UNIT 3:

1. UNIT 3: Acids, Bases and Metals

2. Acids and Alkalis Can you think of some common, household acids and alkalis? • USES: • WASP STING IS ALKALINE IT IS NEUTRALISED BY VINEGAR AN ACID • LIME AN ALAKLI IS ADDED TO ACIDIC SOIL • VINEGAR IS USED AS A PRESERVATIVE • AMMONIA IS USED AS A HOUSEHOLD CLEANER Acids Alkalis Vinegar Fruit Juice Baking Soda Indigestion Powder Oven Cleaner In Toothpaste

3. Laboratory Acids and Alkalis HCl(aq) NaOH(aq) H2SO4(aq) KOH(aq) NH4OH(aq) CH3COOH(aq) HNO3(aq) LiOH(aq) You MUST remember the FORMULAS of these!!! Can you work out the FORMULAS from the name?

4. Testing for Acids and Alkalis SUBSTANCES THAT CHANGE COLOUR WITH CHANGING pH INDICATORS Used to measure acidity or alkalinity of SOLUTIONS pH scale Scale runs from under 0 to above 14 Anything under 7 is acidic Anything above 7 is alkaline Neutral 7 only

5. The pH Scale The pH scale is based on the pH of pure water being =7 When we measure the pH of a solution, we are measuring to what degree a solute has changed the pH of water Universal indicator to cover the whole range Strong acidweak acidneutralweak alkalistrong alkali Red pink orange green blue/green blue purple

6. Rules when testing pH 1. Prepare a test solution 2. Add universal indicator (or drop onto pH paper) 3. Allow colour to develop 4. Compare with standard colour chart

7. Testing for pH Name of Solution pH Acid / Alkali / Acid Follow the rules for “Testing pH” and test 5 different solutions

8. Non-metal Oxides RED Colourless, pungent gas RED Colourless, odourless gas Colourless or brown Pungent gas RED GREEN Colourless and odourless

9. Non-metal Oxides Oxides of carbon and sulphur are prepared by burning sulphur and carbon in air. Oxides of nitrogen are prepared by sparking air RULE: Oxides of NON-METALS make ACIDIC SOLUTIONS EXCEPTION: Oxide of HYDROGEN is NEUTRAL (water)

10. Starter question • Which of the following substances when dissolved in water would produce an acidic solution • Magnesium oxide • Hydrogen oxide • Ammonium hydroxide • Phosphorus oxide Answer 4) Explanation the rule is soluble non-metal oxides make acidic solutions

11. Metal Oxides Experiment 1: 1. Add a tiny quantity of CALCIUM OXIDE into a dimple tray 2. Add a few drops of WATER 3. Test the pH of the solution with UNIVERSAL INDICATOR Appearance of Oxide Name of Oxide pH of solution

12. Metal Oxides When a metal oxide reacts with water, the METAL HYDROXIDE is formed eg Sodium oxide reacts and forms SODIUM HYDROXIDE Na2O (s) + H2O (l) 2NaOH (aq)

13. Making Metal Oxides Experiment 2: 1. Ignite a little of MAGNESIUM RIBBON 2. Allow magnesium to burn and form MAGNESIUM OXIDE 3. Drop the white ash onto a dimple tray 4. Check the pH of the SOLUTION Write the balanced equation for making MAGNESIUM OXIDE:

14. Metal Oxides RULE: Oxides of METALS make ALKALINESOLUTIONS HOWEVER: Like non-metal oxides, they must be SOLUBLE in water for them to change the pH of water

15. THURSDAY 8th OCTOBER • Today’s plan: • Looking at INSOLUBLEMETAL OXIDES • AMMONIA GAS and its pH

16. Insoluble Oxides and Hydroxides Experiment: 1. Add a small quantity of copper (II) oxide to a test-tube 2. Add approx 5ml of water 3. Shake the tube and try and dissolve the solid 4. Use a dropper to transfer a sample of the clear liquid to the spotting tile 5. Check the pH with Universal Indicator Some metal oxides (such as copper (II) oxide) are INSOLUBLE in water, as these don’t dissolve, they CANNOT alter the pH of water.

