C12 Chemical Anaylsis
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what is a pure substance?
a substance which is made up of just one substance (an element or compound)
what are the fixed points of a substance?
the melting and boiling points of an element or compound
what do impurities do to the melting and boiling points of a substance?
lower the melting point increase the boiling point
what is a formulation?
a mixture that has been designed as a useful product with set proportions of substances in the mixture
what is the Rf value of a substance?
a measurement from chromatography: the distance a spot of substance has been carried above the base line divided by the distance of the solvent front
what is a positive test for hydrogen?
a lighted splint ‘pops’
what is the positive test for oxygen?
a glowing splint relights
what is a positive test for carbon dioxide gas?
limewater turns milky (cloudy white)
what is a positive test for chlorine gas?
damp blue litmus paper turns white (as it gets bleached)
what is the flame colour for lithium ions?
crimson
what is the flame colour for sodium ions?
yellow
what is the flame colour for potassium ions?
lilac
what is the flame colour for calcium ions?
orange-red
what is the flame colour for copper ions?
green
how do you carry out a flame test?
• dip a nichrome wire loop in HCl and heat it. dip it again in HCl • dip wire in metal compound being tested • hold wire in roaring blue flame of a bunsen burner • use the colour of the flame to identify the metal ion
what is a precipitate?
an insoluble solid formed by a reaction taking place in a solution
what positive metal ions produce a white precipitate when reacted with sodium hydroxide?
aluminium calcium magnesium
how can you tell that aluminium ions are in a compound when sodium hydroxide is added?
it forms a white precipitate if more sodium hydroxide is added, the precipitate dissolves
what colour precipitate is formed when copper (II) ions are present?
blue
what colour precipitate is formed when iron (II) ions are present?
green
what colour precipitate is formed when copper (III) ions are present?
brown
how do you test for carbonates?
add a dilute acid and test the gas given off using limewater to see if it is carbon dioxide
what is the test to see if halide ions are present?
add dilute nitric acid to remove carbonate ions add silver nitrate and see if a precipitate forms
what colour precipitate is formed when iodide ions (I-) are present?
yellow