Student s Name: Date: Background Preparation of copper(ii) sulfate from copper(ii) nitrate The purpose of this laboratory activity is to prepare copper(ii) sulfate from copper(ii) nitrate. This is done by using the following steps: 1. Precipitation of copper (II) hydroxide Cu(OH) 2 from copper (II) nitrate Cu(NO 3 ) 2 solution by the addition of NaOH solution. 2. Conversion of copper (II) hydroxide Cu(OH) 2 to copper(ii) oxide CuO by heating. 3. Neutralisation of copper (II) oxide CuO with sulfuric acid to form copper (II) sulfate CuSO 4. 4. Evaporation of copper (II) sulfate CuSO 4 (l) solution to form solid copper (II) sulfate CuSO 4 (s). Equipment and Chemicals analytical balance hot plate and magnetic stirrer beaker 250 ml (x 2) sodium hydroxide [NaOH] solution 2 mol L -1 (40 ml) R.O. water in wash bottle sulfuric acid [H 2 SO 4 ] 2 mol L -1 (30 ml) stirrer bar one boiling chip copper (II) nitrate trihydrate [Cu(NO 3 ) 2. 3H 2 O] (5g) spatula Safety dry filter paper on watch glass sodium hydroxide - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0360.htm sulfuric acid - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0362.htm copper (II) sulfate - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc14/icsc1416.htm H 2 SO 4 NaOH harmful CuSO 4.5H 2 O CuSO 4 copper2sulfate.doc Adapted from STAWA Exp 28 Page 1
Method Part A Precipitation of copper(ii) hydroxide Cu(OH) 2 from copper(ii) nitrate Cu(NO 3 ) 2 solution 1. Weigh out approximately 4.8 g of Cu(NO 3 ) 2. 3H 2 O into a TARED 250 ml beaker on the analytical balance. 2. Record the exact mass used: 3. Dissolve the copper (II) nitrate pentahydrate - Cu(NO 3 ) 2. 3H 2 O in about 20 ml of R.O. water. 4. Put the beaker on a magnetic stirrer and add a stirrer bar carefully to the solution. 5. Turn the stirrer on SLOW speed. 6. Slowly add 30 ml of 2 mol L -1 sodium hydroxide - NaOH solution. 7. Describe what you see happening in the beaker as you add the NaOH: Part B - Conversion of copper(ii) hydroxide Cu(OH) 2 to copper(ii) oxide CuO 1. Add 100 ml of R.O. water to the copper hydroxide - Cu(OH) 2 precipitate the beaker. 2. Keep the stirrer ON 3. Turn the heat on LOW and keep heating until the solution turns FROM LIGHT BLUE colour to BLACK. This is the colour of copper (II) oxide - CuO. 4. Turn OFF the hot plate and let the beaker cool down. 5. Without losing any of the SOLID, slowly DECANT as much of the liquid as possible from the beaker into another 250 ml beaker (labelled WASTE beaker). 6. To the first beaker (the one with the black solid in it), add about 100 ml of R.O. water. copper2sulfate.doc Adapted from STAWA Exp 28 Page 2
7. Use the magnetic stirrer to stir the SUSPENSION for one minute. 8. When the solid has settled to the bottom, DECANT the liquid into the WASTE beaker. Part C - Neutralisation of copper(ii) oxide CuO with sulfuric acid to form copper(ii) sulfate CuSO 4. 1. Put the beaker with the black solid suspension on the magnetic stirrer and set the stirrer to a SLOW stirring speed. 2. Slowly (and carefully) dropwise add about 20 ml of sulfuric acid - H 2 SO 4 to the suspension of CuO. 3. Look carefully to see if any of the black solid is still in the beaker. If there is, add more drops of sulfuric acid H 2 SO 4. 4. Use a magnetic rod to remove the stirrer bar. 5. Describe what you observed inside the beaker as the acid was added: Part D - Evaporation of copper(ii) sulfate CuSO 4 (l) solution to form solid copper(ii) sulfate CuSO 4 (s). 1. Add a boiling chip (anti-bumping granule) to the solution and heat the solution on the hot plate until the volume is reduced to about 10 ml. Use the markings on the side of the beaker as a guide to the volume. 2. Turn OFF the heat and take out the boiling chip. Use a clean spatula to do this. 3. Crystals of copper (II) sulfate should start to form as the solution cools down. If there is not enough time to precipitate out the crystals, put a label on the beaker with your name, date and compound s name/formula. Put the beaker in an approved storage cupboard until the next lesson. See the lecturer for a safe place to store the solution. copper2sulfate.doc Adapted from STAWA Exp 28 Page 3
Part E Weighing the copper(ii) sulfate crystals 1. Transfer the copper (II) sulfate pentahydrate crystals CuSO 4.5H 2 O to a pre-weighed or TARED filter paper or weighing bottle. Record the mass of crystals in the space: Post Lab Assignment 1. Write equations to represent the four steps in the preparation of CuSO 4.5H 2 O. Step 1 Step 2 Step 3 Step 4 copper2sulfate.doc Adapted from STAWA Exp 28 Page 4
2. Use the starting mass of Cu(NO 3 ) 2. 3H 2 O and the equations from Question 1. to calculate the theoretical amount of copper sulfate that you should have made. Show each step of your calculation in the space below: Step 1 Step 2 Step 3 Step 4 3. Calculate the percentage yield of copper(ii) sulfate pentahydrate based on the amount of copper(ii) sulfate pentahydrate that you made and the theoretical amount that you calculated in Question 2. mass of CuSO4.5H 2O produced % yield CuSO4.5H 2O = x mass of CuSO.5H O theoretical 4 2 100 copper2sulfate.doc Adapted from STAWA Exp 28 Page 5
5. a) Was your percentage yield for CuSO 4.5H 2 O = 100%? b) Briefly describe what events could have occurred during the preparation to give you a result other than 100% yield. 6. What could you do next time to improve your percentage yield of CuSO 4.5H 2 O? copper2sulfate.doc Adapted from STAWA Exp 28 Page 6