solutioncomplex carbohydrate Biuret solutionprotein Sudan IVlipid Paper Towellipid

Test for Simple Carbohydrates Glucose Strips Small disposable strips of plastic, with an indictor on the end, used to detect simple sugars such as glucose: C 6 H 12 O 6. Aqua blue: negative test; Green to brown: positive test Positive Negative

Test for Simple Carbohydrates Benedict’s solution Benedict's solution is a chemical indicator for simple sugars such as glucose: C 6 H 12 O 6. Aqua blue: negative test; Yellow/green/brick red, etc.: positive test Positive Negative

Test for Simple Carbohydrates Benedict’s solution it must be heated first. Unlike some other indicators, Benedict’s solution does not work at room temperature - it must be heated first.

DEMO

Test for Complex Carbohydrates Iodine solution Iodine solution is an indicator for a molecule called starch. Starch is a huge molecule made up of hundreds of simple sugar molecules (such as glucose) connected to each other.

Test for Complex Carbohydrates Iodine Solution Iodine solution  color change = blue to black (positive)

DEMO

Question: Benedict’s Solution Why didn’t the test tube containing sucrose change colors?

Question Benedict’s Solution Why didn’t the test tube containing starch change colors?

Benedict’s Test Benedict’s reagent undergoes a complex colour change The intensity of the colour change is proportional to the concentration of sugar present The colour change sequence is: – Blue… no sugar – green… very little sugar – yellow…little sugar – orange…sugar – brick red...high sugar concentration

Test for Protein (amino acids) Indicator is Biuret solution Biuret solution  dark violet blue to pinkish purple (positive)

DEMO

Test for Fats (lipids) Sudan IV If lipids are present the Sudan IV will stain them reddish-orange (positive test). Positive Negative

Test for Fats (lipids) Paper Towel Test If lipids are present they will not evaporate on a paper towel as compared to water.

DEMO

Background Information INDICATOR MACRO- MOLECULE NEGATIVE TEST POSITIVE TEST Glucose Strips simple carbohydrate Aqua blue (pale blue) Green to Brown color Benedict’s solution simple carbohydrate Pale blue Red, yellow, orange, green Iodine solution complex carbohydrate Yellow- brown- dark red Purple, black Biuret solutionproteinAqua blue violet, dark blue Sudan IVlipidClear- pale redRed Paper TowellipidEvaporatesRemains Present