Post Lab Disc- Carbohydrates, Proteins, and Water Properties, Lecture notes of Chemistry

Download Post Lab Disc- Carbohydrates, Proteins, and Water Properties and more Lecture notes Chemistry in PDF only on Docsity! A C D N P a g e 1 | 7 COLLEGE OF MEDICAL LABORATORY SCIENCE Post Lab Disc- Carbohydrates CARBOHYRATES - Polyhydroxy aldehyde or ketone substances - Compounds containing C, H, O - Functional Groups: C=O or CHO Types of carbohydrates: - Monosaccharides (Glucose and Fructose) - Disaccharides (Lactose, Maltose and Sucrose), and - Oligosaccharides - Polysaccharides (Starch, Glycogen) MOLISCH’S TEST Principle: Carbohydrates when treated with concentrated H2SO4 undergo dehydration to give furfural derivatives. These compounds condense with a-naphthol to form reddish violet colored products. Reagents: - Molisch’s reagent - Concentrated sulfuric acid Result: Purple ring at the junction of 2 layers. A C D N P a g e 2 | 7 BENEDICT’S TEST Principle: They reduce the cupric ions of Benedict’s reagent to red cuprous oxide. The cupric hydroxide formed during the reaction is kept in solution by metal chelators like citrate Reagents: - Benedict’s reagent - Copper sulfate + Sodium carbonate + Sodium Citrate Result: Green- yellow to brown or orange- red or brick red ppt FEHLING’S TEST Principle: The tartarate from Fehling's (B) solution chelates cupric ion, releasing it slowly for reduction thus preventing the formation of black cupric oxide. Reagents: Fehling's Solution Consists of: - Fehling's solution A: - Contains copper sulfate solution. - Fehling's solution B: - Contains potassium hydroxide and sodium potassium tartrate. - Prepare fresh by mixing equal volumes of Fehling's solutions A and B. Result: Green-yellow to brown or orange-red ppt BARFOED’S TEST Principle: Barfoed's test differentiates between reducing monosaccharides and disaccharides. This is a reduction test in acidic medium. Reagents: - Copper acetate - Glacial acetic acid Result: red ppt A C D N P a g e 5 | 7 - 20% sodium carbonate Procedure: - To 5 ml of sucrose solution, add 3 drops concentrated HI and boil for 2 minutes. This will hydrolyze cane sugar to its constituent units glucose and fructose. - Now neutralize the solution with 20% sodium carbonate using red litmus paper as indicator (this is essential as Benedict's test requires alkaline medium). - Boil 1 ml of the neutralized solution with 5 ml Benedict's solution and note the reduction produced. Result: acidic/acid FLOW CHART OF IDENTIFICATION OF UNKNOWN CARBOHYDRATES SOLUTION - Molish's Test A C D N P a g e 6 | 7 POST LABORATORY DISC- PROTEINS PROTEINS - Complex macromolecule made up of amino acids produced by all living cells. - Composed of 20 amino acids varying in numbers and sequence - Amino acids contain both a COOH and an amino group (-NH2) and a side chain (R- group) - Building block: Amino acids - Composed of: CHON. Some of the proteins may contain Sulfur BIURET TEST - General test for proteins. Semi- quantitative. - Will give a positive result for compounds that contains two or more peptide linkages - It will give a distinct purple or violet color which is probably due to the formation of complex cupric ions with amino group called biuret. Principle: Cupric ions in an alkaline medium form a violet colored complex with peptide bond nitrogen of peptides and Proteins. This is a test for peptide linkages. Since all proteins contain peptide linkages, they respond to this test. The violet color is due to the formation of copper coordination complex between cupric hydroxide and peptide bond. Reagents: - 10% NaOH - Copper sulfate Result: - Violet or purple color- presence of 5% albumin (more peptide linkages) - Pink color- presence of peptide linkages (less peptide linkages) - Urea/Alanine- no visible result/ reaction HOPKIN’S COLE TEST Principle: The indole ring of tryptophan combines with aldehydes, e.g formaldehyde in the presence of conc. Sulfuric acid to form a violet-colored compound. Gelatin gives a negative test as it does not contain tryptophan. Reagents: - Hopkin’s Cole Rgt: Formaldehyde + mercuric sulfate + sulfuric acid - Sulfuric acid Result: It forms a separate layer and a deep violet or purple ring forms at the junction of the two layers. 1. Albumin 2. Gelatin 3. Tyrosine - These three have no visible result/ color reaction. - Does not contain tryptophan. - Negative for indole ring. A C D N P a g e 7 | 7 Notes: - Mercuric sulfate cause a mild-oxidation of indole group of tryptophan which condenses with the aldehyde to give a colored complex. POST LABORATORY DISC: WATER & ITS PROPERTIES Solubility - The maximum amount of solute that can be dissolved in a solute at a specific temperature and pressure.