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B-4
f.
Equation for the formation of H
2(g)
from H2SO
4(aq)
and zinc metal.
REAGENTS AND EQUIPMENT
acetone
ethyl alcohol
6.0 M ammonia (NH3 )
2.5 M sodium hydroxide (NaOH)
6.0 M sulfuric acid (H2SO
4
)
Hirsch funnel and filter paper
zinc metal
EXPERIMENTAL PROCEDURE
In this Experiment you will carry out some reactions starting with the copper(II) sulfate that you prepared
last week in Experiment A.
Part I. Preparation of Copper(II) sulfate Solution
Put on your safety glasses. Obtain your copper(II) sulfate crystals from your laboratory instructor.
They will have been marked as part of Experiment A. Add 10 mL of deionized water to the beaker
containing your copper(II) sulfate and gently stir to dissolve the solid. If some of the solid remains
undissolved, place the beaker on a hot plate, and heat gently to redissolve the remaining crystals.
Part II. Reaction Scheme A: Tetraamminecopper(II) sulfate monohydrate ([Cu(NH3)
4
]SO
4
H2O
(s)
)
In the presence of low concentrations of NH3*, an insoluble copper compound is formed. To form the
initial precipitate in the reaction sequence, use a Pasteur pipette to transfer 8 - 10 drops of CuSO
4
from
Part I to a large watch glass. Add 3 drops of 6.0 M NH3 to the watch glass, one drop at a time, with
gentle swirling of the solution to mix the reagents. Observe the formation of a precipitate. If no
precipitate is formed, continue adding NH3
one drop at a time, with swirling, until a permanent
precipitate forms. Describe this precipitate on your Observations Sheet.
Now add 10 drops of 6.0 M NH3 to the mixture on the watch glass. This creates a relatively high
concentration of NH3 in solution
.
What happens to the precipitate? Record your observations. Now add
2-3 mL of ethyl alcohol from a squeeze bottle to the solution on the watch glass, swirl, and record your
observations. The solid compound formed in alcohol is tetraamminecopper(II) sulfate monohydrate.
Dispose of the precipitate into the toxic waste container in the fumehood.
*
An aqueous NH3 solution is weakly basic due to the following equilibrium:
