C12 - Chemical Analysis - Complete Flashcards
What is meant by purity in chemistry and how does this differ from in commercial cases?
In commercial cases, ‘pure’ means nothing added to it, whereas in chemistry ‘pure’ means solely one substance. This substance can be a compound or element, but not a mixture.
How can you separate different substances?
By testing them at their boiling and melting points
What do impurities tend to do to a substance?
Lower its melting point and raise its boiling point
What is formulation?
A mixture that has been designed to produce a useful product
Give two examples of formulations
Paint, drugs, washing-up liquids, fuels, alloys, pesticides, cosmetics and food products
How do you detect amino acids in a chromatogram since they are colourless?
You spray it with a locating agent and they will turn purple
What differs in chromatography that separates the substances?
The amounts of attraction to the paper and the solvent that separates them differs: allowing the mixtures to be separated into many different fractions
Why is retention factor used?
So that different substances can be compared and identified with each other on a database, were it would impractical to store pictures or actual chromatograms to compare
What is the equation for retention factor?
Retention factor = distance moved by substance / distance moved by solvent
How must you keep the chromatography experiments the same each time?
They must be at the same temperature and with the same solvent each time
Why can’t you test a mixture of metal ions with a flame test?
As one of their colours may be masked by the other ions
What false must you use for flame tests?
Roaring blue flame
What precautions must be taken with the nichrome wire loop before you use it for a flame test?
It must be dipped in hydrochloric acid before into the substance, and then heated to get rid of any contamination, and then dipped into he hydrochloric acid again before into the substance
What three ions form a white precipitate with sodium hydroxide?
Mg 2+, Ca 2+ and Al 3+
How do you distinguish between the 3 white precipitates formed by sodium hydroxide?
Aluminium dissolves if more sodium hydroxide is added, and then the other two can be distinguished by a flame test - magnesium gives no colour and calcium gives a brick red
What colour precipitate is formed when sodium hydroxide is added to Copper (II) ions?
Blue
What colour precipitate is formed when sodium hydroxide is added to Iron (II) ions?
Green
What colour precipitate is formed when sodium hydroxide is added to Iron (III) ions?
Reddish brown
What colour do Potassium ions give in a flame test?
Lilac
What colour do Lithium ions give in a flame test?
Crimson red
What colour do Calcium ions give in a flame test?
Brick red
What colour do Sodium ions give in a flame test?
Yellow
What colour do Copper ions give in a flame test?
Green
How can you test for a carbonate?
You add dilute acid to it and it produces carbon dioxide
Why does CO2 turn limewater milky?
As the acidic carbon dioxide reacts with the alkaline sodium hydroxide in the limewater - creating a white precipitate: turning it milky
How do you test for the halides?
First you add dilute nitric acid, and then you add silver nitrate. If a precipitate forms, halide ions are present
What are the halides?
Chlorides, bromides and iodides
Which precipitate do iodide ions create in dilute nitric acid and silver nitrate?
Yellow
Which precipitate do chloride ions create in dilute nitric acid and silver nitrate?
White
Which precipitate do bromide ions create in dilute nitric acid and silver nitrate?
Cream
How can you test for a sulphate in a solution?
Add dilute hydrochloric acid and then barium chloride. If the precipitate is white, a sulphate is present
Why do you add dilute hydrochloric acid before the barium chloride when you test for sulphates?
So that any carbonate ions that are present that would otherwise react with the barium
What are 2 benefits of modern instrumental methods?
They are faster / They are more accurate and sensitive / They enable tiny samples to be analysed
What are 2 negatives of modern instrumental methods?
They are often very expensive / They take special training to use / They give results that can often be interpreted in comparison with known substances
How does flame emission spectroscopy work?
When the different metal ions are heated, their electrons become excited and jump energy levels. When they return to their original level, the energy is released as light. Flame emission spectroscopy analyses the wavelengths of this light and uses them to compare to a database of existing results. By doing so, it can find what ion was burned and in what concentration it was
Give one example of where flame emission spectroscopy is used
In the steel industry, where the amounts of each particle present in the alloy must be monitored carefully / In large water companies to make sure the water they are providing is safe
