Cells and Batteries Section 1.4

Cells and BatteriesCells and BatteriesSection 1.4

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Review-Section 1.3Review-Section 1.3What 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.

The PlanThe PlanDiscuss 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.

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:1. Dry cells2. Wet cells

BatteriesBatteries

Batteries are two or more cells connected together.

A battery is essentially a can full of chemicals that produces electrons.

Battery TerminalsBattery Terminals Every battery has two terminals:

1) One terminal is marked (+) or positive.2) 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.

Dry CellsDry CellsDry 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.

Devices that are Devices that are Powered by Dry CellsPowered by Dry Cells

Dry CellsDry CellsThe type of cell we use every day.

Dry cells are commonly used in portable devices (e.g., flashlights).

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How Do Dry Cells Work?How Do Dry Cells Work?1. Chemical reaction

releases free electrons. 2. Electrons travel from the

negative terminal of the cell.

3. Electrons travel through the electricity-using device.

4. Electrons travel back to the positive terminal of the cell.

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Structure of Dry CellsStructure of Dry CellsAn electrolyte is 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.

Most Common Type of Dry Most Common Type of Dry CellCell

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:

1.Cost2.Electricity output3.Shelf life4.Reliability5.Leak resistance

History of the BatteryHistory of the BatteryThe 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.

Wet CellsWet CellsA 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.

How Do Wet Cells Work?How Do Wet Cells Work?1. Acidic electrolyte eats away at the zinc

(-) electrode = producing electrons.2. Reaction of the electrolyte and copper

(+) electrode does not eat away the copper = leaves it positive.

3. Electrons travel along the electrodes (-) to (+).

4. Electrons travel out the (-) zinc terminal.

5. Electrons travel through the wire.6. Electrons travel back to the (+) copper

terminal.

Dry Cells vs Wet CellsDry Cells vs Wet Cells

Primary vs Rechargeable Primary vs Rechargeable CellsCells

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.

Rechargeable CellsRechargeable CellsRechargeable cells are used to start

cars, portable phones and computers.

Only certain electrodes and electrolytes can be used. Nickel oxide and cadmium is one combination of chemicals often used in secondary cells.

Cells can never be fully recharged; they eventually wear out and die.

Car BatteryHow does a car battery work?

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ElectrochemistryElectrochemistryElectrochemistry is the study of

chemical reactions using electricity.

It can involve:1.Electrolysis2.Electroplating3.Anodizing,4.Electrorefining.

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ElectrolysisElectrolysis 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.

ElectroplatingElectroplating 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.

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How Does Electroplating How Does Electroplating Work?Work?

1. Needs a liquid electrolyte.

2. Negative electrode is the metal that will form the coating.

3. Positive electrode is the object to be plated.

4. 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

Other Electrochemical Other Electrochemical ApplicationsApplications

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).

How Does Electrorefining How Does Electrorefining Work?Work?

1. Need a strong acid electrolyte.2. Negative electrode is the impure

bar with gold.3. Positive electrode is a pure thin

strip of gold. 4. 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.

HomeworkHomeworkCheck and Reflect #2, 4, 5, 6 and

7 (p. 294).