Experiment 3: Chemical Reactions: Pigment Synthesis PDF

Experiment 3 Chemical Reactions: Pigment synthesis Safety and Hazards Wear safety glasses and gloves throughout this experiment Copper sulfate (CuSO4) stains the skin Malachite is a low toxicity pigment Verdigris is toxic by ingestion...

Experiment 3 Chemical Reactions: Pigment synthesis Safety and Hazards Wear safety glasses and gloves throughout this experiment Copper sulfate (CuSO4) stains the skin Malachite is a low toxicity pigment Verdigris is toxic by ingestion and may cause irritation NaOH solutions should be handled with care Glacial acetic acid (100%) is highly corrosive, and it causes severe skin burns and eye damage. You should always use this chemical under a fume hood. Procedure Don’t forget to record all your observations in the lab notebook! Take pictures of all your precipitates. Part 1. Malachite Synthesis 2 CuSO4∙5H2O(aq) + 2Na2CO3(aq) → CuCO3∙Cu(OH)2(s) + 2Na2SO4(aq) + CO2(g) + 9H2O(l) 1. Using a graduated cylinder, measure 30 mL of 10% sodium carbonate (Na2CO3) solution. 2. Prepare a solution of 5.0 g CuSO4 · 5 H2O, copper sulfate pentahydrate, in 25 mL water in a 150-mL (or 250-mL) beaker and stir with a magnetic stir bar on a magnetic stirrer until dissolved. If a few small crystals are left, that is okay. Note: The mass does not have to be exactly 5.0 g, just close. Record the mass. 3. Gradually add carbonate solution to the vigorously stirred copper solution. As soon as a reaction can be observed with evolution of carbon dioxide (bubbling) stop until the foaming subsides. Then add the remaining carbonate solution slowly or the mixture will spill over. 4. Heat the reaction mixture at 220 ℃ settings for 20 min. Make sure your reaction is stirring! You must see a green-blue precipitate. 5. Remove the stir bar and allow the mixture to cool down to room temperature before leaving it in an ice bath for about 10-15 min. 6. Turn off the hot plate to cool it down before the next synthesis. While waiting you can start weighing reagents for the second part of the lab (Verdigris Synthesis). 7. Filter by vacuum filtration. connect to vacuum 8. Add distilled water to collect the solid sticking to the beaker’s walls and pour over the solid in the funnel. 9. Maintain suction for about 10 minutes. 10. Transfer the product onto a labelled dry and clean watch glass. To help complete the drying process, press the crystals with a paper towel. Place the watch glass with the precipitate in the drying oven for around 1h. 11. Empty the vacuum flask into the sink and rinse it. Proceed with verdigris synthesis. 12. Weigh the resulting dry product and record the mass. Take a picture of the product. Part 2: Synthesis of Verdigris First step: CuSO4·5H2O(aq) + 4 NH3(aq) → [Cu(NH3)4]SO4(aq) + 5 H2O(l) 1. Weigh out about 2.50 g CuSO4·5H2O and transfer to a beaker. Add 25 mL of distilled water and stir on a magnetic stirrer with a magnetic stir bar until the copper salt has dissolved. Continue to stir the solution vigorously. 2. Add dropwise about 20-30 mL of 10% ammonia solution. When a drop of ammonia touches the liquid surface, you will see the deep blue colour of the copper ammonium complex, [Cu(NH3)4]2+, which disappears after mixing. The dropwise addition of ammonia solution is continued until the intense blue color remains throughout the reaction mixture. Second step: [Cu(NH3)4]SO4(aq) + 2 NaOH (aq) → Cu(OH)2(s) + Na2SO4(aq) + 4 NH3(aq) 3. To the reaction mixture, pour rapidly 15 mL of 2.0 M sodium hydroxide to precipitate copper(II) hydroxide, Cu(OH)2. Stir the mixture for an additional 5 min. connect to vacuum 4. Pour the contents of the beaker into the Buchner funnel. Use a wash bottle to wash out all Cu(OH)2 from the beaker and wash the solid in the funnel with a few mL of water. Then wash the precipitate with about 5 mL of 95% ethanol. Maintain suction for about 5 minutes. Make sure it is dry. If you have water left, use more ethanol. 5. Empty the vacuum flask into the waste bottle in the fume hood. Rinse it with distilled water. 6. Take a picture of the precipitate Third step: Cu(OH)2(s) + 2 CH3COOH(l) → Cu(CH3COO)2(s) + 2 H2O(l) 7. Carefully place the filter paper with the precipitate on an absorbent paper towel with another paper towel on top of the damp solid to absorb as much water as you can. 8. In the fume hood, measure 10 mL of glacial acetic acid using a cylinder and add into a 100-mL beaker. Remove the solid Cu(OH)2 from the filter paper, add to the beaker with acetic acid and stir. Stir the reaction mixture for 10 to 15 min, ensuring that all the copper(II) hydroxide comes into contact with the acid. connect to vacuum 9. Filter the precipitate by vacuum filtration under the fume hood, rinse. Don’t use water! You will dissolve the product. 10. Rinse with a small amount of glacial acetic acid. 11. Empty the vacuum flask into the waste bottle in the fume hood. Rinse it with distilled water. 12. Weigh the watching glass and transfer the product. Leave the precipitate in the fume hood to dry and measure the mass. 13. Take a picture of the product. 2