Qualitative Analysis Flashcards
How would you carry out a flame test?
Clean a nichrome wire loop by dipping it into hydrochloric acid then rinsing it in distilled water. Dip the wire into a sample of the compound and put the loop into a clear blue Bunsen flame. Record the colour
What colour does lithium turn in a flame test?
Crimson red
What colour does sodium turn in a flame test?
Yellow
What colour does potassium turn in a flame test?
Lilac
What colour does calcium turn in a flame test?
Orange red
What colour does copper turn in a flame test?
Blue green
How would you carry out a sodium hydroxide test?
Add a few drops of sodium hydroxide solution to a solution of the compound. If a hydroxide precipitate forms, you can use the colour to determine the metal ion in the compound
What colour does aluminium make in a sodium hydroxide test?
White at first, but then redissolved in excess sodium hydroxide to form a colourless solution
What colour does calcium make in a sodium hydroxide test?
White
What colour does copper make in a sodium hydroxide test?
Blue
What colour does iron(II) make in a sodium hydroxide test?
Green
What colour does iron(III) make in a sodium hydroxide test?
Brown
What do ammonium ions produce in sodium hydroxide solution?
When you gently heat it it gives off ammonia gas. You can test for this by holding a piece of damp red litmus paper over it. Ammonia gas will turn it blue.
How do you test for halide ions?
Add some dilute nitric acid followed by a few drops of silver nitrate solution. Chloride, bromide, and iodide ions all give different colour precipitates
What colour precipitate does chloride form in silver nitrate solution?
White
What colour precipitate does bromide form in silver nitrate solution?
Cream
What colour precipitate does iodide form in silver nitrate solution?
Yellow
How do you test for carbonates?
To test for carbonate ions add some dilute acids. If they are present the mixture will fizz as the carbonate reacts with the acid to produce carbon dioxide gas:
Carbonate ions + acid –> carbon dioxide + water
You can use the limewater test to see if it is carbon dioxide
How do you test for sulphate ions?
Add some dilute hydrochloric acid to the test sample to stop any precipitate reactions not involving sulphate ions from taking place. Then add some barium chloride solution. If sulphate ions are present a white precipitate of barium sulphate will form.
Barium ions + sulphate ions –> barium sulphate
What is flame photometry?
An instrumental method that allows you to identify ions in a dilute solution. Each ion produces a unique line spectrum with different lines in different places. The intensity of the wavelengths indicates the concentration. It also works for mixtures of ions
What are some advantages of using machines to test unknown substances?
They are very sensitive so can detect the tiniest amounts of substances
They are very fast and tests can be automated
They are very accurate and do not involve human error
