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Skip to 0 minutes and 10 seconds So now we’re going to produce copper sulfate on a much smaller scale, which reduces the risk for students. We’re going to use, surprisingly, more concentrated sulfuric acid. We’re going to use 1.4 molar solution. But that will help us produce a near saturated solution of copper sulfate at room temperature. The 1.4 molar solution is just below the level where it would be marked as corrosive. We’re going to use 15 centimetres cubed of the acid. And you might have a technician or somebody else pre-measure out the solution for students so it can go into a boiling tube. Instead of heating the acid on the Bunsen burner, we’re going to use a kettle of water that’s just off the boil.

Skip to 0 minutes and 54 seconds And we’re going to stand our acid in there for about two minutes to warm it up before we add our copper oxide. So now our acid has heated for at least two minutes. We’re going to add our copper oxide, which we’ve pre-weighed out between 1.8 and 2 grammes. Again, having this pre-weighed can save time in the classroom. We’re going to add about half of the copper oxide now. And gently shake the tube to mix the copper oxide with the sulfuric acid. Once the reaction has started to subside and there’s no more fizzing, we can add the rest of the copper oxide and shake a bit more. Ideally, we want to get most of that copper oxide to mix together.

Skip to 1 minute and 41 seconds We then leave that in the hot water for another two minutes. After waiting at least two minutes in the hot water, and the longer the better, we’ve now got a solution of our copper sulfate with some excess copper oxide at the bottom. We can now filter that while it’s still hot through our filter funnel, much as we did before. Trying to get as much of that copper oxide at the bottom into the filter funnel, as it makes disposal easier.

Skip to 2 minutes and 15 seconds Now we’ve finished filtering, the residual copper oxide that’s left in the filter paper can go into the bin.

Skip to 2 minutes and 22 seconds What we’re going to do now is heat up the conical flask and we’re going to add a couple of anti-bumping granules in there just to be on the safe side. This allows a nucleation point to occur so we have some smooth boiling. If you don’t have anti-bumping granules, and only add a few of them, add a couple of bits of broken porcelain crucible and that will do the same job. We’re now going to heat this up and boil it for no more than two minutes once it reaches boiling point.

Skip to 2 minutes and 59 seconds OK, now our solution has been boiling for almost two minutes. We’re going to in a moment turn the Bunsen burner off. And then we’re going to let it cool for 30 seconds before pouring it into a plastic Petri dish.

Skip to 3 minutes and 18 seconds It’s very important at this stage not to let it dry out inside the flask and start spitting. If you hear any popping noises then it’s time to remove it from the heat. Make sure that students use tongs to hold the conical flask and not bits of paper towel because there’s a good chance they will slip. And then they can pour this solution, which is now quite concentrated, into the Petri dish.

Skip to 3 minutes and 44 seconds If we leave that cool for around five minutes we should start seeing crystals form. If you don’t start seeing crystals after that time, then break the end of a wooden splint or matchstick and put that into the solution which will create a nucleation point to start growing the crystals.

Learning with smaller practicals

This reaction is a much smaller scale version of making copper sulfate crystals, which can usually be completed within a lesson.

Using much smaller quantities generates far less waste and the practical itself reduces hazards and risks associated with hazards to a much more acceptable level.

The sulfuric acid we are using is more concentrated than before. It is 1.4moldm-3, but this helps us get a near-saturated solution of copper sulfate. This is also the highest concentration that we can use before the acid would need to be marked as “corrosive” and this would require additional considerations, such as indirect vented goggles, rather than ordinary safety spectacles.

We are also using only a very small excess of copper oxide. This could be pre-measured for each student group, to save time in the lesson, if those measurement skills are not the key learning objective for this activity.

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Teaching Practical Science: Chemistry

National STEM Learning Centre