8. Chemical Analysis
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What is a pure substance?
Made up of just one substance - either an element or a compound
How are properties changed when impurities are introduced?
• conductivity • strength • melting and boiling point
What happens when salt is added to pure water?
The salt dissolve to produce an impure substance (salt lowers the temperature of ice) so melts the ice
Difference between melting/boiling point between pure and impure substances?
Pure substances melt at a specific temperature whereas impure substances can melt or boil at a range of temperatures
How does melting point of an impure substance compare to that of a pure one?
Impure substances have lower melting points than pure substances
What is a formulation?
A mixture of compounds/substances that do not react with each other but produce a mixture to suit a particular use
Examples of formulations?
Toothpaste, moisturiser, make up, alloys, paint, medicines
What does pure mean in advertising?
Nothing else has been added to the product
What are some different types of food additives?
Preservatives, colourings, flavour enhancers
What is chromatography?
A technique for separating mixtures into their components in order to analyse, identify, purify the mixture or components
What is the mobile phase in chromatography?
The solvent (e.g. water)
What is the stationary phase in chromatography?
The paper
What is Rf factor?
Distance substances move up the paper in a certain amount of time
How to work out Rf factor?
Distance moved by substance / distance moved by solvent
What is the solvent front?
Point at which water stops moving up the paper
What is the centre spot?
Point at which a band or spot of colour is
What is the baseline?
Line where original sample was placed
How is chlorine tested for?
Electrolysis
How is carbon dioxide tested for?
Limewater turns cloudy Hydrochloric acid + calcium carbonate
How is oxygen tested for?
Glowing splint relights Hydrogen peroxide -> water + oxygen
How is hydrogen tested for?
Squeaky pop test Mg + HCl -> MgCl + H2
Ways to test for positive ions?
Flame test and sodium hydroxide/precipitate test
What is the flame test?
Using the colour of the Bunsen flame to identify the metal ion in the compound
What does a crimson flame show?
Lithium present