Electrolysis of aqueous solutions - PowerPoint Presentation

1. Electrolysis of aqueous solutionsMonday, 05 October 2020CHAPTER 5: CHEMICAL CHANGESDo Now: These are the answers… what could the questions be?ElectrolysisAnodeCationElectrolyteElectrodeSpec 5.4.3.4

2. PROGRESS INDICATORSGood progressOutstanding progressGrade 1-3Electrolyse a solution. Predict observations and products of electrolysis.Identify unknown products in the gas state. Outline a method for electrolysis.Grade 4-6Write a detailed plan, including a hypothesis, explaining how to use electrolysis to collect and test gases. Recognise the risks associated with electrolysis. Accurately show that hydrogen or chlorine is made. Grade 7-9Recognise and give justifications for how risks can be minimised in an electrolysis experiment, taking into account the hazards of the reactants and the products. Justify modifications in the method to improve accuracy. Write half equations to show what happens at the anode and cathode during electrolysis.Monday, 05 October 2020

3. PracticalMonday, 05 October 2020AIMInvestigate what happens when aqueous solutions are electrolysed using inert electrodesSAFETYCopper(II) chloride solution– IRRITANTOxygen gas – OXIDISINGHydrogen gas – EXREMELY FLAMMABLEChlorine gas – TOXICThe electrolysis of brine produces a solution of sodium hydroxide, which is corrosive.Wear chemical splash proof eye protection and if you are collecting a gas by displacement, wear nitrile gloves and only complete the practical in a well-ventilated room. Take extra care if you are asthmaticEQUIPMENT100 cm3 measuring cylinder2 × carbon electrodes2 × crocodile clips2 × wires1 × low voltage lab packBunsen burner and safety equipment1 mol/dm3 copper(II) chloride solution3 × ignition tubes with bungslitmus papersplintseye protection and nitrile gloves

4. Method1. Pour approximately 50cm3 copper (II) chloride solution into the beaker. 2. Add the petri dish lid and insert the carbon rods through the holes. The rods must not touch each other. 3. Attach crocodile leads to the rods. Connect the rods to the dc (red and black) terminals of a low voltage power supply4. Select 4 V on the power supply and switch on. 5. Look at both electrodes and record your initial observations in the table below. 6. Use forceps to hold a piece of blue litmus paper in the solution next to the anode (positive electrode) and identify the element? Write all your observations in a table like this one. 7. Rinse the electrochemical cell apparatus and collect a new set of electrodes. Repeat steps 1‒8 using the other solution sodium chloride and complete the following tasks to show your understanding of the chemistry of electrolysis. a. Draw a fully labelled diagram of your electrochemical cell.

5. ObservationsMonday, 05 October 2020

6. Demonstrate Answer the following questions1) Explain why aluminium cannot be extracted from its oxide by reduction with carbon. (1 mark)2) Label the diagram of electrolysis equipment (5 marks)3) Describe the electrolysis in terms of the ions moving (2 marks)4) Explain why cryolite is added (1 mark)5) Give two reasons why the electrolysis of aluminium is expensive (2 marks) 6) Give 3 uses of aluminium and explain why it is used for each purpose (3 marks)7) Write an equation to summarise the overall process (2 marks) 8) HT ONLY Write the half equations at the anode and the cathode and determine whether each reaction is oxidation or reduction (4 marks)

7. Demonstrate – Mark Scheme 1) Aluminium cannot be extracted from its oxide by reduction with carbon because aluminium is more reactive than carbon 2) On next slide3) The positive ions are attracted to the negative electrode (cathode) The negative ions are attracted to the positive electrode (anode)4) Lowers the melting point so less energy is needed5) The oxygen reacts with the carbon anode to produce carbon dioxide so the carbon anode gradually burns away.Large amounts of energy are used in the extraction process 6) Air craft = Strong / Low densityDrinks Cans = Easy to shape / Corrosion resistantSaucepans/cookers/ Boilers = Good conductor of heatOverhead electricity cables = Good conductor of electricityMirrors = Highly reflective 7) 2Al2O3  4Al + 3O28) Cathode Al3+ + 3e−  Al REDUCTIONAnode 2O2−  O2 + 4e− OXIDATIONSAIn red pens please

8. Demonstrate – Mark Scheme 2)SAIn red pens please

9. Connect MarkColourTask0-6PinkDefine electrolysisDraw a diagram of electrolysis equipmentSuggest why cryolite is addedSuggest one reason why electrolysis is expensive7-14Yellow1. Suggest one reason why electrolysis is expensive2. Write the balanced equation for the electrolysis of aluminium3. Describe why the anode must be constantly replaced.15-20GreenWrite the half equation for what is happening at the cathodeWrite the half equation for what is happening at the anodeState which reaction is reduction and which is oxidationComplete your connect task in green pens

10. PLENARYMonday, 05 October 2020Match the name of the test to the description.Test for hydrogenTest for oxygenTest for carbon dioxideTest for chlorinea burning splint held at the open end of a test tube of the gas makes a pop sounda glowing splint inserted into a test tube of the gas relightsshake or bubble the gas through limewater, the limewater turns milky (cloudy)the gas bleaches a damp litmus paper and turns it white