Chemicals from the Sea - Chemistry of NaCl

1. Syllabus/Unit: code: C2 Chemical ResourcesLesson number: 8Lesson Title: Chemicals from the sea - Chemistry of NaCl Connector: What factors can affect the healthy growth of a plant?

2. Extended Learning • Extended Learning task: • Due date: next lesson • Criteria for Grade C: • Criteria for Grade B: • Criteria for Grade A:

3. BIG picture Key Question: How are organisms classified? • How is this lesson relevant to every day life? Identify and maintain global diversity • What skills will you be developing this lesson? • HSW- by planning and carrying out an investigation/ Interpreting data/ evaluating an experiment • Numeracy- by using formulae in calculations • Literacy- by writing explanations using correctly spelt keywords and good grammar. • Team work- during a practical investigation • Self management- by completing an individual assignment by ….. • Participation- during a practical activity • Reflection- through self and peer assessment of each outcome Where does this lesson fit in to the rest of the topic? Lesson 5 • Quick Discussion: • What do you already know?

4. Keywords: • Brine • Solution mining • Subsidence • Bleach Put your hand up if there is any key word from the list that you don’t know the meaning of.

5. New Information for Learning Outcome 1 • The common name for salt is sodium chloride, NaCl. • Can be used to produce all sorts of material, not just flavour and preserve food. • But where do we get it from? • It can be made from salt water • It can also be obtained from salt deposits. • Underground in Cheshire and elsewhere in UK • Remains of ancient seas that have evaporated and been covered by rock • Machines cut through salt, forming caverns • Salt mined this way is used for cooking and salting roads during winter The chemical name for common table salt is sodium chloride: NaCl

6. Solution mining Salt is soluble in water. Concentrated salt solutions are called brine. Needed for industry, brine is mined using a method called solution mining: 3. This is a continuous process, needing little labour, keeping costs down 1. Water pumped from surface into deposit deep underground 4. Mining salt may cause subsidence - this is where land collapses downwards due to the mine, causing cracked buildings and holes in the ground. 2. NaCl dissolves in the water, brine is made, and the brine pumped to the surface

7. Create Evaluate Analyse Apply Understand Remember Demonstrate your Learning for Outcome 1 Apply (C) Suggest why salt for spreading on roads in the winter is mined using cutting machines, rather than by solution mining. Understand (D) What is brine and how and why is it made? Remember (E) State two uses of sodium chloride in food

8. Electrolysis of Concentrated Sodium Chloride Solution (Brine) H2 gas collected here Cl2 gas collected here At the cathode: 2H+ + 2e– → H2 At the anode: 2Cl– → Cl2 + 2e– Clearly describe and explain what will happen at each electrode when the switch is closed. Overall reaction:  2H+(aq) + 2Cl–(aq) → H2(g) + Cl2(g) A solution of NaOH is left in the cell.

9. Using ALL the key words, Describe in as much detail as possible the laboratory electrolysis of brine that you carried out. You should: • Explain electrolysis and describe the cell used. • Record what was observed during electrolysis. • Describe the chemical tests that were performed on the gaseous products. • Explain the chemical reactions at each electrode, using chemical equations. (What ions are present in the solution? To which electrode are they attracted? Why does one ion react in preference to the other?) • What substance is left behind in the cell? • Explain the terms oxidation and reduction and link them to the reactions at the electrodes. Key words: anode cathode electrolyte electrolysis ions electrons oxidation reduction OILRIG alkali

12. The industrial electrolysis of brine Two electrodes are needed to pass electricity into the brine Electrodes are made from inert materials like titanium to prevent reaction with brine or the products made Hydrogen forms at the negative electrode (the cathode) Chlorine forms at the positive electrode (the anode) NaOH stays dissolved in solution

13. Further questions about the electrolysis of brine What industry makes use of this process? Compare and contrast the laboratory electrolysis of brine with the industrial process. Explaining the reasons for the adaptations used in the industrial process. Why is this such an important industrial process? Why are inert electrodes used? What is the major disadvantage associated with the industrial process? Homework - due next lesson Produce an A4 poster showing the uses of the three products of this process.

15. New Information for Learning Outcome 2 • Brine electrolysis happens in a chlor-alkali plant. • The European chlor-alkali industry produces 10 millions tonnes of chlorine every year. • To do this, 36 billion kilowatt hours of electricity is used – enough to supply electricity to 7.5 million homes in the UK!

