C12- Chemical analysis
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What is a pure substance? Example? What is a mixture? Example?
A compound or element that only contains one substance Pure water (just H2O) Two or more substances that aren’t chemically combined Air
Key fact about pure substances? Key fact about impure substances?
They have specific melting and boiling points and will melt/boil at exactly that temp They will melt/boil over a range of temps
What are fixed points?
The melting and boiling points of a substance
How does rock salt help roads become less slippery? How does salt help when cooking?
Lowers the melting point of water, the impurities disrupt the structure of ice, weakens intermolecular forces, less ice Raises the boiling point of water, food cooks more quickly
Formulation? 2 Examples?
A mixture designed to create a useful product. Measured in fixed proportions to create specific properties Paint, washing up liquid
Paper chromatography definition?
The separation of substances using a solvent which carries the mixture through paper
Chromatography Stationary phase? Mobile phase?
The fixed surface where the process takes place (filter paper) The solvent that carries the dissolves substances (solvent)
From a chromatogram What dyes are in the mixture? How many substances it contains?
Contain dyes that travelled the same distance and have the same colour The number of spots in the same column
How to calculate the Rf value and what is it?
Retention factor = distance travelled by substance / distance travelled by solvent The ratio of the distance a substance travels
What does a higher Rf mean? What does a lower Rf mean? When will Rf change?
Substance is more attracted to solvent, spends more time in the solvent Substance is more attracted to paper, spends less time in the solvent The solvent and paper used
Paper chromatography method?
-Draw pencil line 2 cm from bottom of the filter paper -Put a small dot of each dye spaced apart on the pencil line and label -Place small amount of water in a beaker -Place filter paper in the solvent so the water is just below the dyes -Leave for 5 mins, label solvent front and measure using a ruler, dry -Calculate Rf values using Rf= distance moved by substance / distance moved by solvent
Test for hydrogen? Oxygen? Carbon dioxide? Chlorine?
Lit splint–>squeaky pop sound Glowing splint–>splint relights Bubble through limewater–>turns cloudy Damp litmus paper–>turns white/bleached
False positive
When a positive outcome of a test occurs but not from the substance you are testing for
How to carry out flame test
Dip clean wire loop into compound being tested. Place it in blue bunsen flame. Observe and record flame colour
How to identify positive (metal) ions of group 1 metals?
Dissolve in water, add sodium hydroxide solution. No precipitate will form. Carry out flame test. Lithium ions present = crimson flame. Sodium ions present = yellow flame. Potassium ions present = lilac flame.
How to identify positive (metal) ions of Group 2 metals?
Dissolve in water, add sodium hydroxide solution. White precipitate forms. Add excess sodium hydroxide. Precipitate doesn’t dissolve. Carry out flame test. Calcium ions present = orange-red flame. Magnesium ions present = no colour.
How to identify positive (metal) ions of a Group 3 metal?
Dissolve in water, add sodium hydroxide solution. White precipitate forms. Add excess sodium hydroxide. Precipitate dissolves. Aluminium ions present.
How to identify positive (metal) ions of transition metals?
Dissolve in water, add sodium hydroxide solution. Forms coloured precipitate. Copper (II) ions present = blue precipitate, then green flame in flame test. Iron (II) ions present = green precipitate, turns brown if left in air. Iron (III) ions present = brown precipitate.
How to identify negative (non-metal) ions of Group 7?
Dissolve in water, add nitric acid. No fizzing occurs. Add barium nitrate. No precipitate formed. Add acidified silver nitrate to new sample. Precipitate formed. Chloride ions present = white precipitate. Bromide ions present = cream precipitate. Iodide ions present = yellow precipitate.
How to identify negative (non-metal) ions of carbonate and sulfate?
Dissolve in water, add nitric acid. Fizzing occurs. Carbonate ions present. Dissolve in water. Add nitric acid. No fizzing. Add barium nitrate. White precipitate formed. Sulfate ions present.
Ionic equations for positive ion precipitates formed? e.g Group 2 metals, Group 3 metal, transition metals And the colour?
Mg2+ +2OH- –> Mg(OH)2 white Ca2+ +2OH- –> Ca(OH)2 white Al3+ +3OH- –> Al(OH)3 white Fe2+ +2OH- –> Fe(OH)2 green Fe3+ +3OH- –> Fe(OH)3 brown Cu2+ +2OH- –> Cu(OH)2 blue
Ionic equations for negative ion precipitates formed? e.g sulfate, group 7 non-metals And the colour?
SO4 2- + Ba2+ –>BaSO4 white Cl- + Ag+ –> AgCl white Br- + Ag+ –> AgBr cream I- + Ag+ –> AgI yellow
Method to show a sample of calcium bromide solution. With ionic equations for precipitates formed.
Dissolve in water, split in three test tubes. In one, add sodium hydroxide, forms white precipitate. Ca2+ +2OH- –> Ca(OH)2. Add excess sodium hydroxide, precipitate doesn’t dissolve. Dip clean wire loop into solution, place in blue bunsen burner flame. Will turn orange-red, calcium ions present. In other test tube, add nitric acid, no fizzing will occur. Add barium nitrate, no precipitate will form. In a third test tube, add silver nitrate, cream precipitate forms. Br- + Ag+ –> BrAg. Bromide ions present.
Instrumental methods Example? Ads and dis?
Flame emission spectroscopy Ads- Sensitive, only need a small amount of the sample; quicker Dis- Expensive, requires special training to use