Chem - Practicals.doc
- 1. Separating insoluble impurities from a soluble substance (Removing sand and impurities from salt solution) Separating a mixture of immiscible liquids (Separating a mixture of water and hexane) Water and hexane are immiscible forming 2 separate layers and are separated using a separating funnel Separating a solvent from solution Simple distillation Separating a liquid from a mixture of miscible liquids Fractional distillation Separates mixtures of miscible liquids with different Bt’s, using a fractionating column increasing efficiency of redistillation process, packed with inert material(glass beads) increasing surface area where vapour may condense. - When mixture is boiled vapours of most volatile component(lowest Bt) rises into the vertical column where they condense to liquids. - As they descend they are reheated to Bt by the hotter rising vapours of the next component. - Boiling condensing process occurs repeatedly inside the column so there is a temperature gradient. - Vapours of the more volatile components reach the top of the column and enter the condenser for collection Boiling under reflux Where reagents volatile - condenses vapours and returns reagents to flask, prevents loss of reactants/products, prolonged heating for slow reactions - For preparation of aldehyde/carboxylic acid from alcohol (1)Reason for heating the mixture but then taking the flame away (1)provide Ea, exothermic/prevent reaction getting out of control Separating mixtures of similar compounds in solution (Separating dyes present in a sample of ink) Chromatogram Chromatography Different components of the dye spread out at different rates Using a square sheet of filter paper, spots of dye solutions are put along the baseline The filter paper is coiled into a cylinder and placed in a tank containing a small volume of solvent The lid is replaced on the tank, solvent rises up the filter paper When the solvent nearly reaches the top of the filter paper, the filter paper is removed and position of solvent marked. Dyes A & B are either pure substances or a mixture of dyes not separated with the solvent used
- 2. Dye C is composed of A & B as the spots correspond Colourless substances can be separated and seen by spraying/dipping the filter paper into a locating agent which colours the spots produced Separating a solid which sublimes, from a solid which doesn’t sublime Given a mixture of Ammonium chloride(sublimes) and sodium chloride(doesn’t sublime) Heat the mixture. Ammonium chloride turns directly to vapour but the sodium chloride remains unchanged When the vapour is cooled solid ammonium chloride collects free from sodium chloride A pure substance has a definite Mt, presence of impurities causes the substance to melt over a range of temperatures Best method of separation of (1) Oil and water (2) Alcohol and water (3) Nitrogen from liquid air (1) Separating funnel(2) Fractional distillation (3) Fractional distillation Mixture Compound - Proportions of the different elements can be varied - Properties are those of the elements making it up - Elements can be separated by simple methods - No energy gained or lost when the mixture is made - Different elements have to be present in fixed proportions - Properties different from properties of elements making it up - Difficult to separate into the elements which make it up - Energy usually given out/taken in when compound is formed Sub-atomic particles Protons, neutrons and electrons which makes up the atom Particle An atom, molecule, ion, electron or any identifiable particle RTP Room temperature and pressure Electron A negatively charged particle, with negligible mass occupying the outer regions of all atoms Immiscible Unable to mix, dissolve in each other, to form a homogenous mixture Miscible Soluble in each other (aq) Substance dissolved in water to form an aqueous solution State symbols Physical state of the reactants at RT Aqueous(aq) Solvent Substance in which other substances are dissolved Solute Substance dissolved in another substance(solvent)to form a solution Chemical species Collection of particles Distilled water Water that has been purified by distillation Ion When number of protons and electrons are different Atom The smallest part of an element that can exist on its own Molecule 2 or more atoms bonded together Element A pure substance which can’t be split up by chemical reaction Compound Combination of elements in fixed proportions via synthesis In formation of a compound from ions the charges balance out Physical properties: Mt, Bt, hardness • Compounds ending in –ate –ite contain oxygen, greater proportion of oxygen in the compound ending in –ate Sodium sulphate Na2SO4 Sodium sulphite Na2SO3 • Compounds with prefix per– contain extra oxygen Sodium oxide Na2O Sodium peroxide Na2O2 • Compounds with prefix thio– contain a sulphur atom in place of an oxygen atom Sodium sulphate Na2SO4 Sodium thiosulphate Na2S2O3 Metalloid Element which has properties between metals and nonmetals - Ions in an ionic compound are tightly held together in a regular lattice, lattice energy is required to break it up and melt the substance A metal high in the reactivity series has stable ores and the metal can be obtained only by electrolysis A metal middle in the reactivity series doesn’t form stable ores and can be extracted by reduction reactions (often with carbon) A metal low in the reactivity series, if present in unstable ores can be extracted by heating Decomposition Splitting up of a compound (Thermal decomposition - decomposition of a compound by heating) Combustion is the reaction of a substance with oxygen, total mass of products is greater than the mass of the substance burned, difference being the mass of oxygen combined Sublimation of an element/compound is a transition from solid to gas with no intermediate stage When a change of state takes place the temperature remains constant despite a continuing supply of energy. Latent heat is the energy which is not being used to raise the temperature and supplies particles with the extra energy they require as the state changes(given out when the reverse changes take place) Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s) Blue solution turns colourless and brown copper is deposited A displacement reaction where a more reactive metal replaces a less reactive metal in a compound Electrolysis of HCl(aq): 2HCl(aq) Cl2(g) + H2(g) Cathode: 2H+ (aq) + 2e– H2(g) Anode: 2Cl – (aq)Cl2(g)+2e– Heat Ammonium chloride NH4Cl(s) NH3(g) + HCl(g)
- 3. Cool A stopper from a bottle of (conc)NH3(aq) held near a stopper from a bottle of (conc)HCl acid gives a dense white smoke of NH4Cl