ELECTROCHEMISTRY cambridge as level Unit 6 lesson 1

This presentation is useful for CIE AS level studies.

1. ELECTROCHEMISTRY GRADE 9 (AS LEVEL CHEMISTRY)

2. OBJECTIVES:

3. Oxidation Number Rules The oxidation numbers (also known as oxidation state) is a number given to each atom or ion in a compound to keep track of how many electrons they have In a single ion or molecular ion, the oxidation number tells us how many electrons have been lost or gained Positive oxidation number = loss of electrons Negative oxidation number = gain of electrons Oxidation number rules The oxidation number (ox.no.) refers to a  single  atom in a compound

4. Redox Reactions Balancing Redox Reactions Oxidation numbers can be used to balance chemical equations Roman numerals between brackets are used to show the ox. no. of an atom that can have multiple oxidation states

5. steps: calculate oxidations numbers for all the elements in the equation. F igure out what is being oxidized and what is being reduced. W rite half reactions for the oxidation and reduction. B alance each half reaction: first, for the atoms other than O and H, then for O and H, and finally for charge by adding electrons. The oxidation and reduction half reactions are ready to be added back to together. Make sure that the number of electrons is the same in the oxidation and reduction half reactions. If they are not, multiply one or both of the half reactions to make the number of electrons the same. C ombine the oxidation and reduction half reaction, canceling out stuff that appears on both sides of the equation. To get rid of the H+ ions, add OH- (hydroxide) ions to both side. C ombine the H+ and OH- to make water, H2O. Finally, subtract out any H2O molecules you can from both sides of the equations. D o a final check to make sure that everything balances: both atoms and charge.

6. Oxidising & Reducing Agents potassium dichromate(VI) solution acidified with dilute sulphuric acid.

7. Oxidising agents are frequently used because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses. Group ions such as dichromate (Cr 2 O 7 2- ) and permanganate (MnO 4 - ) ions are strong oxidising agents in acidic solutions. They are useful in the chemistry lab when forming aldehydes, ketones and carboxylic acids from alcohol molecules. Hydrogen peroxide (H 2 O 2 ) is an example of a molecule which is a strong oxidising agent. It is used in everyday life as a means of breaking down coloured compounds, whether in clothes or hair.

8.  sodium tetrahydridoborate , NaBH 4

9. D

10. D

11. C

12. D

13. D

14. C

15. D

16. C

17. A

18. D