8. Chemical Analysis
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What is a pure substance?
contains only one type of compound or element e.g pure water
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 has a lower mp but a higher bp
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?
mixtures that have been prepared using a specific formula so = : -precise amounts of different components -have a particular function
Examples of formulations?
Toothpaste, fuel, cleaning agents, paints, medicines, alloys, fertilisers, food+drink
whats an important feature of formulations
-different components always present in same proportions -each component contribute a different property
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
[a[er chromatography method
• draw a baseline on filter paper • add sample of ink to the pencil line • fill a beaker with a shallow amount of solvent • place filter paper in beaker -dont submerge baseline and add a lid to stop solvent evaporating • wait for solvent to seep up the paper- diff dyes will move up at different rates so will separate different substances • leave to dry
What is the mobile phase in chromatography?
the substance molecules can move in The solvent (e.g. water)
What is the stationary phase in chromatography?
material where molecules cant move The paper
how does the solubility of the substance affect the speed
substances that are more soluble = more time in mobile phase= move faster substances = less soluble= more time in stationary phase =slower
What is Rf factor?
Distance substances move up the paper in a certain amount of time
What is the solvent front?
Point at which water stops moving up the paper
how is carbon dioxide tested for
place calcium hydroxide (limewater) in a test tube bubble gas sample through calcium hydroxide if its C02 solution = cloudy
What is the baseline?
Line where original sample was placed
How is carbon dioxide tested for?
Limewater turns cloudy Hydrochloric acid + calcium carbonate
How is oxygen tested for?
place glowing splint into test tube with the sample gas if oxygen present glowing splint will relight Hydrogen peroxide -> water + oxygen
Ways to test for positive ions (cations) ?
Flame test and sodium hydroxide/precipitate test
What is the flame test?
• take a platinum wire loop, clean it in some dilute HCl, rinse in distilled water, heat over Bunsen • dip wire loop into compound you want to test • hold wire loop in clear blue part of Bunsen flame • Using the colour of the Bunsen flame to identify the metal ion in the compound