Illustrated Guide to Home Chemistry Experiments

104 DIY Science: Illustrated Guide to Home Chemistry Experiments

dISoALp S : The filtrate from step 19 contains only sodium sulfate

and a small amount of copper. you can flush it down the sink with

plenty of water. The used filter paper can be disposed of with

household waste.

Item Data

A. Crude copper sulfate _________.___ g

B. Filter paper _________.___ g

C. Filter paper plus purified copper sulfate _________.___ g

D. Purified copper sulfate (C – B) _________.___ g

TABLE 6-3: Recrystallization of copper sulfate—observed and calculated data

RQEWEvI UESTIOnS

q 1 : The solubility of copper sulfate pentahydrate is 2033g/L at 100°C, which means that 305 g should dissolve in 150 mL of
water at 100°C. Why do you suppose we used only 250 g of crude copper sulfate rather than 305 g?

q: 2 We obtained about an 80% yield (roughly 200 g of purified copper sulfate from 250 g of crude copper sulfate). We might have
improved the percent yield somewhat by dissolving more than 250 g of crude copper sulfate initially, but at best that method would still
result in about a sixth of the crude copper sulfate going to waste. What method might we use to obtain much higher percent yields?

q: 3 A chemist requires copper sulfate of at least 99.9% purity for a particular procedure. She recrystallizes crude copper sulfate as
we have done, but analysis shows that her purified copper sulfate is only 99.4% pure. What might she do to obtain copper sulfate of
99.9% or higher purity?

dRAR .m y CHERvENAk CommENTS:

Paul has also started purchasing sodium

bicarbonate from the grocery store, because

it’s much, much cheaper and just as pure (if

not purer, as it’s routinely used in baking) than

the containers that he buys from his usual

laboratory chemical suppliers!