Hi everyone,
This video will show you the actual experimental steps and data collected for the Gravimetric
Analysis for an Unknown Sulfate lab. You may be asked questions related to the procedure
or data shown in the video. When the video focuses on specific measurements of mass,
please record those values in your Gravimetric Analysis Lab Report.
The first thing we need to do is to measure out 0.3 to 0.4 g of the unknown sulfate which
comes in a small vial. To do that we first tare the balance to make sure it starts from
zero. Then we place a 250-mL beaker and record its mass. After that we add some unknown sulfate
salt using a scoopula.
This is the mass of the beaker with the unknown sulfate salt which you should record on your
lab report.
To dissolve the unknown sulfate solid, we add 50 mL water, measured using a 100-mL graduated
cylinder, followed 20 drops of 6M hydrochloric acid. We gently pour the water into the beaker
and use a dropper to add the 6M HCl. We then mix the solution components together.
The next thing we do is set up a ring stand and wire gauze with a Bunsen burner so we
can heat the mixture until just before it boils. This will help to form larger crystals
for the barium sulfate product.
While this solution is being heated, we measure 25 mL of 0.1 M barium chloride using a 100-ml
graduated cylinder. Once we turn off the Bunsen burner, we slowly add the barium chloride
into the hot solution. This was done by pouring the solution from the graduated cylinder through
the stirring rod into the beaker.
As you notice a cloudy mixture forms in the beaker. The cloudiness is a sign that a precipitate
or solid has formed in the solution. We let the precipitate settle to the bottom for 20
minutes.
While that’s going on, now we heat the crucible to remove any contaminants that may add to
the mass of the crucible. After two minutes of heating and letting the crucible cool down,
we weigh the mass of the empty crucible. You should record this number in your lab report.
Once the 20 minutes have passed, we now need to filter the mixture containing the precipitate
to obtain just the solid. First we must fold an ashless filter paper to form a cone that
we can put into our funnel. To help the paper stick to the funnel, we moisten the paper
with water.
Next we mix the precipitate and solution together and slowly pour it down the funnel lined with
the filter paper. At the end of the filtration process, all the white precipitate is stuck
on the wet filter paper.
We take the wet filter paper and fold it into a small piece and place it in the crucible.
Next we are ready to recover the product. This is done by heating the crucible to high
heat such that filter paper decomposes. This heating is done inside the fume hood. At the
start, we use lower heat on the Bunsen burner to dry the filter paper.
As the heating continues the filter paper begins to char as you can see. Eventually
the entire paper turns black. At this point, we turn up the Bunsen burner to higher heat
and continue to heat the crucible until all the paper decomposes to carbon dioxide.
At the end, you see only the white precipitate of the barium sulfate. We let the crucible
cool down, weigh it and then reheat it again at high heat. The purpose here is to make
sure that all the paper is completely decomposed.
We then weigh the crucible again. If the difference is less than 0.005 g, then we can stop. The
final mass of the crucible with the product is shown here.