chemistry- topic 8 chemical analysis

What is a pure substance

Consists of only one element or one compound

What is an impure substance

A mixture of two or more elements and or compounds

What is a formulation?

• a mixture that have been designed as a useful producer

• E.g. lipstick

• Pencil

• Toothpaste

What is chromatography used for?

• separating coloured or non coloured substances that are soluble in the same solvent

What are substances separated based on in chromatography?

• how soluble they are in in the solvent used

• How strongly they are attracted to the paper

What are the two phased of chromatography?

• mobile phase - liquid solvent that moves through the stationary phase (e.g. water)

• Stationary phase - usually paper doesn’t move

What can paper chromatography be used for?

• to distinguish pure substances from impure substances

How can you tell the most soluble substance in chromatography?

• it is higher up the page

How do you calculate the R.f value for chromatography?

• distance moved by substance / distance moved by solvent

• Always less than 1

How can you differentiate between a pure and impure substance?

• they have different melting + boiling points

What is the test for hydrogen?

• squeaky pop when a light splint is held at end of test tube

What is the test for oxygen?

• glowing splint that re-lights when put back into test tube

What is the test for carbon dioxide?

• Lyme water which will turn cloudy if carbon dioxide is bubbled through it

What is the test for chlorine

• Damp litmus paper that will turn from blue to bleach white

What colour does copper turn in a flame test?

Green

What colour does calcium turn in a flame test?

Re/orange

What colour does lithium turn in a flame test?

crimson

What colour does sodium turn in a flame test?

Yellow

What colour does pottasium turn in a flame test?

lilac

Advantages of instrumental analysis (use a machine)

• very sensitive

• Very fast

• Very accurate

How does flame mission emmison spectroscopy work?

• a sample of solution contains metal ions is placed in flame

• As ions heat up they become excited when they return to original energy levels they transfer energy as light

• Light given out passed through a spectroscope, this detects wavelengths and produces a line spectrum

• Each ion produces a differently line spectrum

• The intensity of the spectrum indicates the concentration of the ion in solution

Flame emissions spectroscopy in mixtures

• can pick up different ions that would usually be masked in flame test

• Compare with known line spectrum to find out which ions are in solution

How to test for carbonates in ion solutions ?

• carbonate + acid form salt + co2 + water

• Bubble the carbonate through dilute HCL and then bubble gas produced through lime water

• If it turns cloudy then CO2 is present and so are carbonates

How do you test for sulphate ions ?

• barium ions + sulphate ions form a white precipitate

• Add dilute HCL to sulphate to remove the carbonates and sulphites

• Add barium chloride and if a white precipitate produces then the sulphate are present

How to test for halide ions?

• silver nitrate + halide results in precipitate

• Use chlorine , bromide iodine

• Add dilute nitric acid to remove carbonates and sulphites

• Add silver nitrate

What precipices are produced by the halide ions ?

• chloride = white

• Bromide = cream

• Iodide = yellow

What are the test for cations (white precipitate?)

• add sodium hydroxide

• Magnesium, calcium and aluminium ions all produce white precipitate

• Add excess sodium hydroxide to redisolve the aluminium and it turns colourless

What colour precipitates are produced from iron III, copper II and iron II?

• iron III =brown

• Copper II = blue

• Iron II = green

• All with sodium hydroxide