Chapter 20 Laboratory: Quantitative Analysis 369fLTERING BARIUI m SULfATE
Barium sulfate can be obnoxious to filter. If your filter
paper is too fast (porous), some of the finely divided
barium sulfate passes through the filter paper. If your filter
paper is too slow, the barium sulfate may plug the filter
paper, causing the filtration to proceed at a snail’s pace (or
stop entirely).
After the liquid drains through the filter paper, examine the
filtrate in the receiving container. It should appear clear.
Any milkiness indicates that some of the solid barium
sulfate has passed through the filter paper. If that occurs,
the only real option is to repeat the procedure, using more
retentive filter paper. It’s pointless to evaporate the liquid
in the receiving container, because that liquid contains a
substantial mass of soluble salts in addition to the barium
sulfate that passed through the filter paper. Alternatively,
if the amount of barium sulfate that passed through the
filter paper appears to be small, you can simply note
the fact that some of the barium sulfate was lost during
filtration and use the value you obtain in the following
steps for the mass of barium sulfate obtained.8.fter all of the liquid has passed through the filter A
paper, rinse the filtrand two or three times with several
mL of distilled water to ensure that any soluble salts
are eliminated from the filtrand.- Remove the filter paper from the funnel and place it in
a drying oven or under a heat lamp to evaporate any
remaining liquid. After the filter paper and filtrand are
completely dry, reweigh the filter paper and product
and record the mass to 0.01 g on line R of Table 20-3.
Subtract the initial mass of the filter paper from the
combined mass of filter paper and filtrand to determine
the mass of barium sulfate, and record that value to
0.01 g on line S of Table 20-3.
The gram molecular mass of barium sulfate, BaSO 4 , is
233.43 g/mol, of which barium constitutes 137.33 g. Use
these values to calculate the mass of sulfate ions present
in the aliquot, and enter that value on line T of Table 20-3.
Calculate the mass of sulfate ions present per liter of
seawater, and enter this value on line U of Table 20-3.
dISpoSAL:
The waste solutions from this lab contain small amounts
of silver and barium, both of which are toxic heavy
metals. Any excess silver or barium ions present in
solutions can be precipitated with excess sulfate or
carbonate ions (for example, from a solution of sodium
sulfate or sodium carbonate) and filtered. dispose of the
solids as hazardous waste. Any remaining solutions can
be flushed down the drain with plenty of water.oALIpToN ACTIvITIES
If you have time and the required materials, consider
performing these optional activities:
- Repeat the experiment, using seawater collected from
a different location or at a different time of year. In
near shore waters, you can find the line where fresh
water meets the salt. At that point, especially on a
calm day and an incoming tide, there is likely to be
some degree of stratification, with the top water being
fresher than the bottom. - If you used actual seawater, repeat the experiment
using sea salt from the grocery store and compare
your results. - Repeat the experiment using “Instant Ocean” from the
pet store. - Repeat the experiment using water from a lake or pond.