Program Support Notes

Transcription

1 Video Education Australasia Bringing Learning to Life Program Support Notes Middle - Senior Secondary Acids and Bases 30mins Teacher Notes by Keir Strahan, B.Sc. Dip.Ed. Produced by Video Education Australasia Commissioning Editor Christine Henderson B.Sc. Ph.D. Dip.Ed. Executive Producer Mark McAuliffe Dip.Art (Film & TV) Dip.Ed. B.Ed. Ph.D. Video Education Australasia Pty. Ltd. Suitable for: Chemistry To order or inquire please contact VEA: Australia 111A, Mitchell Street, Bendigo, Victoria 3550 FREECALL: Phone: (03) Facsimile: (03) New Zealand PO BOX 4390, Shortland St., Auckland FREECALL: Facsimile: vea@vea.com.au Website WARNING The Copyright proprietor has licensed the motion picture contained on this video cassette for non-theatrical use only and prohibits any other use, copying, reproduction or performance in public, in whole or part. The penalties for unauthorised copying of this program include a $50,000 fine for individuals and a $250,000 fine for institutions. These notes can be freely copied for classroom use only.

2 For Teachers: Brief Summary of Program Acids and bases are all around us. The program features the following: early theories of Arrenhius and Lowry-Bronsted. Valence structures, exposed protons and proton transfer. Diprotic and triprotic acids linked to structures. Amphiprotic example given by hydrogen sulphate ion. The ph scale and the use of indicators to measure ph. Conjugate pairs and strengths of acids with strong acids giving weak conjugate bases. Standard reactions: acid + metal, acid + oxide, acid + carbonate, acid + hydrogen carbonate. Introduction Acids and bases are an important part of life. From their presence in food, to their use as cleaning agents and electrolytes, this program introduces them in familiar settings. The corrosive properties of acids and bases are demonstrated by the impact that acid rain has on the environment and building structures, and by the caustic properties of alkaline oven cleaners. The chemistry of acids and bases is then examined. The theories of Svante Arrenhius and Lowry- Bronsted lead into an analysis of the structures of a number of common acids. The need for an exposed proton is clearly explained and the mechanism of an acid-base reaction is graphically demonstrated as we see a proton transfer between water and hydrochloric acid. Examples of diprotic and triprotic acids are provided and the amphiprotic nature of the hydrogen sulphate ion is addressed with clear graphics. The ph scale and its relationship to the concentration of dissolved hydronium ions is linked with the use of indicators in analytical chemistry. Indicators are described as weak acids and a number of common indicators are used to show changes in ph. Acid-base conjugate pairs are then considered and the extent that an acid ionises is used to explain the differences observed in the strengths of certain acids. The program concludes with a look at some common acid-base reactions as acids are mixed with metals, oxides, carbonates and hydrogen carbonates. Chemical equations accompany all of the reactions that are demonstrated. Program Timeline Introduction Properties and uses Summary What are acids and bases Summary The ph scale Summary Indicators Summary Acids and bases conjugate pairs and strengths Summary Common reactions of acids Summary Conclusion Credits Acids and bases end 2

3 For Students: While Viewing the Program 1. Acids and bases are 2 chemical groups. What other types of chemical groups can you name? 2. What does corrosive mean? 3. What common 2 pollutants produced from the burning of fossil fuels lead to acid rain? 4. What effect does acid rain have on trees, buildings and statues? 5. What does the word neutralise mean to you? 6. What does it mean when we say that acids and bases neutralise each other? 7. Heartburn is a burning sensation in your chest that is caused by hydrochloric acid from the stomach affecting the oesophagus. Which property of acids and bases is responsible for this burning? 8. Why is vinegar useful as a cleaning product? 9. Explain why indicators are useful in analytical chemistry that involves acids and bases. 3

4 10. What is an electrolyte? Why do acids make good electrolytes when they are dissolved in water? 11. How did Svante Arrenhius explain the fact that acids and bases neutralise each other? 12. What do all acids have in common? 13. How many electrons and protons do hydrogen atoms have? 14. What is the Lowry-Bronsted theory of acids and bases? 15. When sulphuric acid is dissolved in water it ionises. Is this an acid-base reaction? Explain your answer. 16. Annotate the equation for the reaction between hydronium ions and hydroxide ions in order to show that it is an acid-base reaction. 17. Ethanoic acid has the molecular formula CH 3 COOH. It contains 4 hydrogen atoms and yet it is monoprotic. Explain why ethanoic acid is monoprotic. 18. What is an amphiprotic substance? Write out the formulas of some amphiprotic substances. 4

5 19. What is ph? 20. What is the ph of solutions with H 3 O + concentrations of 10-2, and ? Which of these ph values are acidic and which are basic? Demonstrate that 10-3 is a larger number than 10-8 and hence show that acidic solutions have a higher concentration of ions than basic solutions. 21. How can you measure the ph of substances? 22. Name 4 common substances and their ph values. Which are acidic and which are basic? 23. What are indicators? 24. How does Universal Indicator differ from other indicators? Why can it be used to measure ph whereas an indicator such as Phenolphthalein cannot? 25. What is a conjugate base? Why is the chloride ion (Cl - ) the conjugate base of hydrochloric acid (HCl)? 26. What is the difference in molecular formula between a conjugate acid and its base? Use an example in your answer. 5

6 27. Explain how measuring the conductivity of an acid in solution can identify it as being a strong or weak acid. 28. Is the chloride ion (Cl - ) a strong or weak conjugate base? 29. Vinegar contains ethanoic acid (CH 3 COOH) which is a weak acid. Is its conjugate base relatively weak or strong? 30. Compose a generalisation for the strengths of conjugates acids and bases compared to the strengths of the acids and bases from which they are derived. 31. Why is the reaction between magnesium (Mg) and hydrochloric acid (HCl) not classed as an acid base reaction? 32. Write a general equation for the reaction between an acid and an oxide. 33. Write a general equation for the reaction between an acid and a carbonate. 34. Write a general equation for the reaction between an acid and a hydrogen carbonate. 6

7 Web Site References Clearly covers the theory of acids and bases Directory with many links to acid-base sites Introduction to acids and bases with examples of common acid-base reactions Introductory unit into acids and bases Directory with many sites that relate to acids and bases and how they impact on the environment A fun game of memory that asks players to match definitions to other terms Other Relevant Programs Available from VEA Chemical Equations Our Chemical Environment Series The Super-Charged World of Chemistry Series Applied Chemistry Science Bank Series The Amazing Mole Please visit our website for many more relevant programs VEA Bringing Learning to Life 7