Qualitive Analysis Flashcards
What are flame tests used for?
To identify metal ions in substances
How to carry out a flame test?
- Light Bunsen Burner and open air hole to give hot blue flame
- Pick up small smaple using wire loop
- Hold sample in edge of flame and observe and record flame colour
What is used to clean the wire loop?
Hydrochloric acid
Why is platinum used for the wire loop?
Has a high melting point, is unreactive and gives no colour to the flame
What is normally used instead of platinum for the wire loop?
Nichrome alloy because although it produces faint orange colour in flame, it is much cheaper
What are the different colours produced by these different cations?…
- Lithium
- Sodium
- Potassium
- Calcium
- Copper
- Iron (II)
- Iron (III)
Li+ = red Na+ = yellow K+ = lilac Ca2+ = orange-red Cu2+ = blue-green
What can photometry do better than simple flame tests?
- Better sensitivity (detect much smaller amounts)
- Accuracy (give values closer to true values)
- Speed (gives results faster)
What does a flame photometer measure?
Light intensity of the flame colours produced by metal ions
What does flame photometry produce?
A calibration curve produced using different standard solutions, each containing known concentrations of the metal ion dissolved in distilled water
What does a spectrum produced by a flame photometer show?
Since the colours produced are usually a mixture, the spectrum separates them out to detect which metal ion is is in the solution as different metal ions produce different emission spectra
How is a hydroxide precipitate produced?
- Sample solution placed in test tube
- Few drops of dilute sodium hydroxide solution are added
What hydroxide precipitates are produced by copper, iron (II) and iron (III)?
Cu2+ = blue Fe2+ = green Fe3+ = brown
How is a precipiate formed since sodium hydroxide is soluble in water?
Most hydroxides are insoluble and so form precipitates in these tests
How do you treat water that flows through mines and contaminates rivers?
React the metals with sodium hydroxide which will produce a precipitate which will settle out and can be removed
What colour precipitate does aluminium and calcium produce?
White
How can you distinguish between aluminium and calcium?
Do a further test - aluminium hydroxide disappears to form a colourless solution when excess sodium hydroxide is added, but calcium hydroxide does not
How do you test for ammonium ions?
- Add dilute sodium hydroxide solution to ammonium ions solution
- Ammonia gas is produced when ammonium ions mixture is warmed
- Ammonia has characteristic sharp smell but confirmatory test is used to identify it
What is the confirmatory test for ammonia?
Damp red litmus paper changes to blue when ammonia is present
Describe the test to identify metal ions in a solution using dilute sodium hydroxidde solution
- Using a dropping pipette, fill a test tube to depth of 2cm with solution
- Using different dropping pipette, add few drops of dilute sodium hydroxide solution to the tube
- Gently shake tube
- Observe and record colour
- If white do further test to distinguish between aluminium hydroxide and calcium hydroxide
How do you test for carbonate ions?
- Add dilute hydrochloric acid to the test substance
- Look for effervescence of CO2
- Carry out CO2 confirmatory test (bubble gas through limewater and should turn milky)
Why should you use dilute hydrochloric acid as opposed to concentrated?
- Less expensive
- Less damaging to the environment
How do you test for sulfate ions?
- Add few drops of dilute hydrochloric acid which acidifies the solution and removes carbonate ions that might give a precipitate in the test
- Add a few drops of barium chloride solution
- White precipitate of barium sulfate forms if the sample contains sulfate ions
Where do halide ions come from?
Group 7 halogens form compounds containing halide ions
Which silver halide is soluble unlike all others while are insoluble?
Silver fluoride
How do you test for halide ions?
- Add a few drops of dilute nitric acid which acidifies the solution and removes carbonate ions that might also give a precipitate in the test
- Add a few drops of silver nitrate solution
- Observe and record the colour
What are the colours for the precipitates formed in these halide ions?…
- Chloride
- Bromide
- Iodide
Cl- = white Br- = cream I- = yellow
What is a composite material?
A mixture of two or more materials combined together, each with different properties
What is the difference between a reinforcement material and matrix material in a composite material?
- Reinforcement = discontinuous phase
- Matrix - continuous phase
What is tensile strength?
Resistance to being stretched
What is compressive strength?
Resistance to being squashed
What is a laminate?
A material that is stronger along its grain than across its grain
What are ceramics?
Materials that are a range of durable compounds that change very little when heated
Describe common properties of ceramics
- Unreactive
- Hard
- Stiff
- Brittle
- Poor electrical and thermal conductors
- High melting points
- Giant structures with many strong covalent/ionic bonds
How are clay ceramics like brick, porcelain, and china made?
- Clay is moulded into desired shape
- Heated to very high temperatures and crystals form and join together
- Bricks usually decorated by adding coloured substance to clay before heating
- Porcelain and china dipped in ‘glaze’ and heated strongly again, forming hard, waterproof, smooth surface you see on tiles, washbasins and toilet bowls
How is glass made?
Melting sand, then allowing it to cool and solidify
How is glass and clay ceramics different?
Atoms in glass are not arranged in a regular way to form crystals, so glass is transparent rather than opaque
Describe how modern window glass is made by the float process
- Molten glass is poured onto a bath of molten tin, where it spreads out on the surface
- Flat layer of glass is drawn away and cooled in a continuous process
Describe some properties of polymers
- Very high relative formula masses
- Strong
- Chemically unreactive
- Poor electrical and thermal conductors
Give some uses for these materials…
- Glass ceramics
- Clay ceramics
- Polymers
- Metals
Glass ceramics = window glass, bottles
Clay ceramics - bricks, china, porcelain
Polymers = bottles, crates, carrier bags
Metals = cars, bridges, electrical cables
What is the difference between transparent, translucent and opaque?
Transparent = clear and fully see-through Translucent = lets light through but not detailed shapes Opaque = does not let light through
Why are lumps and powders examples of bulk materials?
They contain a huge number of atoms
How small are nanoparticles?
1-100nm
Are atoms or nanoparticles larger?
Nanoparticles, but they are smaller than cells
What are nanoparticulate materials?
They are substances that consist of nanoparticles; they occur naturally, but modern applications involve manufacturing them
What do the uses of nanoparticulate materials depend on?
- The small size of the nanoparticles
- Their large surface area to volume ratios
Describe the use of titanium dioxide, a nanoparticulate material
- In bulk it is a white solid
- Absorbs harmful UV radiation from sun which could cause skin cancer
- It is transparent because its particles are very small
- Almost-invisible sunscreen
What does the very large SA:V ratio mean for nanoparticles?
Makes them useful as catalysts
How do stain-resistant clothes treated with nanoparticulate materials stay clean?
The nanoparticles catalyse the breakdown of dirt
Why do some scientists think nanoparticulate materials pose a hazard to humans and the environment?
- Small size means can be breathed in or pass through cell-surface membranes
- Large SA:V ratios may allow them to catalyse harmful reactions or carry toxic substances bound to their surfaces
