Illustrated Guide to Home Chemistry Experiments

298 DIY Science: Illustrated Guide to Home Chemistry Experiments

SBSTITUTIU oNS ANd modIfICATIoNS

• If you don’t have patch cables, you can make your own
  by using paper clips as field-expedient alligator clips.
  Wrap each end of a copper wire tightly around a paper
  clip and crimp it into place with pliers. (If possible,
  solder the wire to the paper clips.).


• You may substitute another color for the red LED, but
  different colors of LEDs require different voltages to
  illuminate. Red LEDs typically require at least 1.8V
  to 2.1V, which is less than the approximately 2.7V
  delivered by the magnesium/copper cell used in this
  session. Orange LEDs typically require 2.2V to 2.3V
  and yellow LEDs 2.4V to 2.5V, and so will probably
  illuminate when connected to a magnesium/copper
  cell. Green LEDs typically require 2.6V or more, and so
  may not illuminate with a magnesium/copper cell. Blue
  and white LEDs typically require 3V or more, and so will
  not illuminate when connected to a magnesium/copper
  cell. (If you insist on a different color, you can always
  build two cells and link them in series.)


• If you do not have a bench solution of 2 M hydrochloric
  acid, you can make it up by transferring about 33 mL
  of concentrated hydrochloric acid or about 39 mL of
  31.45% hardware-store muriatic acid to about 100 mL
  of water in the beaker and then making it up to about
  200 mL. The exact concentration is not critical.

The law of conservation of energy says that

energy can neither be created nor destroyed,

but can be transformed from one form to

another. For example, an electric generator

converts mechanical energy into electric energy,

a motor converts electric energy into mechanical

energy, and an incandescent light bulb converts

electric energy into light energy and heat energy.

Chemical energy is another form of energy

and—as is true of all forms of energy—can be

converted to other forms of energy.

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ digital multimeter (dmm)

£ patch cables with alligator clips (2)

£ LEd, red (1)

£ beaker, 250 mL (1)

£ steel wool or sandpaper

£ pieces of magnesium, iron, and copper (one each) to

use as electrodes. If they are long and skinny, and

flat, that’s best.

£ hydrochloric acid, 2 m (~200 mL)

In this lab session, we’ll transform chemical energy into electric
energy and use that electric energy to do work; specifically, to
light an LED. Electric energy has two key metrics, which can best
be understood by analogy with plumbing. Just as a differential in
water pressure forces water to flow through a pipe, a differential
in electrical pressure—called voltage, denominated in volts,
and abbreviated V—forces electricity to flow through a wire or
other conductor. And, just as the amount of water transferred
can be specified as a flow rate—denominated in gallons/minute,
liters/second, or some other unit of measure—the flow rate of
electricity is called current, and denominated in amperes or
amps (abbreviated A), where one ampere represents a current
flow of one coulomb per second. In this lab session, we’ll measure
voltage and current in a voltaic cell.

LABORATORY 1 6.4:

oBSERvE ENERGy TRANSfoRmATIoN (voLTAGE ANd CURRENT)

CUTIOA nS

Hydrochloric acid is corrosive and emits strong

irritating fumes. Wear splash goggles, gloves, and

protective clothing.

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