Chemistry IGCSE Paper 3 Revision
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Describe the particles and their motion in the three states of matter.
- Solid- Particles vibrate in fixed postions
- Liquid- Particles can move across each other but not able to break free from the surface
- Gas- Particles far apart and free to move quickly
What is difusion?
- The movement of particles from an area of high conc. to an area of low conc. as the fast moving particles bump into each other and push each other away from the sourse
- Accelerated by heat
- Particles of lower molecular mass will difuse faster
- eg. spilled perfume will be smelt around the room after a few minutes
Describe paper chromatography.
- Place solute on paper on base line drawn in pencil.
- Place paper in solvent with solvent level below base line.
- Compare the components of the solution tested with known substances and their respective chromatographs.
- Chromatography works by testing the solubilty of the different subtances that make up the solution, thus by comparing the distances (which relate to the solubility of the substance) they travel up the paper with the known substances we can know.
If substances are colourless locating agents that mark them may be used to facilitate testing.
What are the most common methods for purification? Briefly describe each.
- Filtration - filter the solution to remove insoluble impurities. Resultant solution is called filtrate.
- Crystallisation - to obtain pure crystals from a solution, evaporate half the solution and allow it to cool. As this happens crystals will form. Filter resultant mixture, rinse with cold distilled water and dry the residue, which will be your final crystals, completely pure.
- Distillation - obtaining a pure liquid from an impure solution.
- Fractional distillation - separation of two liquids in a solution with different boiling points. Further detail in hydrocarbon section for separation of hydrcarbons.
State the relative charges and masses of:
- PARTICLE| MASS | CHARGE
- Electron, 0 (zero), -ve
- Proton, 1, +ve
- Neutron, 1, none
Define atomic number, mass number and isotope.
- Atomic Number - the number of protons, the defining factor of an element.
- Mass Number - the number of protons and neutrons in the nucleus.
- Isotope - an atom that has the same the same number of protons but a different number of neutrons, thus being the same element but with a different mass.
Define radioactivity, state the uses of radioactive isotopes.
- Instability of the nucleus causing the element to decay by emitting radiation.
- Uses include medical diagnosis, radiation treatment, sterilasation of medical equipment, measuring the thickness of sheets (paper, metal sheets, etc.), checking for cracks or imperfections in industrial machinery, and nuclear fuel.
Describe trends of melting points and reactivity in alkali metals and halides.
- Alkali Metals - As you go down the periods the elements become more reactive and have lower melting and boiling points.
- Halides - As you go down the periods the elements become less reactive and have higher melting and boiling points.
Describe ionic bonding.
- -Bonds between metal and non-metal.
- -Metal donate excess electrons and become positive ions.
- -Non-metals recieve electrons to become negative ions.
- -Ions are attracted because of opposing charges, and often are macromolecules in a giant, crystal, geometric structure.
- -High melting and boiling points, conduct electricity when in solution or molten.
Describe covalent bonding.
- -Between two non-metals.
- -Electrons are shared to complete outer ring, but are not transferred and no ions are formed.
- -Usually small structures, with low melting and boiling points and no electrical conductivity due to lack of free-flowing electrons.
- -An exception to this are the macromolecules that carbon forms, such as diamond, and that silicon dioxide forms.
- -Another exception is graphite, which DOES conduct electricity because of free electrons flowing through the layers.
Describe metallic bonds.
- -Positive ions form with a sea of electrons between them.
- -They form giant structures with a regular pattern, with atoms touching, but vibrating in place.
- -Conduct electricity and heat very well because electrons are free to move through material and transfer the energy.
- -Malleable and ductile, because rigid bonds do not hold the atoms in place and thus are free to move when enough force is applied, without breaking the bonds.
-Alloys are a mixture of two are more metals that are mixed to change the properties of the metal.
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