Chemical Analysis Flashcards
What is a cation?
A positively charged ion
What test is used to identify metal ions?
Flame tests
How do you carry out a flame test?
- clean a platinum wire loop by dipping it into dilute HCl and holding it into a flame
- if it burns without any colour, the you can dip it into the sample you want to test and put it back in the blue part of the Bunsen flame
What colour is formed when lithium is flame tested?
Red
What colour is formed when sodium is flame tested?
Yellow
What colour is formed when potassium is flame tested?
Lilac
What colour is formed when calcium is flame tested?
Orange-red
What colour is formed when copper is flame tested?
Blue-green
Describe tests for Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution
Many metal hydroxides are insoluble and leave a precipitate, some of these have a distinctive colour. To test for this, add sodium hydroxide solution to the compound.
Cu2+ leaves a blue precipitate
Fe2+ leaves a sludgy green precipitate
Fe3+ leaves a red-brown precipitate
Describe the test for NH4+ using sodium hydroxide
Add sodium hydroxide to solution and if damp red litmus paper turns blue (gas given off), then ammonia is present and the solution contained ammonium. (Litmus paper must be damp so that gas can dissolve and make the colour change)
What is an anion?
A negative ion
Describe the test for carbonates
Add dilute HCl to sample, if carbonates are present then CO2 will be released (test with lime water)
Carbonate + acid -> carbon dioxide + water
CO3 + 2H ->CO2 + H20
Describe the test for Cl-, Br- and I-
To test for chlorine, bromine and iodine ions add dilute nitric acid followed by silver nitrate solution (acidified silver nitrate solution). Acid is added to get rid of carbonate or sulfate ions as these would give a precipitate and affect results.
Chloride will give a white precipitate of silver chloride
Bromide will give a cream precipitate of silver bromide
Iodide will give a yellow precipitate of silver iodide
Describe the test for sulfate ions
Add dilute HCl and barium chloride solution to sample (acidified barium chloride). A white precipitate means sulfate ions are present
What is the test for chlorine?
Bleaches damp blue litmus paper white
What is the test for oxygen?
Relights a glowing splint/spill
What is the test for carbon dioxide?
Turns limewater cloudy
What is the test for hydrogen?
Makes a squeaky pop sound with a lighted splint (H burns with O to form H2O)
What is the test for ammonia?
Ammonia turn damp red litmus paper blue and smells
What is the test for water using anhydrous copper sulfate?
Add sample to anhydrous copper sulfate and if white powder turns blue to form hydrated copper sulfate then water is present. This tells you if water is present but not if it’s pure.
What is the physical test for pure water?
Freeze and boil sample while recording the freezing and boiling points. If these aren’t 0 and 100°C, then the sample is not pure water. This is because a pure sample of water has defined physical properties including its fpt and bpt
