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2014-03-28 06:13:52
chemistry,first term
Chemistry - First term
Show Answers:

  1. What is an atom?
    • type of particle
    • cannot be broken down chemically
    • no nett charge
    • forms elements
  2. What is a molecule?
    • type of particle
    • 2 or more atoms
    • usually non metals
  3. What is an ion?
    • type of particle
    • has an electric charge
    • either single or in a group
  4. What are the three states of matter?
    • Solid
    • Liquid
    • Gas
  5. Describe the characteristics of a solid.
    • -has a definite shape / volume
    • -atoms close together

    • -Arrangement: fixed pattern
    • -Movement: particles vibrate in place
    • -Attractive forces: Strong
    • -Proximity: Close together
  6. Describe the characteristics of a liquid.
    • -has a definite volume 
    • -takes shape of container

    • -Arrangement: no fixed position
    • -Movement: particles flow/slide passed each other
    • -Attractive forces: Weak
    • -Proximity:  Further apart (still close)
  7. Describe the characteristics of a gas.
    -no definite volume/shape (unless in closed container)

    • -Arrangement: randomly arranged
    • -Movement: random movement, moves everywhere rapidly
    • -Attractive forces: Weakest
    • -Proximity: Far apart
  8. Why do solids have low movement?
    They have low energy and strong attractive forces.
  9. Why do gases have high movement?
    They have high energy and weak attractive forces.
  10. What are the changes of state?
    Melting, boiling/evaporation, condensing, freezing.
  11. Heating Curve
  12. What is sublimation?
    When a solid becomes a gas.
  13. What is deposition?
    When a gas becomes a solid.
  14. Name a few endothermic processes.
    Melting, boiling, evaporation, sublimation.
  15. Name a few exothermic processes.
    Freezing, condensing and deposition.
  16. Describe how a solid is heated.
    • solid is heated
    • particles gain energy and vibrate
    • forces of attraction weakens
    • solid melts

    (there's no temperature change at the melting point as energy is absorbed to overcome attractive forces)
  17. How does temperature and pressure affect gases?
    The higher the temperature, the higher the volume (particles move more rapidly)

    The higher the pressure, the lower the volume (compressed)
  18. Define diffusion.
    The random movement and collision of particles in a medium which causes the particles to spread / mix.
  19. What is the kinetic particle theory?
    The theory that particles are constantly moving.
  20. How does relative molecular mass affect diffusion?
    The higher the relative molecular mass, the heavier the molecule and the slower the rate of diffusion.
  21. What are the factors which affect diffusion?
    • Temperature: Higher the temperature, higher the rate of diffusion 
    • Mass: Higher the mass, lower the rate of diffusion
    • Size of particle: Higher the size, lower the rate of diffusion
  22. What is paper chromatography?
    A method for separating and purifying coloured compound based on solubility.
  23. When would paper chromatography work?
    When the pigments have different solubilities in the solvent

    When the pigments have different degrees of attraction for the filter paper
  24. What are the steps for a paper chromatography?
    • Base line is drawn in paper
    • Colour dye is transferred
    • Paper is dipped into solvent
    • Beaker is closed
    • Draw line at solvent front
    • Calculate retention values
  25. How do you calculate retention value?
    •  distance from base line to centre of spot
    •         distance of solvent front from base line
  26. What solvents could you use for paper chromatography?
    Water, ethanol, propanone
  27. What's the use of paper chromatography?
    • To identify substances in mixture
    • To separate out substances in a mixture (thereby purifying them)
  28. How do you conduct paper chromatography for a colourless substances?
    • Paper is dried and sprated with a locating agent (ninhydrin in amino acids - reacts with substance to form colour compound)
    • Paper is shone under UV light / warmed in oven
  29. What is chemical purity?
    When only one substance is present.
  30. What is the importance of purity?
    • Impurities in food additives / medical drugs have harmful effects on health
    • In computer chips (supposed to be pure silicon) the chips will not work properly
  31. How do you identify pure substances?
    Using their distinct / sharp melting and boiling points

    • The more imipurities, the wider the range of temperatures
    • Boiling point is increased by impurities
    • Melting point is decreased by impurities
  32. What is decanting?
    • Pouring off the solid from a solution.
  33. What is filtration?
    • Separating an undissolved solid (solute) from a solution (solvent) by passing it through filter paper

    Simple / Büchner filter

  34. What is centrifugation?
    A centrifuge spins the solution at a high speed. The denser substance will be collected at the bottom. (can then be followed by decanting)
  35. What are the steps for crystallization / evaporation?
    • 1) gently heat in evaporating dish to concentrate
    • 2) evaporate till crystallisation point
    • 3) leave to cool, filter
  36. What is a separation funnel?
    • A funnel which separates two immiscible solutions (liquids that don't mix)
    • Could also be used with two solutes dissolved in a single solvent (useless if volatile - evaporates easilly)
  37. What is distillation?
    • A method of separating a liquid from a mixture by boiling the mixture then condensing the vapours.
    • Simple: Mixture of solid and liquid (salt in water)
    • Fractional: Mixture of liquids at different boiling points (ethanol and water)
  38. What is an emulsion?
    Tiny droplets of oil suspended in water

    • (eg: oil and water mixed homogenously)
    • homogenously: in the same phase, hard to separate
    • heterogenous: different phases, easy to separate
  39. What is an emulsifier?
    Something which helps to mix liquids. 

    (eg: egg yolk in sald dressing)