Tests for Ions (2) Flashcards
What is a
flame test used for?
and what does this involve?
to test for various metal ions
this involves putting the substance in a flame and seeing what colour the flame goes
What is the colour of
lithium ions
in a flame test?
crimson red flame
What is the colour of
sodium ions
in a flame test?
yellow flame
What is the colour of
potassium ions
in a flame test?
lilac flame
What is the colour of
calcium ions
in a flame test?
orange-red flame
What is the colour of
copper ions
in a flame test?
blue-green flame
Describe how you would carry out a
flame test.
(4 steps)
- Clean a nichrome wire loop by dipping it in some hydrochloric acid and the rinsing it with distilled water.
- Dip the loop into the sample you want to test.
- Put it into the clear blue part of a bunsen burner flame.
- Record the colour of the flame.
Describe how you would carry out a
precipitation reaction.
(to determine the metal present in a substance) (2 steps)
- Add a few drops of sodium hydroxide to a solution of the substance you are testing.
- If a coloured insoluble hydroxide forms, you can determine which metal was in the compound.
What is the colour of
calcium hydroxide?
(from a precipitation reaction)
white
it does not redissolve in excess
What is the colour of
copper hydroxide?
(from a precipitation reaction)
blue
What is the colour of
iron(II) hydroxide?
(from a precipitation reaction)
green
What is the colour of
iron (III) copper hydroxide?
(from a precipitation reaction)
brown
What is the colour of
aluminium hydroxide?
(from a precipitation reaction)
white
it does redissolves in excess
Describe a
test for ammonium ions.
(in solution)
- Add some sodium hydroxide solution to a solution of your substance and gently heat it.
- Hold a piece of damp red litmus paper over the test tube.
- If ammonium is present, ammonia gas will react with this and the litmus paper will turn blue.
How could you
test for carbonate ions?
(in solution) (3 steps)
- Add a couple of drops of dilute acid to a test tube containing the substance.
- Bubble the gas produced through limewater.
- If the limewater turns cloudy then carbonate ions were present.
How would you test for
halide ions?
(in solution)
Add dilute nitric acid, followed by silver nitrate solution.
(The nitric acid is added to get rid of any carbonate impurities.)
A chloride gives a white precipitate of silver chloride.
A bromide gives a cream precipitate of silver bromide.
An iodide gives a yellow precipitate of silver iodide.
How would you test for
sulfate ions?
(in solution)
- Add some dilute hydrochloric acid to the test sample.
- Add some barium chloride solution.
- If there are sulfate ions in the solution, a white precipitate of barium sulfate will form.
the hydrochloric acid is added to remove any carbonate impurities
What is
flame photometry?
an instrumental method that allows you to identify ions in a dilute solution
Describe and explain how
flame photometry works.
- A sample is placed in a flame.
- As the ions heat up their electrons become excited.
- When the electrons drop back to their original energy levels, they transfer energy as light.
- The light passes through a spectroscope, which can detect differen wavelengths of light, to produce a line spectrum.
Since no two ions have the same charge and same electron arrangement, different ions emit different wavelengths of light. So each ion produces a different pattern of wavelengths and has a different line spectrum.
What are some advantages of using
instrumental analysis?
(tests that use machines) (3)
- very sensitive - can detect even the tiniest amounts of something
- very fast - can be automated which speeds up the process
- very accurate - don’t involve human error
What is a specific positive of
flame photometry over flame tests?
flame photometry can identify a mixture of ions in a solution
