The product we all instantly recognise and know as salt is sodium chloride. Sodium
chloride is the source of sodium, a key nutrient in our diet. Throughout history,
humans have been using salt to preserve meat, clean wounds and make soap.
In chemistry, the term salt refers to a group of ionic compounds
formed by the neutralisation of an acid by a base. Sodium chloride is just one example
of a salt. Today I'm going to be preparing a different soluble salt: copper sulfate.
The name of the salt has two parts: the first part of the name comes from the metal,
metal oxide or metal carbonate; the last part of the name
comes from the acid. This is a very rewarding practical - especially if you get well-formed
crystals at the end - this would explain why this is such a popular experiment.
On first appearance, preparing a soluble crystal in the lab is a straightforward practical. After
all, all you need to do is follow a method. However, every year a high number of incidents
and accidents are reported. Here I'm going to show you how to prepare some copper sulfate crystals.
I'm going to point out where things could potentially go wrong
and where we're going to be using a safer method than the standard one seen in the textbooks.
But don't worry, we're going to follow all the same steps, just in a safer way.
First things first, eye protection on! I'm now going to measure out 15 centimetres-cubed
of sulfuric acid using a measuring cylinder and pour it into a boiling tube.
Next, I'm going to half fill this beaker with hot water for my ready-boiled kettle.
Now, I will gently stand the boiling tube in the hot water for about two to three minutes.
While I wait, I will prepare the base. I need to measure out between 1.8 and 2 g of
black copper oxide powder using a measuring boat. Now add half of the copper oxide to the acid...
agitate gently...
then place the boiling tube back in the water. This method of heating the
sulfuric acid is safer than heating it on a bunsen burner, because it minimises the risk,
of both knocking over hot sulfuric acid when adding the copper oxide,
and the very hot sulfuric acid spilling over the beaker when the copper oxide is added, due to a
rapid reaction taking place. When the reaction subsides add the rest of the copper oxide.
You'll notice that some of the black copper oxide powder remains. Let's take a moment to
think about what has happened here. Remember a salt has formed by the neutralisation of an acid
by a base. Copper oxide has reacted with sulfuric acid to form copper sulfate and water. This is a
neutralisation reaction because the negative sulfate ions have reacted with the positive
copper ions to form copper sulfate and water. We added an excess of copper oxide to ensure
that the reaction has completed and that all of the acid has been neutralised.
In this next step, we're going to separate the product (copper sulfate)
from the unreacted reactant (copper oxide) using filtration. We will be using fluted
filter paper. To do this we will start by folding some filter paper in half...
opening it up and folding it in half again...
opening it up, half again...
and once more in half again.
We will then start making indents between these segments.
Here is one I made earlier!
I have already placed a filter funnel in a 100 centimetre-cubed conical flask
and I will place my fluted filter paper into my funnel.
Now I'm going to pour my copper sulfate into the filter paper.
Be careful when pouring that none of the copper sulfate solution goes over the edge.
The copper sulfate solution is now dripping through the filter paper, down the filter
funnel into the conical flask. And inside the filter paper we can see some black copper oxide.
The copper oxide is insoluble so cannot go through the filter paper: this is called the residue.
Now we need to remove excess water by evaporation to make a concentrated solution of copper sulfate.
Before we start, I need to add two to three anti-bumping granules.
These will help maintain a smooth boiling action
but do not react with any of the particles in the flask.
Now, I'm going to place my conical flask on my tripod
and turn the bunsen burner to the blue roaring flame.
It's important that you let this gently simmer for two minutes only. If you hear any spitting
or popping noises you must turn the heat off immediately and never let the solution boil dry.
I'm going to use a heatproof glove to pour the hot solution into the evaporating dish or petri dish.
Pour it carefully.
If the crystals don't form quickly we can use a wooden spill
and place it inside the evaporating basin. This will speed up the reaction
as it creates a rough surface for the crystals to form on.
As you can see, we have produced some amazing copper sulfate crystals.
If you leave them to cool slowly overnight you could even end up with crystals
that look like this. It might be tempting to take them home
but it's important that you don't because they do carry three hazard warning symbols.
Now that you know how to make copper sulfate crystals, starting with an insoluble oxide,
why not use the same sequence of steps to make other soluble salts? You will need to
start by working out which reactants to use and don't forget to use the student safety
sheets to make a risk assessment before you start. Why not use the additional resources
attached to this video to design a plan to make copper chloride or zinc sulfate crystals?
Thank you for watching, have fun with your experiments!
Inspiring your teaching and learning.