Batteries Chapter 2, Section 3 p54-57

The First Battery Energy can be transformed from one form to another – Batteries transform chemical energy into electrical energy – Chemical energy: energy stored in chemical compounds

Luigi Galvani Accident led to research and development of battery – Galvani studying anatomy of frog Brass hook holding leg muscle in place Touched hook to iron railing, leg muscle twitched – Hypothesis: “animal electricity” present only in living tissue » Later proven incorrect

Alessandro Volta Volta believed Galvani’s observations was the result of a chemical reaction – Chemical reaction: a process in which substances change into new substances with different properties

Alessandro Volta Hypothesis: – Chemical reaction occurred between two different metals (iron and brass) and salty fluids in leg Test: – Piece of paper soaked in salt water between zinc and silver – Produced current when wire was connected to zinc and copper Additional Test: – Added more layers » Zinc, paper, silver, zinc, paper, silver, etc – More current produced

Alessandro Volta Volta built the first electric battery by layering zinc, paper soaked in salt water, and silver – Made discovery public in 1800 – Basis of more powerful batteries today

Electrochemical Cells Electrochemical cell: device that transforms chemical energy into electrical energy – Volta’s battery electrochemical cells Each pair of zinc and silver layers with soaked paper – Electrodes: two different metals in an electrochemical cells immersed in an electrolyte Volta: silver & zinc – Electrolyte: substance that conducts electric current Volta: salt water

A Simple Cell Chemical reactions occur between electrolyte and electrodes in electrochemical cell. – Figure 14 Electrolyte: dilute sulfuric acid – Dilute: mixed with water Electrodes: copper & zinc Terminal: part of an electrode above surface of electrolyte – Used to connect cell to a circuit

A Simple Cell These reactions cause one electrode to become negatively charged and the other to become positively charged – Voltage between electrodes (opposite charges) Causes charges to flow – Connect terminals and charges flow from one terminal to the other Produces current in wire – Charges flow back through electrolyte to make complete circuit

Batteries Battery: combination of two or more electrochemical cells in a series – “Batteries” in flashlight technically cells “Connected in series” – Positive terminal connected to negative terminal – Total voltage = sum of individual cells

Wet Cells Wet cell: electrochemical cell in which electrolyte is a liquid – Volta’s battery (salt water) – Car batteries Electrolyte: sulfuric acid Electrodes: lead metal & lead oxide

Dry Cells Dry cell: an electrochemical cell in which electrolyte is a paste – Flashlight batteries Electrodes: carbon & zinc

Homework Read Chapter 2, Section 3, p54-57 Answer ?s 1-2, p57

Wet Cell Battery 2 pieces aluminum foil (10 cm x 30 cm) – Roll up & crumble one end put in beaker cm double thick square piece paper towel – Set on top of aluminum foil in beaker 3 copper wires (80 cm uninsulated) – 1: wrap one end around top of aluminum foil in Jar A, attach other end to bulb holder – 2: attach one end to bulb holder, curl rest of wire into ball and place on top of paper towel in jar B – 3: wind one end around top of aluminum foil in Jar B. Curl rest of wire into a ball and plac eon top of paper towel in Jar A – Don’t let wire & aluminum foil touch in jars

Wet Cell Battery Pour bleach (electrolyte) into each jar until wire completely covered Bulb glow & continue for several hours until chemical reaction stops Add tsp baking soda at top of each jar temporary increases conductivity of bleach – More current flows through circuit – Bulb glows more brightly for short time