PREPARATION OF SILVER CHROMATE
Introduction
Silver chromate (Ag2CrO4) is an insoluble, bright-red, ionic compound which precipates when an aqueous solution
of silver nitrate (AgNO3) reacts with an aqueous solution of potassium (VI) chromate (K2CrO4).
2 AgNO3(aq) + K2CrO4(aq)  Ag2CrO4 (s) + 2 KNO3(aq)
In this experiment you will be given a mixture of silver nitrate and potassium chromate of unknown proportions
and will have to use ideas about limiting reactants to work them out.
Materials and Equipment
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Vial containing silver nitrate/potassium chromate
mixture – treat as TOXIC!
Distilled water
100 ml beaker
Heating apparatus
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Filtration apparatus
Analytical balance
Watch glass
Silver nitrate solution (0.2 M)
Potassium chromate solution (0.1 M)
Method*
OBSERVATIONS SHOULD BE RECORDED DURING EACH STEP
ALL WASTE SHOULD BE TREATED AS TOXIC AND DISPOSED OF ACCORDINGLY
1. Accurately weigh your vial, empty the contents into the 100 ml beaker and re-weigh.
2. Add 100 cm3 distilled water to the beaker
3. Cover the beaker with a clean watch glass and heat until almost boiling, then turn down the heat and maintain
at hot but not boiling (approx 90OC) for 10 minutes.
4. Leave beaker to cool for 30-60 minutes, time allowing.
5. Whilst waiting: write your name in pencil on a filter paper, flute it, then place it in a funnel and place the funnel
in a 50 ml conical flask ready for filtration.
6. Filter your cool solution, scraping any crystals off the side of the beaker with a spatula, and use a small amount
of distilled water to wash any remaining residue into the filter/funnel.
7. Wash the precipitate in the funnel with a small amount of distilled water, ensure that no yellow crystals
remain.
8. Place 2-3 cm3 of filtrate into each of two test tubes. Add 10 drops of silver nitrate solution to one and of
potassium chromate solution to the other. Look for and record the presence or absence of a red-precipitate.
This will tell you which reactant was present to excess.
9. Carefully remove your filter paper then place it on a watch glass and leave to dry in the drying oven overnight
10. Remove the filter paper from the drying oven and accurately weight it.
*There is lots of waiting around here so use the time to plan out your calculations so you can just plug the numbers
in later. You could also do some general stoichiometry problems whilst you wait.
Calculations
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You need to use your experimental data to determine the mass of each reactant in your initial mixture.
Challenge yourself to work out the calculations without help….although I will give you pointers if you really
need them.
Source: http://www.lahc.edu/classes/chemistry/arias/Exp%204%20-%20Limiting%20RF11.pdf