17. Ammonia NH3(g) is ammonia gas (covalently bonded compound) When dissolved in water ammonium hydroxide is formed The equation for the reaction when ammonia gas dissolves in water to form ammonium hydroxide NH3(g) + H2O  NH4OH(aq) THIS SOLUBLE HYDROXIDE MUST BE AN ALKALI Fountain Experiment

18. Summary Flow-chart

19. Starter Question Put these four oxides in order of the one which will give the HIGHEST pH to the one that will give the LOWEST pH: Hydrogen oxide Magnesium oxide Carbon dioxide Copper (II) oxide (The flow-chart from last day will help you!!)

20. Acids HCl (aq) H2SO4(aq) HNO3(aq) CH3COOH (aq) Which element is COMMON to all acids?

21. Acids Looking at the formula of the acids – which type of BONDING would you expect? Think…….. Would you expect it to CONDUCT ELECTRICITY?? Experiment: 1. Set up the circuit shown 2. Use HYDROCHLORIC ACID and determine if it conducts 3. Repeat with both SULPHURIC and NITRIC ACIDS

22. Acids Acids are: Compounds which dissolve in water to give a pH less than 7 All acids contain the element HYDROGEN Acid solutions are able to conduct electricity

23. Electrolysis of Acids Experiment: • Set up apparatus as shown – using DIRECT CURRENT (DC) • Upturn a test-tube FULL OF WATER over each electrode • Turn on the power supply – set to 6V • Collect a tube-full of gas from one electrode. • Keep the tube inverted to prevent losing any gas. • Test the tube for HYDROGEN GAS. • Repeat for other electrode.

24. Electrolysis of Acids Draw a labelled diagram of the apparatus used last day Underneath your diagram copy the note below: Electrolysis is the breaking down of a compound using electricity. When acids undergo electrolysis, HYDROGEN GAS is formed at the negative electrode.

25. Why does hydrogen form? Although acids are made up of non-metals they exist as IONS. The hydrogen ions (H+) pick up electrons from the negative electrode and produce hydrogen gas. H+ H+ H+ H e- H H+ H+ e- H H+ e- e- +ve -ve

26. Ions in Acids

27. Alkalis Think!! What common alkalis have you come across before?? How many can you name??

28. Alkalis Can you now put these into a table? Can you get their formula? Can you work out the IONS present?

29. The pH scale - dilution • Experiment: • Measure 10ml of acid into test-tube (A) – test pH • Take 1ml of Aand dilute with 9ml of water (B) – test pH • Take 1ml of B and dilute with 9ml of water (C) – test pH • Repeat for test-tubes D, E and F – testing pH of each Results: Test-tube pH

30. The pH scale - dilution Answer these questions in your NOTES jotter. Write in sentences – these will be your notes for this activity!! • What happens to the ACIDITY as the ACID is diluted? • What is happening to the concentration of H (aq) ions? • What happens to the pH as the ACID is diluted? +

31. The pH scale - dilution • Experiment (This is a repeat of yesterday’s using ALKALI): • Measure 10ml of ALKALI into test-tube (A) – test pH • Take 1ml of A and dilute with 9ml of water (B) – test pH • Take 1ml of B and dilute with 9ml of water (C) – test pH • Repeat for test-tubes D, E and F – testing pH of each Results: Test-tube pH

32. The pH scale - dilution Answer these questions in your NOTES jotter. Write in sentences – these will be your notes for this activity!! • What happens to the ALKALINITY as the ALKALI is diluted? • What happens to the concentration of OH (aq) ions? • What happens to the pH as the ALKALI is diluted? -

33. H+(aq) and OH-(aq)Ions + NEUTRAL solutions contain an EQUAL concentration of H(aq) and OH(aq) ions. ACIDIC solutions contain a GREATER concentration of H(aq) than OH(aq) ions. ALKALINE solutions contain a GREATER concentration of OH(aq) than H(aq) ions. - + - - +

34. Water The chemical name for water is HYDROGEN OXIDE The expected bonding is From this bonding COVALENT BONDING WATER SHOULDN’T CONDUCT ELECTRICITY Water DOES conduct electricity For water to conduct, there MUST be charged particles The charged particles present are IONS