Contents
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Kinetic Particle Theory
Solids, Liquids and Gases.
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What is diffusion? |
[Diffusion is the movement of particles from a highly concentrated region to a lower-concentrated region of particles.]
- The greater the mass of the molecules, the slower the rate of diffusion.
- The higher the temperature, the faster the particle will move and hence the faster the rate of diffusion.
Melting
[The temperature that at the solid melts is called the melting point.]
[Solid -> Liquid]
-When a solid is heated:
Its particles gain energy and vibrate more vigorously until they overcome the forces holding them in their fixed positions and start to slide around other particles in the liquid.
-Pure substance has a fixed melting point.
Freezing
[Liquid- Solid]
-Process of Freezing.
As the liquid is cooled, its temperature decreases until its freezing point is reached.
Heat energy is released as the particles slow down and takes up fixed and orderly positions in the solid.
-The temperature stays constant during melting, freezing.
Melting:
The heat energy is absorbed by the solid, to separate the particles further apart, from a fixed and orderly to a random arrangement.
The heat energy is absorbed NOT to make the particles move faster.
Freezing:
The amount of energy released is equal to the amount of energy lost to cooling, hence the temperature is constant.
-Impurities lower the melting point and increase the boiling point
Boiling
-The particles gain energy and move more quickly until they completely break the forces holding them together and the particles become far apart and able to move freely in high speed.
-Pure substance has a fixed boiling point only at a fixed pressure.
-As pressure increases, the boiling point increases.
Evaporation
-Particles of higher kinetic energy escape to the surface of the liquid to form a gas.
-Occurs below boiling point of liquid.
-Takes place at surface of liquid.
-Very slow
Condensation.
[Gas -> Liquid]
-The gas is cooled and changes to liquid
-Change from gaseous state to solid state without going through liquid state is possible in condensation.
Sublimation
-Change of solid to gas without melting.
E.g. Ammonium Chloride, Solid Carbon Dioxide ( Dry Ice), Iodine.
Purification Techniques.
Purity can be tested by melting/boiling points or by chromatography.
| | Pure Substances | Mixtures |
| Composition | A single substance. | Contains two or more substances. |
| Melting and Boiling points | Fixed points | Over a range of temperatures. |
Again, impurities in a pure substance will lower its melting point and raise its boiling points.
Filtration
-Separate insoluble solid from liquid
-Residue - collected in the filter paper.
-Filtrate – Passes through the filter paper.
Crystallisation
-Separate dissolved solid from a solution as crystals.
-Used to obtain pure sugar or silicon chips used in computers.
Steps:
-Dissolve the impure solid in a solvent.
-Solution is heated to evaporate most of the solvent until a saturated solution is obtained.
-On cooling, crystals are formed.
-Fast cooling : Small crystals. Slow cooling : Large crystals.
Sublimation
-Separates a mixture of solids, one of which sublimes.
-E.g. Iodine, solid carbon dioxide ( Dry Ice), anhydrous iron(III) chloride,…
Separating Funnel
-Separate *immiscible liquids.
*Immiscible liquids – Liquids which do not mix with each other, e.g. water and oil.
Simple Distillation
-Separate pure liquid (solvent) from a solution (of a solute).
-Distillate – Vapour which condenses to become the pure liquid.
Steps:
-Solution is heated in flask until solution boils.
-Pure liquid turns in vapour and leaves the flask.
-Vapour is cooled by condenser, which turns it back in a liquid.
-Liquid (Distillate) is collected in a conical flask.
Fractional Distillation
-Separate a mixture of miscible liquids with widely differing boiling points
Steps:
-Solution is heated in flask until it boils.
-Liquid with lowest boiling point comes out of fractionating column first.
-Vapour is cooled by condenser, which turns it back to a liquid.
-Liquid is collected in a conical flask.
-Liquid with higher boiling point remains in flask.
-Fractionating is packed with glass beads to give a large surface area so that vaporization followed by condensation takes place many times.
This is to ensure that only the liquid with the lowest boiling point enters the condenser.
Eventually, the liquid with the lower boiling point reaches the top of the column first and distills over.
-Thermometer measures the temperature of the vapour so that the vapour being condensed can be identified.
-Used to separate pure oxygen and pure nitrogen from liquid air, produce alcoholic drinks,..
Chromatography
-Separate tiny quantities of mixtures for identification purposes, e.g. dyes used in food.
-Works on the fact that different substances have different solubilites in a type of solvent.
-The more soluble solution travels a longer distance.
-Locating agent used to identify colourless spots by reacting with the substances on the paper to produce a coloured product.
E.g. Sliver nitrate solution, concentrated sulfuric acid.
-Starting line is drawn using pencil as lead is insoluble and would not dissolve in the solvent and interfere with the chromatogram making the results inaccurate, unlike ink.
Descending chromatography VS Ascending chromatography
-Solute is not traveling against gravity.
-Solutes can travel further, thus the separation between each spot is greater.
Rf values = distance moved by substance/distance moved by solvent.
-Depends on temperature and solvent.
Atomic Structure
| Particle | Relative Mass | Relative electric charge. |
| Proton | 1 | 1+ |
| Neutron | 1 | 0 |
| Electron | 1___ 1836 | 1- |
Nucleus : Protons and Electrons
Shells : Electrons
Mass of Electrons is negligible
Nucleon number : Protons + Neutrons
Atomic number : Protons
Isotopes : Different atoms of the same element with different numbers of neutrons but same number of protons and electrons.
-Have similar chemical properties but different physical properties as they have different molecular mass.
Electronic Arrangement
Energy levels filled in order of increasing energy.
Shell closest to nucleus are more strongly attracted.
Same group = same valence electrons
Valence electrons = group number.
Noble gas have stable electronic structure, thus do not form atoms.
Metal lose electrons to form positive ions
Non-metal gain electrons to form negative ions
Positive ions = Cation
Negative ions = Anion
Atom = Neutral.
