Identifying unknown substances (including barium)

Hello, my name is Mrs. Collins, and I'm going to be taking you through the learning today. This lesson forms part of the unit Chemical Analysis and is called Identifying Unknown Substances. So let's get on with the lesson. During today's lesson, you will learn how to conduct ion identification tests using flow charts and accurately record observations to ensure correct and safe lab practises. Here are the key words for today's lesson. Precipitate, ion, cation, and anion. Now, all of those words should be familiar to you, but you may want to pause the video here, read through the explanations and make any notes you feel you need to. Today's lesson is divided into two separate parts. So firstly, we're going to learn how to write flow charts for ion identification, and then we're going to investigate some unknown substances. So let's start with the flow charts. Flow charts are visual tools used to represent processes. They help simplify complex procedures by breaking them down into sequential steps, making them easier to understand and follow. Flow charts often consist of shapes. Each shape represents a specific part of the process. So rectangles represent processes or actions. Diamonds represent decision points and arrows represent the flow direction. So you can see an example there involving a lamp that isn't working. In chemistry, flow charts can outline many useful processes from reactions to mechanisms. So here's an example. We mix two reactants together. Is there a colour change? If there is a colour change that tells us a reaction has occurred, and we can record our results in a suitable table. If there is no colour change, we can look for fizzing or effervescence. If there's effervescence, yes, a reaction has occurred and we can record those results in the table and so on. Here, a simple flow chart demonstrates the identification process for some flame tests. So place the sample in a blue Bunsen flame. What colour does the flame turn? So we've got four potential colours here and the related ions. If it's an orange-red flame, for example, we know that calcium ions are present. We are now going to complete task A. Construct a flow chart for ion identification tests, including flame tests and aqueous cation and anions. You could do this separately or as one larger flow chart. For example, for the aqueous cation, you could start with the addition of sodium hydroxide and include the steps for identifying different metal ions based on the precipitate formation and solubility. So pause the video here and complete that activity. Welcome back. So here's a potential flow chart for flame tests, and it includes a whole variety of different flame tests colours there. So lilac for potassium, red for lithium ions, for example. So here's a potential flow chart for aqueous metal cation tests here. So adding sodium hydroxide to the sample, and then the colour of the precipitate. So if it's blue, that would be copper, two ions. If it's green, that would be iron, two ions. And if it's brown, that would be iron, three ions. And then if a white precipitate is formed, we add excess sodium hydroxide. And if the precipitate dissolves, we know it's aluminium ions present, and if it doesn't dissolve, that suggests it's calcium ions present. So here's a more complex flow diagram to show aqueous ion tests. So you might want to pause the video here and just compare that with the one that you've drawn. Now we're moving on to part two of the lesson, which is Investigating Unknown Substances. To accurately identify unknown samples is crucial to follow the correct order of ion testing. So start with dilute acid to detect carbonates as they release carbon dioxide gas. This step prevents interference in subsequent tests. Next, test for sulphates, any carbonates would've reacted already ensuring accurate results for sulphate detection. Then test for halides after acidification, do not use hydrochloric acid remember, to remove residual carbonates preventing false positives. And lastly, testing for metal cation is often completed last, as the anion tests often give clearer results. Accurate recording of observations and results is essential for reliable conclusions. We need to note all the changes such as precipitate formation, any colour changes we might see, and gas evolution. So we're looking for fizzing or effervescence. We need to make detailed observations because they're crucial for distinguishing between similar reactions and confirming results through follow-up tests. We are now going to do task B. So what I want you to do is plan and carry out a method to identify five unknown aqueous substances from the following list. So we've got calcium chloride, calcium sulphate, iron two chloride, potassium carbonate, and potassium iodide. You're gonna outline the steps, the reactants needed and the expected observations for each test. You're going to consider using the least number of tests possible by strategically planning the sequence of tests. So pause the video here, carry out your plan, and if you get the opportunity, carry out the experiment as well. Welcome back. So here are the potential materials needed and the different tests. So we've got the cation test, the halide test, the sulphate test, the carbonate test, and the flame test as well. So pause the video here, check that next to your answers and see what you've got correct. Here is a potential results table for that experiment. So we've got the results for each of the individual tests there, and then the identification of those ions and cation as a result of that. So pause the video here again and check it against your results. Here is a summary of today's lesson. Unique tests for each substance help minimise errors and ensure correct identification. Flow charts break down complex activities into ordered sets of simpler steps, crucial for efficient iron identification, observations and results should be recorded accurately for analysis during the practical. So thank you very much for joining me for today's lesson.