Chemical analysis is all about figuring out what's actually in...
Chemistry274 views·Updated 20 Aug 2026·4 pagesChemical Analysis: Key Concepts in Combined Science
Charlotte@charlotte26
1 / 4
1
of 4
Pure Substances vs Mixtures
Ever wondered why chocolate melts at a specific temperature but your mixed sweets don't? That's because pure substances contain only one element or compound, whilst mixtures are two or more different substances that aren't chemically bonded together.
The easiest way to tell them apart is through melting points. Pure substances have a sharp melting point - they melt at one exact temperature. Mixtures melt over a range of temperatures because each component melts at different points.
Formulations are special mixtures where each ingredient is carefully measured for a specific purpose. Think about medicines, paints, cleaning products, fuel, and even your favourite foods - they're all formulations designed to work perfectly for their job.
Quick Check: Next time you're cooking, notice how butter (pure fat) melts sharply whilst margarine (a formulation) melts more gradually!
2
of 4
Paper Chromatography
Paper chromatography is like giving substances a race up a piece of paper - and it's brilliant for separating things like food colourings, inks, and dyes to see what they're really made of.
Here's the method: draw a pencil line (never pen - it's insoluble!), place your ink dots on the line, then dip the paper so the line sits just above the water. As the paper absorbs the solvent, your substances race upwards at different speeds.
The mobile phase is your solvent doing the moving, whilst the stationary phase is the paper staying put. If your substance doesn't move, it's insoluble. One colour means it's pure, multiple colours reveal it's a mixture.
Lab Tip: Always use a pencil for your baseline - ink would interfere with your results and ruin the whole experiment!
3
of 4
Reading Chromatograms and Rf Values
Your chromatogram tells you loads about what you're testing. Pure substances show up as one spot, whilst impure substances create multiple spots - it's like a fingerprint for chemicals.
Rf values are your secret weapon for identifying unknown substances. Calculate them using: distance travelled by substance ÷ distance travelled by solvent. These values stay consistent for the same substance in the same solvent, so you can compare with reference tables.
Think of Rf values like a chemical ID card - they help you identify mystery substances by matching them against known chemicals.
Exam Tip: Always measure from the centre of spots to the pencil line and solvent front for accurate Rf calculations!
4
of 4
Gas Tests You Need to Know
These four gas tests are absolute exam favourites, and each has a memorable result that makes identification dead easy.
Oxygen - "relight my fire!" A glowing splint relights because oxygen supports combustion. Hydrogen gives the classic "squeaky pop" when you hold a lighted splint near the test tube opening.
Carbon dioxide makes limewater go "cloudy for carbon dioxide" - it turns milky white when you bubble the gas through calcium hydroxide solution. Chlorine bleaches damp litmus paper white because it's an acidic gas used for bleaching.
Memory Hack: These rhyming memory aids aren't just silly - they'll save you marks in your exams when you're under pressure!
We thought you’d never ask...
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Chemistry274 views·Updated 20 Aug 2026·4 pagesChemical Analysis: Key Concepts in Combined Science
Charlotte@charlotte26
Chemical analysis is all about figuring out what's actually in the substances around you - from the ink in your pen to the air you breathe. You'll learn how to identify pure substances, separate mixtures, and test for specific gases...
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Pure Substances vs Mixtures
Ever wondered why chocolate melts at a specific temperature but your mixed sweets don't? That's because pure substances contain only one element or compound, whilst mixtures are two or more different substances that aren't chemically bonded together.
The easiest way to tell them apart is through melting points. Pure substances have a sharp melting point - they melt at one exact temperature. Mixtures melt over a range of temperatures because each component melts at different points.
Formulations are special mixtures where each ingredient is carefully measured for a specific purpose. Think about medicines, paints, cleaning products, fuel, and even your favourite foods - they're all formulations designed to work perfectly for their job.
Quick Check: Next time you're cooking, notice how butter (pure fat) melts sharply whilst margarine (a formulation) melts more gradually!
2
of 4Sign up to see the content. It's free!
- Access to all documents
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By signing up you accept Terms of Service and Privacy Policy
Paper Chromatography
Paper chromatography is like giving substances a race up a piece of paper - and it's brilliant for separating things like food colourings, inks, and dyes to see what they're really made of.
Here's the method: draw a pencil line (never pen - it's insoluble!), place your ink dots on the line, then dip the paper so the line sits just above the water. As the paper absorbs the solvent, your substances race upwards at different speeds.
The mobile phase is your solvent doing the moving, whilst the stationary phase is the paper staying put. If your substance doesn't move, it's insoluble. One colour means it's pure, multiple colours reveal it's a mixture.
Lab Tip: Always use a pencil for your baseline - ink would interfere with your results and ruin the whole experiment!
3
of 4Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Reading Chromatograms and Rf Values
Your chromatogram tells you loads about what you're testing. Pure substances show up as one spot, whilst impure substances create multiple spots - it's like a fingerprint for chemicals.
Rf values are your secret weapon for identifying unknown substances. Calculate them using: distance travelled by substance ÷ distance travelled by solvent. These values stay consistent for the same substance in the same solvent, so you can compare with reference tables.
Think of Rf values like a chemical ID card - they help you identify mystery substances by matching them against known chemicals.
Exam Tip: Always measure from the centre of spots to the pencil line and solvent front for accurate Rf calculations!
4
of 4Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Gas Tests You Need to Know
These four gas tests are absolute exam favourites, and each has a memorable result that makes identification dead easy.
Oxygen - "relight my fire!" A glowing splint relights because oxygen supports combustion. Hydrogen gives the classic "squeaky pop" when you hold a lighted splint near the test tube opening.
Carbon dioxide makes limewater go "cloudy for carbon dioxide" - it turns milky white when you bubble the gas through calcium hydroxide solution. Chlorine bleaches damp litmus paper white because it's an acidic gas used for bleaching.
Memory Hack: These rhyming memory aids aren't just silly - they'll save you marks in your exams when you're under pressure!
We thought you’d never ask...
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
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Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
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