Chapter 8 - Chemical Analysis Flashcards
What do we use flame tests for?
To determine what metal ions are in a metal compound
What is the flame test method?
- Put Nichrome wire in the acid
- Put looped end into chemical you are testing
- Put loop into the hottest part of a roaring blue flame
- Observe colour change
- Clean wire by dipping in acid and checking no colour is produced in the flame before repeating with other chemicals
Lithium (Li+) Flame Colour
Crimson
-crimson lipstick - lipstick for lithium
Sodium (Na+) Flame Colour
Yellow
-sodium = so damn loud > YELLow
Potassium (K+) Flame Colour
Lilac
-lilac flowers in pots - pots = potassium
Calcium (Ca2+) Flame Colour
Orange-red
-CALum Scott is so hot - hot connotes red
Copper (Cu2+) Flame Colour
Green
Why do the flames have colours?
When heated the electrons jump to another energy level (shell) as they have more energy. As they fall back to their original energy level, the energy is emitted as a light wavelength.
What do we use a flame emission spectroscope for?
To use to produce a line emission spectra which shows what colour is given off at specific energy levels
What are the advantages of using instrumental methods over a flame test?
- more accurate
- higher sensitivity
- faster
What is the graph that is used to find the concentration of ions called?
Calibration curve
Practical: Adding NaOH - what is the method?
- Dissolve solid sample in distilled water
- Put solution into test tube (about 2cm depth)
- Add NaOH drop by drop
- Mix after each drop and check for any precipitate
What happens when you add NaOH to aqueous Cu2+?
Light blue precipitate formed
What happens when you add NaOH to aqueous Fe2+?
Green precipitate - slowly turns brown
What happens when you add NaOH to aqueous Fe3+?
Reddish-brown precipitate formed
If no precipitate is formed when NaOH is added, what do we do to test for ammonia ions?
Warm the solution
If ammonia present:
-Gives off NH3 smell
-Turns litmus paper blue
What happens when you add NaOH to aqueous non-transition metals e.g. Al3+ Ca2+ and Mg2+?
White precipitate formed
How can we differentiate between Al3+ Ca2+ and Mg2+?
Add more NaOH
If the precipitate dissolves then it is Al3+
If it does not dissolve either Ca2+ or Mg2+ are present
What is the gas test for hydrogen?
Put a lit splint in a test tube and if hydrogen is present there will be a squeaky pop
What is the gas test for oxygen?
If a glowing splint relights oxygen is present
What is the gas test for chlorine?
Use damp litmus paper. If chlorine is present it will bleach the litmus and turn it from blue to white
What is the gas test for carbon dioxide?
Bubble through limewater and if carbon dioxide is present it well turn from colourless to cloudy/milky
Define pure in chemical terms
Only one type of element / compound with no other substance
What is a formulation?
A mixture that has been designed as a useful product e.g. fuels, medicines, paints and cleaning agents
What can be used to identify if something is pure or impure?
Melting or boiling point
What is the equation for finding the retention factor during chromatography?
Rf = distance of spot from baseline/distance of solvent from baseline
Rf < or = 1
What is chromatography used for?
To separate mixtures of colours
What is the method for testing for carbonate ions?
- Dissolve carbonate in water
- Add dilute HCl (it will fizz)
- Use bung to capture gas and transport gas through delivery tube to be bubbled through limewater
- Limewater turns milky/cloudy if CO2 is present.
What is the method for testing for halide ions?
- Dissolve halide in water
- Add dilute nitric acid
- Add silver nitrate drop by drop
- If precipitate forms observe the colour
What colour precipitate does chlorine form?
White
What colour precipitate does bromine form?
Cream
What colour precipitate does iodine form?
Yellow
What is the method for testing for sulfate ions?
- Dissolve sulfate in water
- Add dilute HCl (won’t fizz)
- Add barium chloride [TOXIC] drop by drop
- If dense white precipitate forms (barium sulfate) sulfate ions are present
