Chemistry - Experimental Techniques

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  • Chemistry: Experimental Techniques
    • Equipment
      • pestle and mortar
      • tripod
      • gauze mat
      • Bunsen burner
      • Pasteur pipette
      • filter paper
      • weighing boat
      • heatproof mat
      • evaporating dish
      • watch glass
      • balance
      • measuring cylinder
      • conical flask
      • measuring beaker
      • test tube holder
      • funnel
      • thermometer
      • timer
      • burette
      • pipette
      • volumetric flask
    • Methods of Seperation
      • Filtration
        • used to separate a mixture of an insoluble solid from a liquid
        • equipment needed: filter paper, funnel, conical flask
        • the liquid particles are small enough to pass through the filter paper (as 'filtrate'). the solid particles are left behind as the 'residue'
      • Distillation
        • used to separate miscible liquids (eg. water and alcohol)
        • equipment needed: distillation apparatus, including a condenser
        • the liquid with the lower boiling point boils first. the gas passes into the condenser, here it cools down and reforms the liquid. there it will pause in boiling when all this liquid has passed over as 'distillate'. when the next boiling point is reached, the second liquid comes over
      • Crystallisation
        • used to get a solid from a saturated solution
        • equipment needed: evaporating dish, heating apparatus, saturated solution
        • the liquid evaporates to leave behind crystals of solid
      • Chromotography
        • used to separate and purify coloured compounds
        • equipment used: filter/ chromatography paper, a solvent, pencil/rod, beaker
        • the colours separate up the paper if the pigments have different solubilities in the solvent and/or the pigments have different degrees of attraction for the filter paper
    • Chromatography
      • can be used to identify colourless substances
        • same way as normal chromatography but a mark is drawn near the top of the paper to show where the solvent has reached
          • solvent front
          • chromatography paper is then dried and sprayed with s chemical called a locating agent
            • the locating agent then reacts with the chemicals in the colourless spot and a coloured compound is formed
              • the colour is usually developed by warming the paper in an oven
      • can identify the substances on the chromatogram by comparing how far the spots have moved from the base line compared with the solvent front
        • Rf value
          • Rf value = distance from base line to the center of the spot ÷ distance of solvent front from the base line
      • chromatography can be used to separate a mixture of dyes. the solubility of the dyes in the solvent determines how far they travel up the filter paper
        • can be used to identify compounds
    • Summary
      • apparatus for measuring
        • in chemistry, mass is measured in grams, temperature in °C and volume in cm^3 or dm^3
        • the apparatus you select for an experiment depends on the accuracy required in your experiment
        • volumes of gases can be measured using a gas syringe or by displacement of water
      • paper chromotography
        • chromatography is a method of separating and purifying coloured compounds using filter paper and a solvent
        • chromatography can be used to identify compunds
        • locating agents are used to make colourless compounds visible on a chromatogram
        • the compounds on a chromatogram can be identified using their Rf values
      • is that chemical pure?
        • melting and boiling points can be used to identify pure substances
        • a pure substance melts and boils at a definite temperature. an impure substance melts and boils over a range of temperatures
      • methods of purification
        • solids can be separated from solutions by filtration, decanting or centrifugation
        • crystals are formed when a solution of a crystalline solid is partly evaporated then allowed to cool
        • solvent extraction can be used to separate two solids dissolved in a liquid
      • more about purification
        • simple distillation is used to separate water from a dissolved salt
        • fractional distillation is used to separate more volatile liquids from less volatile liquids
        • purification of a mixture often involves a combination of methods

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