Illustrated Guide to Home Chemistry Experiments

Chapter 9 Laboratory: Introduction to Chemical Reactions and Stoichiometry 171

LABORATORY 9 .3:

oBSERvE A SINGLE dISpLACEmENT REACTIoN

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ balance and weighing paper

£ test tube (2)

£ test tube rack

£ graduated cylinder, 10 mL

£ sandpaper or emery board

£ toothpicks or wood splints

£ thread or string (~15 cm)

£ aluminum granules, turnings, or shot (~1 g)

£ iron or steel nail

£ hydrochloric acid, concentrated (~5 mL)

£ copper sulfate pentahydrate (~2.5 g)

£ water

SBSTITUTIU oNS ANd modIfICATIoNS

• You may substitute any type of scrap aluminum (such
  as aluminum foil or aluminum beverage cans) for the
  aluminum granules or shot, although the reaction
  rate may be lower. If you substitute scrap aluminum,
  use sandpaper or a similar abrasive to remove ink,
  paint, plastic coating, the oxidation layer, and other
  contaminants from its surface. Alternatively, you can
  produce aluminum filings by using a file on a piece of
  scrap aluminum stock.


• You may substitute any form of metallic iron or steel
  for the nail, including iron filings or steel wool (be
  sure to wash steel wool to remove soap and other
  contaminants).


• You may substitute muriatic acid from the hardware
  store for the hydrochloric acid. If you use muriatic
  acid, make sure the concentration is 30% or higher.

In a single displacement reaction, a more active

element displaces a less active element in a

compound, forming a new compound that

incorporates the more active element and

releasing the less active element in elemental

form. The reaction of an active metal with an

acid is a common type of single displacement

reaction in which the metal is oxidized to a

cationic oxidation state and the hydrogen

present in the acid is reduced to elemental

hydrogen. The fizzing and bubbling that occurs

when an active metal comes into contact with

a strong acid is caused by the emission of

gaseous hydrogen.

A nonchemist might believe that the metal “dissolves” in the acid.
That’s not true, of course. When we dissolve table salt or sugar in
water, for example, no chemical reaction occurs. We can recover
the solute unchanged, simply by evaporating the solvent. But
when we “dissolve” a metal in an acid, evaporating the liquid does
not allow us to recover the metal unchanged. Instead, the metal
has been converted to a salt by a single displacement reaction.

Different metals have different reactivity, as shown in Table 9-3.
The most active metals, such as lithium and potassium, react
(sometimes explosively) even with cold water to release hydrogen
gas. Less active metals, such as magnesium and aluminum, do
not react with cold water, but do react with steam, particularly
if the metal is finely divided and the steam is superheated. Still
less active metals, such as cobalt and nickel, do not react with
water in any form, but do react with acids to release hydrogen
gas. Finally, the least active metals, from antimony and bismuth
to platinum and gold, do not react even with acids under normal
circumstances. (Even platinum and gold do react with aqua regia,
a mixture of concentrated hydrochloric and nitric acids.)

Another common type of single displacement reaction is the
reaction of a solid metal immersed in a solution of a salt of
another metal. For example, an iron (or steel) nail immersed
in a solution of copper sulfate becomes plated, because the
copper ions are reduced to metallic copper while the iron metal
is oxidized to iron ions. If sufficient metallic iron is available,
eventually all of the copper ions are reduced, leaving metallic
copper in a solution of iron sulfate.