8. Chemical Analysis Flashcards
What is a pure substance?
Made up of just one substance - either an element or a compound
How are properties changed when impurities are introduced?
- conductivity
- strength
- melting and boiling point
What happens when salt is added to pure water?
The salt dissolve to produce an impure substance (salt lowers the temperature of ice) so melts the ice
Difference between melting/boiling point between pure and impure substances?
Pure substances melt at a specific temperature whereas impure substances can melt or boil at a range of temperatures
How does melting point of an impure substance compare to that of a pure one?
Impure substances have lower melting points than pure substances
What is a formulation?
A mixture of compounds/substances that do not react with each other but produce a mixture to suit a particular use
Examples of formulations?
Toothpaste, moisturiser, make up, alloys, paint, medicines
What does pure mean in advertising?
Nothing else has been added to the product
What are some different types of food additives?
Preservatives, colourings, flavour enhancers
What is chromatography?
A technique for separating mixtures into their components in order to analyse, identify, purify the mixture or components
What is the mobile phase in chromatography?
The solvent (e.g. water)
What is the stationary phase in chromatography?
The paper
What is Rf factor?
Distance substances move up the paper in a certain amount of time
How to work out Rf factor?
Distance moved by substance / distance moved by solvent
What is the solvent front?
Point at which water stops moving up the paper
What is the centre spot?
Point at which a band or spot of colour is
What is the baseline?
Line where original sample was placed
How is chlorine tested for?
Electrolysis
How is carbon dioxide tested for?
Limewater turns cloudy
Hydrochloric acid + calcium carbonate
How is oxygen tested for?
Glowing splint relights
Hydrogen peroxide -> water + oxygen
How is hydrogen tested for?
Squeaky pop test
Mg + HCl -> MgCl + H2
Ways to test for positive ions?
Flame test and sodium hydroxide/precipitate test
What is the flame test?
Using the colour of the Bunsen flame to identify the metal ion in the compound
What does a crimson flame show?
Lithium present
What does a yellow flame show?
Sodium present
What does a lilac flame show?
Potassium present
What does a red flame show?
Calcium present
What do the flame colours show is present?
Crimson - lithium
Yellow - sodium
Lilac - potassium
Red - calcium
How to carry out the precipitate test?
Add 1cm3 of NaOH solution, if precipitate is white add an excess of NAOH solution
What do coloured precipitates show in the sodium hydroxide test?
Blue - copper
Green - iron (II)
Brown - iron (III)
What does a blue precipitate show in a test for positive ions?
Copper present
What does a green precipitate show in a test for positive ions?
Iron (II) present
What does a brown precipitate show in a test for positive ions?
Iron (III) present
What does a white precipitate show in a test for positive ions?
Either aluminium, calcium or magnesium
What does a soluble white precipitate show in a test for positive ions?
Aluminium present
What does an insoluble white precipitate show in a test for positive ions?
Either calcium or magnesium present
What is a halide?
A charged halogen
What are the tests for negative ions?
Halide test, carbonate test and sulphate test
What is the halide test?
Add dilute nitric acid and silver nitrate solution - if precipitate forms a halide is present
What does a yellow precipitate show in the halide test?
Iodide ions present
What does a cream precipitate show in the halide test?
Bromide ions present
What does a white precipitate show in the halide test?
Chloride ions present
What is the sulphate test?
Add dilute HCl then barium chloride soliton - white precipitate show sulphate ions present
What does a white precipitate show in the sulphate test?
Shows sulphate ions are present
What is the carbonate test?
Add dilute HCl - bubbles produced = use teat pipette to transfer gas produced to limewater - limewater milky means carbonate ions present
What does milky limewater mean in the carbonate test?
Carbonate ions are present
How can substances be analysed?
Using a methods including paper chromatography, gas chromatography, mass spectrometry and flame emission spectroscopy
How is flame emission spectroscopy carried out?
Sample is put into flame and then the light given off is passed through a spectroscope
What is the output in flame emission spectroscopy?
A line spectrum that can be analysed to identify metal ions and concentration
Advantages of flame emission spectroscopy?
- quick
- accurate
- sensitive - only requires a small sample
- brightness of spectrum = concentration
Disadvantages of flame emission spectroscopy?
- destructive- sample being tested is burned
* only identifies presence of elements not compounds
Application of flame emission spectroscopy?
- quality control in chemical manufacture
- working out composition of distant stars
- drug detection