Combined Chemistry - 5.8
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What is the chemical meaning of a ‘pure’ substance? What is the every day meaning of a ‘pure’ substance?
In Chemistry: A single element or compound that is not mixed with any other substance. In everyday language: A substance that hasn’t had anything added to it, e.g. pure milk.
What data can be used to prove a substance is ‘pure’ and not a mixture?
Melting and Boiling points (because pure substance melt and boil at specific temperatures)
What is a formulation?
A mixture that has been designed as a useful product.
Give three examples of formulations
Any three from: Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
Name the two phases in chromatography.
• Stationary Phase • Mobile Phase
In Chromatography, how do you calculate the Rf value for a substance?
Rf = distance moved by substance / distance moved by solvent
What will the chromatogram of a pure substance look like?
A pure substance will only show a single spot on the chromatogram.
Explain how paper chromatography can be used to separate a mixture.
• A substance is added to the chromatography paper (stationary phase). • Molecules within a substance dissolve in the solvent and move up the paper (mobile phase). • The molecules within the substance separate because different chemicals spend different amounts of time in the mobile and stationary phases and therefore move different distances up the paper.
Describe how you would test for Hydrogen.
• Collect gas in a test tube • Hold a burning splint at the open end of a test tube. • You will hear a ‘pop’ sound if Hydrogen is present
Describe how you would test for Oxygen.
• Collect gas in a test tube • Insert a glowing splint into the test tube • The splint will relight if oxygen is present
Describe the test for Carbon dioxide.
• Bubble the gas through limewater (calcium hydroxide solution) • If the limewater turns milky (cloudy) then carbon dioxide is present
Describe the test for Chlorine.
• Collect gas in a test tube • Place damp litmus paper in the test tube • If chlorine is present, the litmus paper is bleached and turns white