16. Sodium hydroxide + chlorine  sodium chloride + water + sodium chlorate New Information for Learning Outcome 2 The electrolysis of sodium chloride solution produces three very useful products: • Chlorine used for killing bacteria in water (sterilising it), for making chemicals like HCl, for bleach and making plastics like PVC. • Hydrogenused for making margarine and fertilizers, and for rocket fuel. • Sodium hydroxide used in many chemical reactions, such as making soap, neutralizing acids and making paper. It also reacts with chlorine to make bleach (sodium chlorate):

17. Keywords: Create Evaluate Analyse Apply Understand Remember Demonstrate your Learning for Outcome 2 Analyse (B) Produce a poster to describe and explain the process of brine electrolysis, giving the products formed, and explaining their applications. Apply (C) Produce a poster to describe the uses of chlorine, sodium hydroxide, and how both combine to make bleach Remember (E) Produce a poster to show the uses of hydrogen

18. Learning Outcome 2: Review Go back to your Learning Outcome grid and fill out the ‘How I did’ and the ‘Targets’ column.

19. oxygen removed reduction carbon monoxide +  + carbon lead lead oxide oxygen added oxidation redox = reduction andoxidation New Information for Learning Outcome 3 Oxidation: is the addition of oxygen to a substance and Reduction: is the removal of oxygen from a substance. Which substances are oxidized and reduced in this reaction? Reduction and oxidation always take place together. Why is this type of reaction called a redox reaction?

20. New Information for Learning Outcome 3 Oxidation also means loss of electrons in a reaction, and reduction is a gain of electrons....You can remember this using...............OILRIG!

21. Oxidation Is Loss of electrons Reduction Is Gain of electrons New Information for Learning Outcome 3 What does OILRIG stand for in terms of redox reactions?

23. heat New Information for Learning Outcome 3 In electrolysis, the substance that the current passes through and splits up is called the electrolyte. The electrolyte contains positive and negative ions. What happens to these ions during electrolysis? Negative ions move to the positive electrode and lose electrons. This is oxidation. Positive ions move to the negative electrode and gain electrons. This isreduction.

24. New Information for Learning Outcome 3 In the electrolysis of NaCl solution, the negative chloride ions (Cl-) are attracted to the positive electrode. Here, the Cl- ions lose electrons to make chlorine atoms, which then form chlorine molecules (Cl2). oxidized • Are the Cl- ions oxidized or reduced? • How many electrons are lost by each Cl- ion? • How many Cl- ions join to make a Cl2 molecule? • What is the half-equation for this redox process? one two 2Cl-  Cl2 + 2e-(oxidation)

25. For all ionic compounds containing a metal that is more reactive than hydrogen, electrolysis of a solution of the compound will produce hydrogen rather than the metal. New Information for Learning Outcome 3 In the electrolysis of sodium chloride solution, the Na+ions might be expected to form sodium at the negative electrode. Instead, hydrogen gas is produced here. This is because sodium chloride solution also contains H+ ions from some of the water: H2O (l)  H+ (aq) + OH- (aq). At the negative electrode, the H+ions compete with the Na+ions. The H+ions gain electrons; the Na+ ions stay in solution.

26. New Information for Learning Outcome 3 In the electrolysis of NaCl solution, the positive hydrogen ions (H+)are attracted to the negative electrode. Here, the H+ions gain electrons to make hydrogen atoms, which then form hydrogen molecules (H2). reduced • Are the H+ ions oxidized or reduced? • How many electrons are gained by each H+ ion? • How many H+ ions join to make a H2 molecule? • What is the half-equation for this redox process? one two 2H+ + 2e- H2(reduction)

27. 2NaCl (aq) + 2H2O (l)  H2 (g) + Cl2 (g) + 2NaOH (aq) New Information for Learning Outcome 3 Sodium chloride solution has four types of ions: • Na+ and Cl- ions from the sodium chloride • H+ and OH- ions from the water. The Cl- ions form chlorine at the positive electrode and the H+ ions form hydrogen at the negative electrode. So, what’s left? Na+ and OH- ions are left behind and so a solution of sodium hydroxide (NaOH) is formed. What is the overall equation for the electrolysis of a sodium chloride solution?

28. New Information for Learning Outcome 3

29. Create Evaluate Analyse Apply Understand Remember Demonstrate your Learning for Outcome 3 (A*) In terms of electrons, using suitable equations, what happens during the electrolysis of brine? (B) Give the names of the two gases produced in electrolysis of brine. Give the tests that could be used to identify them.

30. Learning Outcome 3: Review Go back to your Learning Outcome grid and fill out the ‘How I did’ and the ‘Targets’ column.

31. Review for Remembering • Stand up if you have met all three lesson outcomes? • If not what do you need to do next in order to meet the outcome? Record this in your diary as part of your homework. • Is there any part of the lesson you think you need to go over again next lesson? • Tell the person next to you three things you have learnt this lesson. • How will you remember this for your exam?

32. Science Department Lesson plan Teacher information Poster paper Glue Colour pens Colour pencils Scissors Rulers Laptops if available Reference books if available