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I am learning to understand redox reactions EXAM TIPS: You will be expected to write half equations for the reactions at the electrodes.You will be expected.

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Presentation on theme: "I am learning to understand redox reactions EXAM TIPS: You will be expected to write half equations for the reactions at the electrodes.You will be expected."— Presentation transcript:

1 I am learning to understand redox reactions EXAM TIPS: You will be expected to write half equations for the reactions at the electrodes.You will be expected to write half equations for the reactions at the electrodes. In half equations, the number of electrons MUST balance the number of charges on the ion.In half equations, the number of electrons MUST balance the number of charges on the ion.

2 I am learning to understand redox reactions Outcomes: I will demonstrate I understand at Grade C by Recall the transfer of electrons at the anode and cathode. Recognise oxidation and reduction at electrodes. Predict the products of electrolysis. Outcomes: I will demonstrate I understand at Grade A by Explain the transfer of electrons in electrolysis. Construct half equations Explain how water affects the products of electrolysis. Objectives: I will understand That electrons are transferred during electrolysis. That electrolysis can be represented in half equations. That water affects electrolysis.

3 I am learning to understand redox reactions heat Positive ions move to the negative electrode (cathode) and gain electrons (Red) Negative ions move to the positive electrode (the anode) and lose electrons (Ox)

4 I am learning to understand redox reactions What is Oxidation?

5 I am learning to understand redox reactions Oxidation Oxidation is the gain of oxygenOxidation is the gain of oxygen Rust is an example of oxidationRust is an example of oxidation What is reduction?

6 I am learning to understand redox reactions Reduction Reduction is the loss of oxygen Metal Displacement reactions are an example of reduction. Metal Displacement reactions are an example of reduction. lead oxide + carbonlead carbon monoxide + oxygen removed reduction oxygen added oxidation

7 I am learning to understand redox reactions

8 Reduction and oxidation always take place together. Why is this type of reaction called a redox reaction? Why is this type of reaction called a redox reaction? redox = reduction and oxidation Oxidation IsIs Loss of electrons Reduction IsIs Gain of electrons OILRIG YOU SHOULD ALWAYS WRITE THIS NEXT TO THE QUESTION

9 I am learning to understand redox reactions magnesium + oxygen magnesium oxide 2Mg (s) O 2 (g) 2MgO (s) + Magnesium burns in oxygen to form Magnesium oxide. The Magnesium obviously is oxidised but what happens to the oxygen?

10 I am learning to understand redox reactions Redox Reactions can also be explained in the terms of losing or gaining electrons Mg Mg 2+ O 2- O + oxidized (electrons lost) reduced (electrons gained) Mg is oxidised (lost electrons) O is reduced (gained electrons)

11 I am learning to understand redox reactions In terms of oxygen In terms of electrons OxidationLoss of electrons ReductionLoss of oxygen Copy and Complete the table...

12 I am learning to understand redox reactions Half Equations Redox reactions involve the transfer of electrons.Redox reactions involve the transfer of electrons. Equations written to show what happens to the electrons during oxidation and reduction are called half-equations.Equations written to show what happens to the electrons during oxidation and reduction are called half-equations. oxidation: Mg Mg e - magnesium + oxygen magnesium oxide 2Mg (s) O 2 (g) 2MgO (s) + reduction: O 2 + 4e - 2O 2-

13 I am learning to understand redox reactions 1.Na + + e - _____ 2. Pb 2+ + ____ e - Pb 3.Cu 2+ + _____e - ____ 4. ___H + + _____e - H 2 Oxidation or Reduction? Na 2 2Cu 2 2 REDUCTION

14 I am learning to understand redox reactions 2K + + ____e - 2K 2Cl - - ___e - Cl 2 2 REDUCTION 2 OXIDATION Oxidation or Reduction?

15 I am learning to understand redox reactions

16 What redox processes occur at the electrodes during the electrolysis of molten lead bromide (PbBr 2 )? What is the overall equation for the electrolysis of molten lead bromide with state symbols? At the negative electrode: Pb e - Pb (reduction) lead bromide lead + bromine PbBr 2 (l) Pb (l) + Br 2 (g) At the positive electrode: 2Br - Br 2 + 2e - (oxidation) Electrolysis of molten PbBr 2 – redox equations

17 I am learning to understand redox reactions We need an Anode (to take electrons) Cathode (to give out electrons) Pb and Br ions.

18 I am learning to understand redox reactions Your Turn – Complete these equations with states 2FeCl 3 (aq) Anode(+)? Cathode(-)? 2Fe(s) + 3Cl 2 (g) 2Cl - (aq) Cl 2 (g) + 2e- Fe 3+ (aq) + 3e- Fe (s) OXIDATION REDUCTION

19 I am learning to understand redox reactions How does water effect the products of electrolysis? Water contains hydrogen and hydroxide ions. When solutions of ions in water are electrolysed, hydrogen may be produced at the positive electrode. This happens if the other positive ions are metals more reactive than hydrogen.

20 I am learning to understand redox reactions Summary notes When positively charged ions reach the negative electrode they gain electrons to become neutral atoms. Gaining electrons is called reduction, so the positive ions have been reduced. Ions with a single positive charge gain one electron and those with a 2+ charge gain 2 electrons. At the positive electrode, negative ions lose electrons to become neutral atoms. This is oxidation. Some non-metal atoms combine to form molecules, for example bromine forms Br 2. We can represent the changes at the electrodes by half equations. For lead bromide. At the negative electrode: Pb 2+ +2e - Pb At the positive electrode:2Br - Br 2 +2e - Water contains hydrogen and hydroxide ions. When solutions of ions in water are electrolysed, hydrogen may be produced at the positive electrode. This happens if the other positive ions are of metals more reactive than hydrogen. Oxidation is loss (OIL) reduction is gain (RIG). In half equations the number of electrons must balance the number of charges on the ion.

21 I am learning to understand redox reactions Check your understanding 1.What happens in electrolysis to copper ions, Cu 2+, at the negative electrode? 2.What happens in electrolysis to chloride ions, Cl -, at the positive electrode? 3.Why are ions of metals always reduced in electrolysis? ANSWERS: 1.They are discharged, gain electrons and are reduced to form copper atoms. 2.They are discharged, lose electrons and are oxidised to form chlorine atoms which then bond to form chlorine molecules (diatomic molecules) 3.All metals form positive ions so they are attracted to the negative electrode where they gain electrons. CLICK AGAIN FOR THE ANSWERS

22 I am learning to understand redox reactions Extra Notes

23 I am learning to understand redox reactions

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