Aldehydes and Ketones 2024 Past Paper PDF

Aldehydes and Ketones Aldehydes and Ketones Goals A. Write the functional groups of aldehydes and ketones. B. Determine chemical and physical properties of Aldehydes and Ketones. C. Perform chemical tests to distinguish between Aldehydes and Ketones. D. Write the formulas of the oxidation...

Aldehydes and Ketones Aldehydes and Ketones Goals A. Write the functional groups of aldehydes and ketones. B. Determine chemical and physical properties of Aldehydes and Ketones. C. Perform chemical tests to distinguish between Aldehydes and Ketones. D. Write the formulas of the oxidation products of Aldehydes. Discussion: A. Structures of Aldehydes and Ketones Aldehydes and ketones are representative of compounds that possess the carbonyl group. Aldehydes have at least one hydrogen attached to the carbonyl carbon; in ketones, no hydrogens are directly attached to the carbonyl carbon, only carbon containing R groups. the aldehyde functional group occurs at the end of the carbon chain. In a ketone, the carbonyl group is located between two of the carbon atoms within the chain. Since they share the carbonyl group, aldehydes and ketones share much of their chemistry, but they are different enough to be considered different classes of compounds. B. Properties of Aldehydes and Ketones Many aldehydes and ketones have sharp odors. If you have taken a biology class, you may have noticed the odor of Formalin, which is a solution of formaldehyde. When you remove fingernail polish, you may notice the strong odor of acetone, the simplest ketone, which is used as the solvent. Aromatic aldehydes have a variety of odors. Benzaldehyde, the simplest aromatic aldehyde, has an odor of almonds.  Aldehydes and Ketones C. Oxidation of Aldehydes and ketones Aldehydes are oxidized to carboxylic acids but, ketones are not. Consequently, Oxidation tests can distinguish between aldehydes and ketones. 1. Chromic Acid Test: (+ve with aldehydes) Aldehydes are oxidized to carboxylic acids by chromic acid; ketones are not oxidized. A positive test results in the formation of a blue-green solution from the brown-red color of chromic acid. 2. Fehling test : (+ve with aldehydes) Aldehydes reduce Fehling's reagent (contains Cu+2; Blue color ) to give orange/red or green precipitate of Cu+1 oxide. 3. Tollens’ Test: (+ve with aldehydes) Aldehydes reduce Tollens’ reagent (ammonia and silver nitrate) to give a precipitate of silver metal. The free silver forms a silver mirror on the sides of the test tube. The aldehyde is oxidized to a carboxylic acid.  Aldehydes and Ketones D. Schiff’s test (+with aldehydes) When Schiff’s reagent adds to an aldehyde solution, a characteristic magenta color develops immediately. E. Iodoform Test: (+ with acetaldehyde and acetone) Methyl ketones (such as acetone), but not other ketones, are oxidized by iodine in aqueous sodium hydroxide to give the yellow precipitate of iodoform when reacted with iodine in aqueous sodium hydroxide. The ketone is oxidized to a carboxylic acid. Acetaldehyde, but not other aldehydes, give this test owing to its structural similarity to methyl ketones. F. Nitroprusside test (+ with acetaldehyde and acetone) Methyl ketones (such as acetone), but not other ketones, as well as Acetaldehyde, but not other aldehydes, react with nitroprusside solution in alkaline condition (sodium hydroxide) to give a purple red color. G. Sodium hydroxide (30%) test (+ with acetaldehyde) When acetaldehyde boiled with sodium hydroxide solution (30%) a yellow aldehyde gum is formed. H. Identification of Unknown The group of tests for aldehydes and ketones described in this experiment will be used to identify the unknown substance.  Aldehydes and Ketones Experimental Procedures A. Properties of Aldehydes and Ketones Materials: test tubes, formaldehyde, acetaldehyde, acetone, benzaldehyde and unknown Odor: A.l Carefully place 0.5 ml of each of sample (formaldehyde, acetaldehyde, acetone, benzaldehyde and unknown) and detect the odor of each. A.2 Draw their condensed structural formulas, You may need a chemistry handbook or a Merck Index. Identify each as a ketone or aldehyde. Solubility in water: Add about 2 mL of water (40 drops) to each test tube. Shake and determine whether each sample is soluble or not. If the substance is soluble in water, you will see a clear solution with no separate layers. If it is insoluble, a cloudy mixture or separate layer will form. Record your observations. B. Chemical tests for Aldehydes and Ketones 1. Oxidation (+with aldehydes) a) Chromic Acid Test Place 0.5ml of the samples in separate test tubes. Carefully add 0.5ml of chromate solution to each. Place in a warm water bath (60oC) for 5 minutes. Look for a color change in the chromate solution. A positive result is indicated by the turns of the orange color to green. If the color remains orange, no reaction has occurred. Record your observations. b) Fehling Test Place 1 ml of freshly prepared Fehling’s solution (made by mixing 0.5 ml Fehling’s solution A and 0.5 ml of Fehling’s solution B) in a test tube. Add 0.5 ml of sample, shake the test tube, then place it in a boiling water-bath for 3-5 minutes and observe the result. A positive result is indicated by the development of precipitate (orange/red or green brown). Negative result is the remaining of blue color. 2. Schiff’s test : (+with aldehydes) Place 0.5ml of the samples in separate test tubes, then add drops of Schiff’s reagent, shake and observe the result. A positive result is indicated by the development of a characteristic magenta color. 3. Iodoform Test (+ with acetaldehyde and acetone) Place 0.5 ml of the each sample in separate test tubes. Add 3 ml of I2/KI solution to each followed by drops of sodium hydroxide solution enough to remove the colour of the iodine.  Aldehydes and Ketones A positive result is the appearance of a very pale yellow precipitate of triiodomethane (CHI3). Also, this can be recognised by its faintly "medical" smell. 4. Nitroprusside test (+ with acetaldehyde and acetone) Place 0.5 ml of sample in a test tube, then add drops of sodium nitroprusside reagent followed by excess (2-3 ml) NaOH 10% shake and observe the result. A positive result is indicated by the development of a purple red color. 5. Sodium hydroxide (30%) test (+ with acetaldehyde) Place 0.5 ml of sample in a test tube, add 2ml of sodium hydroxide 30% shake and then place it in a boiling water-bath for 3-5 minutes and observe the result. A positive result is indicated by the formation of yellow aldehyde gum.  Aldehydes and Ketones Report Sheet – Lab 3 Organic ___________________________________________________________________________ Date_______________________ Name_______________________ I.D.#______________________ Serial #________________________ Group _____________________ Pre-Lab Study Questions 1. What is the functional group of an aldehyde? A ketone? 2. What is the oxidation product of an aldehyde? A. Structures of some Aldehydes and Ketones  Aldehydes and Ketones B. Properties of Aldehydes and Ketones Odor Solubility in Aldehyde or Water? Ketone? Formaldehyde Acetaldehyde Acetone Benzaldehyde C. Chemical tests for Aldehydes and Ketones Formaldehyde Acetaldehyde Acetone Unknown* Chromic acid test Fehling Test Schiff’s test Iodoform test Sodium Nitroprusside test NaOH 30 % *Use the test results to identify your unknown as one of the Three compounds used in this experiment. The Unknown is:--------------------------------------------------------------------------- Aldehydes and Ketones