Analysis Flashcards
What is an element?
- atoms with the same atomic number
What is a compound?
- two or more different elements chemically bonded together in fixed proportions as a result of a chemical reaction
What is a mixutre?
- contains 2 or more elements or compounds
- individual substances are not chemically combined
- individual components not in fixed proportions
What is a pure substance?
- one element or one compound only
What is the difference between melting and boiling points between pure and impure substances?
- pure - specific melting/ boiling point
- impure - range of temperatures
What is a formulation?
- mixture that has been designed as a useful product
What is the difference between a formulation and a simple mixture?
- many components
- fixed proportion of each component
What are some examples of formulations?
- cleaning products
- fertilisers
- fuels
- medicines
- foods
How are formulations made?
- mixing components in controlled quantities
- each individual substance has particular purpose
- so that formulation has desired properties
What does chromatography do?
- separate a mixture of coloured solutes in a solution
- used to identify substances
- involves a stationary phase and a mobile phase
What is a stationary phase?
- does not move
- paper in case of chromatography
What is a mobile phase?
- moves through stationary phase
- solvent in case of chromatography
water or ethanol could be the solvent
What affects the Rf value of a substance?
- relative strengths of bonds to the mobile or stationary phase
- stronger bond to mobile phase = longer distance up the paper
- stronger bond to stationary phase = shorter distance
How do you calculate the Rf value of a substance?
Rf = distance moved by substance/ distance moved by solvent
How do you conduct a chromatography?
1) draw baseline with pencil (won’t dissolve)
2) add spot of sample to baseline
3) fill beaker with shallow solvent
4) place in solvent
5) remove and dry
How do you identify hydrogen
- hold lit splint near open test tube
- if “pop” is heard then hydrogen is present
How do you identify oxygen?
- hold glowing splint in test tube
- if relights then oxygen is present
How do you identify carbon dioxide?
- shake gas with limewater
- if limewater turns cloudy/ milky then CO2 is present
How do you identify chlorine?
- put damp litmus paper into gas
- if litmus paper turns white then chlorine is present
How do you clean the nichrome wire for a flame test?
1) dip loop in dilute hydrochloric acid
2) hold loop in hot part of blue bunsen burner flame
3) repeat 1&2 until there is no extra colour to flame
How do you conduct a flame test on a solid sample?
using a damp wooden splint
How do you test a sample in the flame test?
1) dip loop in dilute hydrochloric acid then sample
2) hold loop on edge of blue bunsen flame
3) observe + record colour of flame
What colour is the flame when the Li+ cation is present?
Crimson
What colour is the flame when the Na+ cation is present?
yellow
What colour is the flame when the K+ cation is present?
purple
What colour is the flame when the Ca2+ cation is present?
orange- red
What colour is the flame when the Cu2+ cation is present?
green
What compounds are soluble in water?
most potassim, sodium or lithium compounds
What happens when insoluble compounds are produced?
- appear as jelly-like/ cloudy precipitates
How do you conduct a precipitate test?
1) use clean pipette to transfer 1-2cm^3 of test solution to test tube
2) use another pipette, add few drops of sodium hydroxide solution
3) observe colour of any precipitate
4) if white precipitate forms -> add more sodium hydroxide to see if it dissolves
What colour precipitate is produced by the Fe2+ cation?
green
What colour precipitate is produced by the Fe 3+ cation?
brown
What colour precipitate is produced by the Mg2+ cation?
white
What colour precipitate is produced by the Ca+ cation?
white
What colour precipitate is produced by the Cu 2+ cation?
blue
What colour precipitate is produced by the Al 3+ cation?
white- dissolves in excess sodium hydroxide
What is a cation?
a positively charged ion
What is an anion?
a negatively charged ion
How do you test for carbonate ions?
1) add few drops of dilute hydrochloric acid to solid sample/ solution
2) if carbonate ions are present = bubbles of gas are given off
3) gas may not be carbon dioxide -> limewater test
How do you test for halide ions?
1) Add a few drops of dilute nitric acid to sample
2) add a few drops of silver nitrate solution
3) observe colour of precipitate formed
What colour precipitate is formed with a Cl- ion?
white
What colour precipitate is formed with a Br- ion?
cream
What colour precipitate is formed with a I- ion?
yellow
What are the advantages of instrumental methods of analysis?
- faster
- sensitive (can detect very small quantities of a substance)
- accurate (correctly detect & identify substances in sample)
What are the disadvantages of flame tests?
- can only detect prescence of metal ions
- cannot measure concentration
- uncertain if sample is mixture of metal ions
How does flame emission spectroscopy work?
- sample heated in flame
- thermal energy provided excites electrons in ion -> jump to higher energy levels
- fall back to lower shells -> emit energy in form of light
- light emitted passed through spectroscope, intensity + wavelengths used to identify metal ions
- combination of wavelengths depends of charge of ion + electronic config
- output = emission spectrum, different ions produce lines in different parts of spectrum
- line spectrum compared against computer database to identify ion
How do you test for sulfate ions?
- add hydrochloric acid to sample
- add barium chlroide
- white precipitate of barium sulfate prodcuted if sulfate ion present
