Chem

• Experimental techniques for the separation of mixtures

  1. Filtration

  2. Crystallisation

  3. Simple Distillation

  4. Fractional Distillation

  5. Paper Chromatography
• Chromatography


  1. Draw a pencil line near to bottom of the chromatography paper + add the spots of inks

  2. Add the solvent (water) in a beaker and add the paper

  3. The pencil line and the spots must Be ABOVE the solvent level

  4. Remove the paper when the solvent reaches the top of the paper/ solvent front
• Atomic Symbol


  The chemical symbol for an element
• Atomic Number


  The number of protons which is equal to the number of electrons in a neutral atom
• Atomic Mass


  The total number of protons and neutrons
• To find the number of neutrons in an atom you need to subtract the atomic number from the atomic mass
• Relative Atomic Mass (RAM/ Ar)


  The weighted average mass of the isotopes of an element, relative to the mass of the 1/12th of a 12C atom
• Isotopes


  Atoms of the same element, with the same number of protons but different number of neutrons
• Properties of Metals


  • Solids, high m.p, b.p, densities (EXCEPT Hg)
  • Metallic shine
  • Ductile
  • Malleable
  • Good conductors of electricity
  • Good conductors of heat
  • Sonorous
  • Form Cations (lose of e-)
  • Have basic oxides
  • Ionic bonds ( transfer of e-)
• Properties of Non-Metals


  • Gas, liquids, solids with low m.p & b.p, density (EXCEPT: C , Si)
  • Not shiny
  • Brittle
  • Don't conduct electricity (EXCEPT: C- in graphite form, Si)
  • Poor conductors of heat
  • Non-Sonorous
  • Form Anions (gain of e-)
  • Have acidic or neutral oxides
  • Ionic + Covalent bonds (sharing of e-)
• Noble Gases


  Unreactive / inert because they have Full outer shell, so they don't need to lose or gain e-
• Reaction with Water (Group 1 Alkali Metals)


  1. Floats, because is less dense than water

  2. Fizzing, because of hydrogen being produced

  3. Moves around rapidly, because of H2 given off not symmetrically around the piece of metal (ball)

  4. Gets smaller + Disappears, because is used up during reaction

  5. White trail formed, because of metal hydroxide that is formed

  6. Changes the colour of indicator, because of metal hydroxide that is produced (OH⁻)
• Differences in Reaction with Water (Group 1 Alkali Metals)


  • Li doesn't melt and slower reaction
  • Na + K melts into a ball, because of low mp and heat being produced (exothermic reaction)
  • K, faster, more vigorous reaction, K spitting around + igniting, burns with a lilac flame (because of K+)
  • Rb + Cs, react even more violently, explosive
• Group 1: Alkali Metals


  • Going down the group, Nuclei of the positive ions are further from the delocalised e-, so weaker electrostatic forces of attraction (metallic bond), so less E is needed
  • Bigger atoms, more p+, n◦, so heavier , so denser
  • Further down the group, the easier the outershell e- is getting lost, because more shells, so e- is further away from the nucleus, so less attracted
• Group 7: Halogens


  • F2 (gas, yellow, dangerously reactive)
  • Cl2 (gas, green, very reactive)
  • Br2 (liquid, red-brown liquid, dark orange vapour, very corrosive)
  • I2 (solid, dark grey solid, purple vapour, all have extremely poisonous vapours)
• Trends in Group 7: Halogens


  • Greater molar mass (more e-), stronger intermolecular forces, more energy required to break the forces (m.p)
  • Bigger atoms, greater molar mass (more p+, n◦) so heavier , so denser (b.p, density)
  • Going up the group, smaller atoms, nucleus closer to outer shell, so stronger force to the outer e-, extra e-more strongly attracted (reactivity)
• Displacement reactions involving Halogens


  1. KBr + Cl2 → KCl + Br2

  2. KI + Cl2 → KCl + I2

  3. KI + Br2 → KBr + I2

  4. KCl + Br2 → KBr + Cl2

  5. KBr + I2 → KI + Br2

  6. KCl + I2 → KI + Cl2
• Approximate percentages by volume of the four most abundant gases in dry air
• Reactivity Series of Metals

  • potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold
• Methods to prevent the rusting of iron

  • Barrier methods
  • Galvanising
  • Sacrificial protection
• Indicators


  Substances whose solutions change colour due to changes in pH, showing if a solution is acidic, alkaline or neutral
• Indicator Colour Changes


  • Methyl Orange (Acid: Red, Neutral: Orange, Base: Yellow)
  • Phenolphthalein (Acid: Colourless, Neutral: Colourless, Base: Pink / Red)
  • Litmus (Acid: Red, Neutral: Purple, Base: Blue)
  • Universal Indicator (Acid: Red, Neutral: Green, Base: Blue)
• Reactions of Acids


  • Acid + Metal → Salt + H2 ↑
  • Acid + Metal Oxide → Salt + H2O
  • Acid + Metal Hydroxide → Salt + H2O
  • Acid +Metal Carbonate → Salt + CO2↑ +H2O
• Bronsted-Lowry Theory


  • Acid → H+ - Proton Donor
  • Base → H+ - Proton Acceptor
• Making Soluble Salts (use of EXCESS solid)

  1. Warm the acid

  2. React with excess solid and Stir

  3. Filter the unused solid

  4. Heat the leftover solution (salt solution) to concentrate it, so most of the water will evaporate

  5. Test by cooling a drop of the solution using a stirring rod

  6. Let it to cool so crystals can form

  7. Filter of any excess liquid

  8. Let it dry in a warm oven or blot dry the crystals
• Flame Test Results


  • Li+ (Red)
  • K+ (Lilac)
  • Ca2+ (Orange - Red)
  • Na+ (Yellow)
  • Cu2+ (Blue-Green)
• Precipitation Reaction using NaOH

  For: Cu2+, Fe2+, Fe3+, NH4+
• Test for Positive Ions
• Organic General Formulas


  • Cn H2n+2 (Alkanes)
  • Cn H2n (Alkenes & Cycloalkanes)
• Isomers


  Molecules with same Molecular Formula, different Structural Formula
• Hydrocarbon


  Organic molecule with Carbon and Hydrogen ONLY
• Saturated


  Organic molecule with Carbon – Carbon single bonds
• Unsaturated


  Organic molecule with at least one Carbon = Carbon double bond
• Empirical Formula


  The simplest whole number ratio of atoms that make a compound
• Characteristics of a Homologous Series

  • Same General Formula
  • Same Functional Group
  • Similar Chemical Properties
  • Trends in the Physical Properties
  • Each member differs from the next by a –CH2-
• Fractional Distillation of Crude Oil

  1. Crude oil heated/vaporised and vapours rise up the column

  2. Column is cooler at top and hotter at bottom

  3. Fractions condense at different heights/levels

  4. As components / hydrocarbons / compounds / gases fractions have different boiling points
• Cracking


  Break down long hydrocarbon chains into smaller ones
• Importance of Cracking


  • Produces shorter Alkanes which are in greater demand
  • Produces alkenes which are very useful making polymers
• Conditions for Cracking


  1. Catalyst: Silica or Alumina

  2. Temperature: 600-700 ⁰C
• Cracking Reaction


  e.g. C13H28 → 2C2H4 + C9H20