Further Analysis Flashcards
Pure substance
A single element or compound not mixed with any substance
Formulation
A mixture of substances designed to be a useful product
Impure substance
A substance that contains other substances (impurities)
How to identify pure vs impure substance
A pure substance has a fixed melting and boiling point. An impure substance has a range of temperatures.
Hydrogen gas test
Lit splint in test tube → gas burns with squeaky pop
CO2 test
Bubble gas through limewater → White prep
Cl test
Damp blue litmus paper → Bleaches
Alkene
Bromine water → Orange to colourless
Acid/Alkali
Indicators colour change
pH
Universal indicator → colour change
Acid
Add metal carbonate
Bubble gas through limewater
If CO2 produced goes cloudy
Excited electrons
- When provided with energy, electrons are promoted to higher energy levels in the atom, e.g. thermal energy
- They then drop down to ground state, releasing energy.
Why do excited electrons produce light
- Different atoms have different electron arrangements, giving off different light frequencies.
- Some frequencies are in the visible region of the EM spectrum.
Li+ (flame)
Crimson
Na+ (flame)
Yellow
K+ (flame)
Lilac
Ca 2+ (flame)
Orange/Red
Cu 2+ (flame)
Green
Limitations of flame tests for identifying ions
- Some colours of flame are hard to tell from their background
- Some metals give similar colours of flame
- Some metals give no flame colour as the frequency they give off is not in visible light e.g. UV rays or Infrared
A mixture of metals will give a mixture of colours. One colour may mask the others.
Al 3+ NaOH
White
Ca 2+ NaOH
White
Mg 2+ NaOH
White
Cu 2+ NaOH
Blue
Fe 2+ NaOH
Green
Fe 3+ NaOH
Brown
Stationary phase
Paper
Mobile phase
Water
Separates chemicals based on the
Solubility of components.
The more soluble it is, the more it moves across the chromatogram in a given time.
Rf values from chromatographs
Distance chemical moves /
Distance solvent moves
Rf values to draw conclusions about substances
- Pure substances will show one result per chemical.
- Mixtures will show more than one.
- Identical chemicals will move at the same rate. → The retention factor (proportion of the chromatograph they cover) will be the same.
Carbonate ions
Add a dilute acid → Effervescence
MUST BE DONE FIRST. CARBONATES GIVE FALSE POSITIVE RESULTS.
Sulfate ions
Add HCl to check for no CO
Add BaCl → White precipitate
Halide ions
Add HNO3 to check for no CO
Silver nitrate
(dissolves in dilute NH4OH)
Cl-
Br-
I-
White
Cream
Yellow
Flame emission spectroscopy description
Mechanical methods to scan individual frequencies of light
Advantages of flame spectrometry
Even tiny quantities of metal can be identified
Mixtures can be analysed and compared to known spectra to identify the contents
Uses
Detection of trace elements
Determining the composition of stars
Qualitative chemical tests
Simple
Inaccurate
Requires larger samples
Instrumental tests
Rapid
Sensitive
Accurate
Expensive
- Describe why qualitative may be used over instrumental
Simpler and less expensive
Mass spectrometer
Reports relative mass of compounds
Separates mixture by compounds so that they can be identified and gives their concentration
