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I can conduct ion identification tests using flow charts, accurately record observations, and identify gases to ensure correct and safe lab practices.

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Licence

This content is © Oak National Academy Limited (2023), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Key learning points

Unique tests for each substance help minimise errors and ensure correct identification.
Gas tests can be used to identify carbon dioxide, oxygen, hydrogen and ammonia.
Observations and results should be recorded accurately for analysis during the practical.
Flow charts break down complex activities into ordered sets of simpler steps, crucial for efficient ion identification.

Common misconception

All tests for ions are interchangeable and can be used in any order without affecting the outcome.

Clarify that each test is specific and must be conducted in a particular order to avoid interference. For example, testing for sulfates before halides can prevent false positives caused by overlapping precipitates, ensuring accurate identification.

Keywords

Precipitate - An insoluble solid formed when two solutions react together.
Ion - An ion is an atom or group of atoms with a positive or negative charge due to the loss or gain of electrons.
Cation - A positively charged ion.
Anion - A negatively charged ion.

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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, 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 has two parts, ion identification flow chart, and investigating unknown substances.

So let's start with the first part of today's lesson, the identification of ions using 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 cations, 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 test colours there.

So lilac for potassium, red for lithium ions for example.

Here we have the flow chart for aqueous metal cation tests.

We've added sodium hydroxide to the sample, and we need to see what colour precipitate forms. So if it's a blue precipitate that suggests copper II, ions, green precipitate would be iron II ions, brown precipitate would be iron III ions.

And if a white precipitate is formed, then we need to see if it dissolves in excess sodium hydroxide.

And if it does dissolve in excess sodium hydroxide, then we know aluminium ions are present.

And if it doesn't, we know either calcium ions or magnesium ions are present.

And that's where we would carry out a flame test.

And the flame test would tell us if it was red orange that calcium ions have been produced.

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.

We're now moving on to the second part of today's lesson, investigating unknown substances.

To accurately identify unknown samples, it 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 cations 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 II chloride, potassium carbonate, and potassium iodide.

You're going to 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 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 anions and cations 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 ion 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.

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