Cells and Batteries

1. Cells and Batteries Section 1.4 http://mustridenow.com/build-lightweight-lithium-battery/

2. Review-Section 1.3 • What is more dangerous, current or voltage? Why? Both are dangerous. • Current- When someone is shocked it’s the amount of current that causes the damage. Even small current can kill. • High voltage- Dangerous because it drives current.

3. The Plan • Discuss types of cells, watch video clips and an animation, look at batteries, and brainstorm. • I can explain the difference between dry and wet cells. • I can explain how a battery is made.

4. Electrochemical Cell • The energy source of a pacemaker is usually an electrochemical cell. • An electrochemical cell is a package of chemicals designed to produce small amounts of electricity; produces electricity from chemical reactions. • Two main types of cells: • Drycells • Wet cells

5. Batteries • Batteries are two or more cells connected together. • A battery is essentially a can full of chemicals that produces electrons.

6. Battery Terminals • Every battery has two terminals: • One terminal is marked (+) or positive. • Other terminal is marked (-) or negative. • In an AA, C, or D cell (normal flashlight batteries), the ends of the battery are the terminals. • In a large car battery, there are two heavy lead posts that act as the terminals.

7. Dry Cells • Dry cells are the electricity-producing cells that has its electrolyte in the form of a paste, usually in a sealed case. • Called “dry” because the chemicals are in a paste so they can be placed in any position without leaks.

8. Devices that are Powered by Dry Cells

9. Dry Cells • The type of cell we use every day. Dry cells are commonly used in portable devices (e.g., flashlights). https://musicianstools.wordpress.com/2009/01/07/stay-gripped-to-your-music-with-the-ibikeconsole/ http://vlab.ethz.ch/flashlight/

10. How Do Dry Cells Work? • Chemical reaction releases free electrons. • Electrons travel from the negative terminal of the cell. • Electrons travel through the electricity-using device. • Electrons travel back to the positive terminal of the cell. http://pixshark.com/dry-cell-battery-diagram.htm

11. Structure of Dry Cells • An electrolyteis a paste or liquid that conducts electricity, for it contains ions. • The electrolyte reacts with two metals called electrodes. As a result of this reaction, one electrode becomes positive, the other negative. • The electrodes are connected to the cell’s terminals. In the dry cell, electrons leave from the negative electrode, and return to the positive electrode.

12. Most Common Type of Dry Cell • Many types of metals and electrolytes can be used (e.g., zinc, manganese (IV) oxide, zinc chloride, and lithium). • An alkaline cell is the most common type of dry cell because it offers a good combination of: • Cost • Electricity output • Shelf life • Reliability • Leak resistance

13. History of the Battery • The 1st battery was created by Alessandro Volta in 1800. • To create this battery he used alternating layers of zinc, blotting paper soaked in salt water, and silver. This arrangement was known as the voltaic pile.

14. Wet Cells • A wet cell is “wet” because it uses a liquid electrolyte, which is usually an acid (sulfuric acid). • Common in motorized vehicles. • Wet cells are generally cheaper and easier to make than dry cells, but they are not as safe for they are highly corrosive and may leak.

15. How Do Wet Cells Work? • Acidic electrolyte eats away at the zinc (-) electrode = producing electrons. • Reaction of the electrolyte and copper (+) electrode does not eat away the copper = leaves it positive. • Electrons travel along the electrodes (-) to (+). • Electrons travel out the (-) zinc terminal. • Electrons travel through the wire. • Electrons travel back to the (+) copper terminal.

16. Dry Cells vs Wet Cells

17. Primary vs Rechargeable Cells • The dry cells and wet cells are called primary cells. • A primary cell is a cell that produces electricity by means of a chemical reaction that cannot be reversed. • A rechargeable cell (or a secondary cell) is a cell that produces electricity by means of a chemical reaction that can be reversed by using an external source to run electricity back through the cell.

18. Rechargeable Cells • Rechargeable cells are used to start cars, portable phones and computers. • Only certain electrodes and electrolytes can be used. Nickeloxide and cadmium is one combination of chemicals often used in secondary cells. • Cells can never be fully recharged; they eventually wear out and die.

19. Car Battery • How does a car battery work? http://cheapcarbatteryhouston.com/blog/

20. Electrochemistry • Electrochemistry is the study of chemical reactions using electricity. • It can involve: • Electrolysis • Electroplating • Anodizing, • Electrorefining. http://drfus.com/electrochemistry-lab-experience

21. Electrolysis • Electrolysis is the breaking down of a substance by an electric current. • It was used to discover new elements and split water, and eventually led to a new field of science: electrochemistry. • Many industrial processes use electrolysis to separate useful elements from solutions.

22. Electroplating • Electroplating is the use of electricity to coat a thin layer or metal on to an object. • This process can produce cheaper, stronger, and less corrosive products. https://chemistry58.wikispaces.com/Electroplating

23. How Does Electroplating Work? • Needs a liquid electrolyte. • Negative electrode is the metal that will form the coating. • Positive electrode is the object to be plated. • Flow of electrons through the electrolyte deposits atoms from the positively charged metal on to the negatively charged object. http://www.explainthatstuff.com/electroplating.html

24. Other Electrochemical Applications • Anodizing is a process to coat aluminum parts with a layer of aluminum oxide. This makes the aluminum much stronger (e.g., iPods). • Electrorefining is used to remove impurities from metals (e.g., AuNO3).

25. How Does Electrorefining Work? • Need a strong acid electrolyte. • Negative electrode is the impure bar with gold. • Positive electrode is a pure thin strip of gold. • Flow of electrons causes the gold from the impure bar to dissolve and then attach to the strip of pure gold. It can produce very pure gold.

26. Homework • Check and Reflect #2, 4, 5, 6 and 7 (p. 294).