Chemical Analysis Flashcards
What is a pure substance?
A pure substance is a single element or compound, not mixed with any other substance
What is a formulation and how is it made?
- a formulation is a mixture of compounds in measured quantities that has been designed as an useful product
- formulation include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
- e.g. alloys are mixtures of metals; they are harder than pure metals, so have a particular purpose
Describe paper chromatography
- a start line is drawn near the bottom of the paper. The mixture is spotted on the line
- a beaker is filled with small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)
- paper is hung on a rod and placed in a beaker
- solvent travels up the paper, thus separating the components
- before solvent level reaches the end, the paper is taken out and the finish line is marked, the paper is dried
- the procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent
What is the stationary phase in chromatography?
the absorbent paper
What is the mobile phase in chromatography?
A solvent
How is Rf calculated?
Distance moved by the spot / distance moved by the solvent
Describe the test for hydrogen
Pop with burning splints over gas
Describe the test for oxygen
Glowing splint relights
Describe the test for carbon dioxide
Turns limewater milky
Describe the test for chlorine
Bleaches damp litmus paper and makes it white
Describe the flame test results
Lithium compounds -> crimson red flame
Sodium compounds -> yellow flame
Potassium compounds -> lilac flame
Calcium compounds -> orange red flame
Copper compounds -> green flame
Describe the sodium hydroxide test results
Copper(II) forms a blue precipitate
Iron(II) forms a dirty green precipitate
Iron(III) forms a brown precipitate
Al(3+), Ca(2+) and Mg(2+) form white precipitate but only the Al(OH)3 dissolves in excess NaOH to form a colourless solution
Describe the test for carbonate anions
Add dilute acid e.g. HCl
Fizzing observed, as CO2 is released
Describe the test for sulfate anions
Add a solution containing Ba(2+) cations e.g. a solution of BaCl2
White precipitate of BaSo4 forms
(!!!) can also be though of a test for barium (II); add sulfates - white precipitate forms
Describe silver nitrate tests
Add a solution of AgNo3
- chloride -> white precipitate, silver chloride
- bromide -> cream precipitate, silver bromide
- iodides -> yellow precipitate, silver iodide
What are instrumental methods?
They are accurate, sensitive and rapid methods which are useful when the amount of sample is very small
Describe the flame emission spectroscopy
- instrumental method used for identifying metal ions in solution or measuring their concentration
- spectroscope measures the exact wavelength of the light emitted by a metal ion
- that allows for definite identification -> sometimes colour are difficult to distinguish
- concentration are found by measuring the intensity of light emitted. The more intense light, the greater the concentration of the metal ion in a solution
- from the intensity vs concentration graph, you can read off a relevant concentration value at a given intensity
What are cations?
Positive ions
What are anions.
Negative ions
What is mixture?
A combination of two or more substances that aren’t chemically combined
What is a formulation?
A mixture that has been designed for a specific purpose
What is the melting/boiling point of pure substance?
A single defined temperature
What are what is the melting/boiling point of mixtures?
A range of temperatures
What is the melting point of pure water?
0 °C
What is the boiling point of pure water?
100 °C
What are some examples of formulations?
Paint, processed food, fuels, cleaning products and cosmetics
What is the test for purity?
Test melting/boiling point
What are nanoparticles?
Lumps of substance that are 1-100 nanometers in size
What are nanoparticles in formulations?
Useful in formulation as you can use less
How do you test you see if water is pure?
Test of boiling point is exactly 100 °C
What is the flame test?
A method of identifying a metal ion by the colour it produces in a roaring flame
What is the test for halide ions?
Add nitric acid and silver nitrate solution
What does precipitate mean?
An insoluble solid that forms from a solution during a chemical reaction
What are the advantages of instrumental methods?
- accurate
- sensitive
- rapid
What are the disadvantages of instrumental methods?
- expensive
- require training
- must compare results to known samples
What are the advantages of flame emission spectroscopy?
- can spot multiple ions
- can find ion concentration
