Recovery of Elemental Copper from Copper (II) Nitrate

Transcription

1 Recovery of Elemental Copper from Copper (II) Nitrate Objectives: Challenge: Students should be able to - recognize evidence(s) of a chemical change - convert word equations into formula equations - perform a series of chemical reactions in order to recycle the element copper - determine the percent recovery of elemental copper How good and accurate a chemist are you? Given a solution of Cu(NO 3 ) 2, what percentage of elemental copper can you recover from the original solution? Materials: 1 M copper (II) nitrate 3 M hydrochloric acid 2 M sodium hydroxide 600 ml beaker 250 or 400 ml beaker Ice water Distilled water Stirring rod Bunsen burner Ring stand Al wire, 18 gauge or heavier Graduated cylinder ph paper Watch glass, 90 mm Goggles Acetone Procedures: Conversion 1: THIS IS ALREADY COMPLETED FOR YOU!!! Copper reacts with nitric acid to produce a brownish-orange gas called nitrogen dioxide. The blue color of the solution is characteristic of many copper compounds dissolved in water. You will be provided with 25 ml of 1 M solution of copper (II) nitrate. This solution contains 1.6 grams of copper. Since the brown nitrogen dioxide produced by the reaction is toxic, I have prepared this solution in advance for you. Conversion 2: CONVERTING COPPER (II) NITRATE TO COPPER (II) HYDROXIDE 1. Obtain 25 ml of copper (II) nitrate 2. Test the copper (II) nitrate solution with ph paper. DO NOT DIP THE PAPER INTO THE SOLUTION!!! Instead, take your clean stirring rod and dip into the solution. Carefully touch the ph paper with the tip of the stirring rod. Record the ph results in your data.

2 3. Obtain 25 ml of 2 M sodium hydroxide and also test it with ph paper using the same method as stated above. Remember that a ph less than 7 indicates an acid ph greater than 7 indicates a base ph equal to 7 indicates a neutral solution. Record your results. 4. Fill your 600 ml beaker one third full of ice water. Carefully place your beaker containing the copper (II) nitrate solution inside the 600 ml beaker so that the beaker floats in the water. 5. Slowly and cautiously add small portions of the sodium hydroxide solution to your copper (II) nitrate solution in the smaller beaker. Continuously mix the solution with a gentle swirling motion. Proceed until all 25 ml of the sodium hydroxide solution have been added. This neutralization process produces considerable heat, so stir well and add the sodium hydroxide solution SLOWLY! 6. Test the resulting solution with ph paper. If the test paper does not match the original color of the basic sodium hydroxide, add more sodium hydroxide to the 400 ml beaker while mixing until the color matches. The pale blue solid, termed a precipitate, is copper (II) hydroxide. The liquid which remains is sodium nitrate. Record your results. Conversion 3: CONVERTING COPPER (II) HYDROXIDE TO COPPER (II) OXIDE 1. Add 50 ml of distilled water to the beaker containing the copper (II) hydroxide precipitate. Heat to a gentle boil and stir until all the material is converted to a brown-black substance. This substance is copper (II) oxide. 2. Remove the stirring rod from the beaker. Let the beaker and the solution cool for 5 minutes. 3. Pour off the extra liquid (don t lose any solid!!) Wash the precipitate remaining in the beaker by adding 100 ml of distilled water and stirring gently. Let the precipitate settle for another 5 minutes and pour off the wash water, again leaving all solid particles in the beaker. This process is called decanting. Conversion 4: CONVERTING COPPER (II) OXIDE TO COPPER (II) CHLORIDE 1. Add 25 ml of 3 M hydrochloric acid to the black copper (II) oxide in the beaker. Stir gently or cover with a watch glass and swirl gently. The oxide will dissolve in a minute or two leaving a clear, aqua blue solution (the result of the formation of copper (II) chloride).

3 Conversion 5: CONVERTING COPPER (II) CHLORIDE BACK TO COPPER METAL 1. Add at least 1.5 grams of aluminum wire (~ 75 cm) to the copper (II) chloride solution. (Cut the wire and bend it in half; bend it again until it is a bit longer than a stirring rod. The bend it to form an L shape that will fit in the beaker so that a handle remains above the solution level.) 2. Immediately cover the beaker with a watch glass and allow it to stand. Watch what happens and record your observations. 3. As the aluminum wire grow copper hair, shake the wire gently to dislodge the copper. Cover and let the beaker stand overnight. Recovering Elemental Copper 1. Heat 200 ml of distilled water to a boil. 2. Remove any remaining aluminum wire from the beaker; with forceps remove any small bits of wire mixed in with the solid copper. 3. Decant and discard the clear liquid. 4. Wash the copper in the beaker twice with 50 ml portions of the hot distilled water stir and let settle decanting the wash water each time. Try not to lose any of the solid copper. 5. Weigh a clean watch glass to the nearest 0.01 g. Record the mass. Swirl the copper and remaining water in the beaker and quickly pour it onto the watch glass. 6. With a distilled water wash bottle, gently wash any remaining copper from the beaker into the watch glass. Allow the copper to settle and carefully pour off the excess water from the watch glass. CAUTION: Acetone is extremely flammable. For the next step of the experiment, be sure all burner flames are extinguished in the lab before proceeding! 7. Wash the copper on the watch glass with a small quantity of acetone (the amount will depend upon the size of the watch glass). 8. Pour off the acetone into a small beaker, being very careful not to lose acetone as before.

4 9. Wash the copper with a second portion of acetone and pour off the acetone as before. 10. After the second wash, allow the copper and watch glass to stand overnight in the fume hood until dry.

5 Recovery of Elemental Copper Report Sheet 1. Initial mass of copper (given) 2. Mass of copper and watch glass 3. Mass of watch glass 4. Mass of recovered copper 5. Percent yield (show calcs!) Mass of recoverd copper x 100 Initial mass of copper 6. Write and balance the formula equation for Conversion #1: copper + nitric acid copper (II) nitrate + nitrogen dioxide + water 7. Write and balance the formula equation for Conversion #2: copper (II) nitrate + sodium hydroxide copper (II) hydroxide + sodium nitrate 8. Describe the color of the ph paper when in contact with: a. copper (II) nitrate solution b. sodium hydroxide solution 9. Write and balance the formula equation for Conversion #3: Δ copper (II) hydroxide copper (II) oxide + water

6 10. Write and balance the formula equation for Conversion #4: copper (II) oxide + hydrochloric acid copper (II) chloride + water 11. Write and balance the formula equation for Conversion #5: copper (II) chloride + aluminum aluminum chloride + copper 12. Describe the color of your recovered copper. 13. In a perfect experiment, your percent yield would equal 100%. Hypothetically, what type(s) of error would result in a. a percent yield of less than 100% b. a percent yield of greater than 100%