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Find supporting resources including pause-and-think questions, technician notes, worksheets, integrated instructions, and more at: https://rsc.li/2NtkWSD • Discover videos for more core practicals for 14–16 at: https://rsc.li/36XHfXi • Learn how to prepare a sample of pure, dry, hydrated copper sulfate crystals from copper oxide. This practical experiment develops skills in measuring chemical substances, filtration, evaporation and crystallisation to produce hydrated copper(II) sulfate crystals. • Chapter titles • 00:00 Opening title • 00:10 Introduction • 01:30 Base + acid reaction • 03:36 Filtration • 05:13 Evaporation • 06:27 Crystalisation • Transcript • 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 neutralization 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 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 grams 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 minimizes the risk, both of 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 neutralization of an acid by a base. Copper oxide has reacted with sulfuric acid to form copper sulfate and water. This is a neutralization 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 neutralized. • 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. • [continues]
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