Question

Calculate the theoretical yield for Orange II (mw= 422g/mol; experimental weight of orange II azo-dye=0.4g).

EXPERIMENTAL Calculate the theoretical yield before the lab. Caution: Orange II dyes clothing and other organic materials a permanent unique orange. As a measure of your technique, points may be subtracted for orange hands, etc. 1 DIAZOTIZATION OF SULFANILIC ACID Dissolve 0.4 g of anhydrous sodium carbonate in 7.5 mL of H.O. Use a 25 mL Erlenmever flask. 2. Add 0.45 g of sulfanilic acid to the solution, and heat over a steam bath until it dissolves. 3. Cool the filtrate to room temperature, add 0.2 g of sodium nitrite, and stir until it also dissolves. 4. Pour this pale yellow solution slowly, using a stirring rod, into a 125 mL Erlenmeyer flask con- taining 2 mL of H,O, 1 mL of concentrated HCI (12 M), and about 3 g of ice or enough to just cover the bottom of the flask. 5. In a short time, the diazonium salt of sulfanilic acid may separate as a finely divided white precipitate. 6. Keep this suspension cooled in an ice bath until it is to be used. More ice may be added to the flask if needed; keep a few pieces in the flask at all times. II. ORANGE II 1. Combine 0.38 g of 2-naphthol and 1.6 mL of 10% (2.5 M) sodium hydroxide in a 10 mL pear- shaped flask. 2. Warm over steam to hasten the dissolving (1-2 minutes); then cool briefly in an ice bath (30 seconds). If the sodium salt of 2-naphthol crystallizes, reheat gently to dissolve any solids. 3. Using a dropper, add this solution to the cold suspension of diazotized sulfanilic acid in the 125 ml flask. 4. Stir thoroughly by swirling. In a few minutes, the Orange II will begin to crystallize. 5. Keep the mixture in an ice bath for another 15 minutes to permit the coupling reaction to ap- proach completion. Allow the remaining ice in your mixture to melt. 6. Collect the crude Orange II by suction filtration using a 5.5 cm Büchner funnel. Do not wash this salt with additional water.

Answer 1

experimental weight of dye = 0.4g Molecular weight = 422 guol" for this experiment 2-naphthol 10.38g) was added in the bulk cold suspension of diazolized sulfanulic acid. 2-naphthol will be limiting reagent. I mol of 2-naphthol gives - Imol of orange(4) azo dye Moles of a-naph thol = mass (g) = 0.38g 144.17 gmol Molar mas = 0.00263577 mol Moles of a-naphthol = 0.002636 mol Now I mole of 2-naphthol yolds - imol of orange is on 0.002636 mol willyuild duy Theoretical moles= 0.0026 36 mol of dye Mars of dye = Molex molar mass E.0.002636 mol x 422 ghol - 1.1124 g = Theoretical yield

experimental yilla= ong % yield = experimental yild xico Theoretical yild Doug | 100 = 35.95? Tollaug % yield = 36% Percentage yılld = 367