What is being taught lesson by lesson:
- Pure substances and how to test purity.
- Formulations including examples and the importance of accuracy.
- Chromatography and calculating Rf values.
- Required practical – chromatography.
- Testing for gases – CO2, H2, Cl2, O2.
Key Terms for this topic (Tier 3 vocabulary)
Purity – formulation – chromatography – stationary phase – mobile phase – pigment – solvent.
Are you ready for your assessment in this topic? Try out this simple quiz.
What everyone needs to know:
Pure substances contain only a single element or compound. Don’t get these mixed up with commercial purity. Pure orange juice is not chemically pure because it contains lots of different compounds.
Formulations are precise mixtures such as medicines, paints, alloys and cleaning products.
Chromatography is used to separate pigments that are in inks and food colouring. The solvent used is the mobile phase and the paper is the stationary phase. You need to be able to calculate Rf values (divide the distance the substance moved by the distance the solvent moved) and compare which pigments are in a colouring/ink.
Required practical 12 – Use chromatography to separate the pigments in a coloured substance. Calculate the Rf value of a range of pigments.
You need to be able to describe the tests for 4 common gases and state what a positive result for each is:
- Oxygen – relights a glowing splint
- Hydrogen – when lit produces a squeaky pop
- Carbon dioxide – turns limewater milky
- Chlorine – bleaches damp blue litmus white
Extra topics needed for the Higher papers:
In this topic, there is nothing extra for the higher papers, the questions will just be more challenging.