Chemical Analysis Flashcards
What is a pure substance?
Single element or compound not mixed with any other substance which melt and boil at specific temperatures
What is an impure substance?
Contains more than one element or compound in a mixture.
Melts and boils at a range of temperatures
What are formulations?
Examples of mixtures which have many different components in very specific proportions to make them useful as fuel, cleaning agents, paints, alloys, fertilisers and foods
What is the mobile phase?
The solvent which must be below the pencil line or the substances will be dissolved away from the paper
What does it mean if the substance travels a long way up the paper?
It is more soluble
What does it mean if the substance only produces one spot?
The substance is pure
What is the solvent front?
The top of where the solvent travels to up the paper
What is the stationary phase?
The paper
What is chromatography?
A method to separate different components in a mixture
What is the Rf value?
Distance moved by substance divided by distance moved by solvent
How do you test for cations?
Sodium hydroxide solution is added to the substance
Positive test for Al3+
White precipitate which dissolves in excess of
Positive test for Ca2+
White precipitate does not dissolve
Positive test for Mg2+
White precipitate does not dissolve
Positive test for Cu2+
Blue precipitate
Positive test for Fe2+
Green precipitate
Positive test for Fe3+
Brown precipitate
How do you test for a carbonate CO3 2-?
Add dilute (hydrochloric) acid and test with limewater
How do you test for sulfates?
Add barium chloride solution in the presence of hydrochloric acid and you should see a white precipitate form
How do you test for halide ions?
Silver nitrate solution and nitric acid
Positive test for Cl-
White precipitate
Positive test for I-
Yellow precipitate
Positive test for Br-
Cream precipitate
Why does a flame test not work if there is more than one metal in the substance?
The colours mix and intense colours mask more subtle colours
Lithium flame colour
Crimson
Sodium flame colour
Yellow
Potassium flame colour
Lilac
Calcium flame colour
Orange red
Copper flame colour
Green
What is instrumental analysis?
Involves complex scientific equipment to test substances
Rapid
Accurate
Sensitive
What is flame emission spectroscopy?
Instrumental method to test for metal ions
Sample solution is put into flame and the light given off is passed through a spectroscope
The instrument tells you the exact wavelength of light being given off as a line spectrum
Compare spectrum to reference
You can also measure concentration of substance
