Illustrated Guide to Home Chemistry Experiments

276 DIY Science: Illustrated Guide to Home Chemistry Experiments

When material at one temperature comes into

contact with material at another temperature,

heat flows from the warmer material to the

cooler material until thermal equilibrium is

attained when both materials are at the same

temperature. In a controlled environment, such

as our calorimeter, no heat is gained from or

lost to the environment, so the heat gained

by the (originally) cooler material equals the

heat lost by the hotter material. (In practice, of

course, there are minor heat gains or losses,

even with the calorimeter, but these gains or

losses are quite minor relative to the large

changes that we’ll measure in this laboratory.)

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ balance and weighing boat

£ calorimeter

£ thermometer

£ graduated cylinder, 100 mL

£ test tube (2)

£ test tube holder

£ beaker, 600 mL

£ hotplate

£ lead and iron shot (see Substitutions and modifications)

£ water

In this laboratory, we’ll determine the specific heat of two metals,
lead and iron, by heating a known mass of each metal to a known
temperature, and then adding the hot metal to a known mass of
cooler water at a known temperature and allowing the system
to come to thermal equilibrium. Heat flows from the hot metal,
warming the cooler water. Because the amount of heat lost by
the metal is equal to the amount of heat gained by the water, we
can calculate the specific heat of the metal by measuring the
temperature increase of the water.

When the unit quantity is specified in mass, the heat transfer
equation is:

q = mcΔT

where Q is the amount of heat transferred, m is the mass of the
sample, c is the specific heat of the substance, and ΔT is the
change in temperature. Because the heat transfer for the metal
and the water is equal—although with different signs, because
heat is lost by the metal and gained by the water—we can express
this equivalence as:

qwater = –qmetal
or
(mcΔT)water = –(mcΔT)metal

The specific heat of water is known to be 4.181 Joules per gram
per Kelvin (J/(g · K) or J · g–1 · K–1). Because the masses and
temperatures of the metals and water will be measured and are
therefore known, the only unknown is the value for the specific

LABORATORY 15 .3:

dETERmINE THE SpECIfIC HEAT of A mETAL

SBSTITUTIU oNS ANd modIfICATIoNS

• You may substitute a small Petri dish or similar
  container for the weighing boat.


• You may substitute a sauce pan or similar container
  for the 600 mL beaker.


• You may substitute any appropriate heat source for
  the hotplate.


• You may substitute other forms of lead and iron, as
  long as the samples fits inside the test tube. Lead shot
  may be obtained from laboratory supply houses or
  from sporting goods stores that sell shotgun reloading
  supplies. (Lead shot used in shotgun shells is an alloy,
  but contains a high percentage of lead; some shotgun
  shells use copper-plated steel shot instead of lead
  shot.) At the expense of some accuracy, you may
  substitute wheel weights or fishing sinkers for the lead
  shot. Because these items are often made from a lead
  alloy rather than pure lead, your experimental results
  may differ significantly from the values obtained with a
  pure lead sample. You may substitute small steel nuts
  or bolts for the iron shot. Sporting goods stores sell
  lead airgun pellets, which are almost pure lead, and
  BBs, which are copper-plated steel shot.