C4 - Predicting and Identifying Reactions and Products

Group 1 - alkali metals
1. One outer shell electron
2. Similar physical properties
  1. Low melting/boiling points relatively
  2. Low density (Li, Na and K float in water)
  3. Very soft (can be cut with a knife)
3. Form ionic compunds
4. Very reactive
  1. readily lose their single outer shell electron
    1. Form a 1+ ion
  2. As you move down group 1, the metals become more reactive
    1. Outer electron more easily lost as it's further away form the nucleus so is less reactive
5. reacts with water
  1. Metal + water => metal hydroxide + hydrogen
    1. 2Na + 2H20 => 2NaOH + H2
  2. React vigorously in water
  3. As reactivity increases, the metals react differently
    1. Lithium moves around and fizzes furiously
    2. Sodium and potassium also fizz like lithium but they melt in the heat of the reaction
    3. Rubidium and Caesium react violently and tend to explode
6. Can also react with dilute acids
  1. produces a salt and hydrogen gas
    1. 2Na + 2HCl => 2NaCl + H2
  2. More violent than reacting with water so can be dangerous
Group 7 - halogens
1. 7 electrons in the outer shell
2. Exist as diatomic molecules
  1. Exist as Cl2 or Br2
  2. Covalently bonded
3. Melting/boiling points INCREASE as you go down the group
  1. Chlorine is a fairly reactive poisinous green gas
  2. poisonous red-brown liquid, gives off an orange vapour
  3. Iodine is a dark grey crystalline solid which gives of a purple vapour when heated
4. Reactivity decreases going down the group
  1. Only needs to gain one electron to form a 1- ion
  2. The easier it is to attract the electron, the more reactive the halogen will be
    1. it's harder to attract an electron as it's further away from the nucleus as the atomic radius grows
5. React with alkali metals to form salts
  1. Sodium + chlorine => sodium chloride
    1. 2Na + Cl2 => 2NaCl
  2. alkali metal + halide => metal halide
6. Halogens undergo displacement reactions
  1. a more reactive halogen can displace a less reactive one from a salt solution
  2. If you add chlorine water to potassium bromide solution, the chlorine will displace the bromine from the solution
    1. Cl2 + 2KBr => Br2 + 2KCl
  3. These show the reactivity trends of the halogens
    1. measure the halide salt solution into a testube
      1. add a few drops of the halide solution and gently mix
        a colour change indicates a reaction has happened
Group 0 - noble gases
1. All Group 0 elements are INERT
  1. They don't really react at all. They have a full outer shell of electrons meaning they don't easily give up or gain electrons
  2. They are not flammible
  3. These properties means it's difficult to observe them, they took a long while to be discovered
2. There are patterns in properties
  1. boiling/melting point and density increase as you move down the group
  2. You can estimate values of elements:
    1. He (0.2kg/m^3) and Ar (1.8kg/m^3) means Ne is in the middle so 0.1kg/m^3
Transition metals
1. "Everyday" metals, eg copper, iron, gold...
2. Have typical metallic properties
  1. Hard, strong, shiny materials that conduct heat and electricity very well
  2. HIgh melting points (apart from mercury)
3. Make good catalysts
  1. Iron is used in the Haber process (ammonia)
  2. Vanadium pentoxide (V2O5) is used in the contact process (H2SO4)
4. Can have multiple ions
  1. Fe2+ and Fe3+
  2. Cu+ and Cu2+
  3. Cr2+ and Cr3+
5. Colourful compounds
  1. the colour depends on the transition metal they contain
    1. Fe2+ is usually light green
    2. Fe3+ is usually orange/brown (rust)
    3. Cu2+ is usually blue
6. Transition metals are fairly unreactive
  1. Much less reactive than group 1 and 2 metals
  2. Most react with dilute acids to form metal salts but they happen much slower than g1 or g2 metals
Reactivity of metals
1. How metals react with acid can tell you about their reactivity
  1. place pieces of various metals in HCl. The more reactive, the faster the reaction will happen
  2. reactive metals will fizz vigorously, whereas less reactive metals might bubble a bit
    1. You can show that hydrogen is formed by using the burnt split test
2. Metals can react with water
  1. metal + water => metal hydroxide + hydrogen
3. A reactivity series shows how reactive metals are
  1. For example it will show that Potassium is more reactive than Magnesium
4. More reactive metals displace less reactive ones
  1. if you put an iron nail into a solution of copper sulfate, the more reactive iron displaces the copper
    1. CuSO4 + Fe => FeSO4 + Cu
  2. if you put a less reactive metal into a solution of a more reactive metal salt, nothing will happen
  3. You can use displacement reactions to work out a reactivity series
Test for gases
1. Oxygen
  1. The gas will relight a glowing splint
    1. This is because combustion only happens when oxygen is present so if the gas is not oxygen, the flames will smother
2. Testing for gases can be dangerous
  1. Some gases are pretty nasty
  2. Tests should be carried out in fume cupboards for safety
3. Carbon dioxode
  1. Limewater will turn cloudy if CO2 is bubbled through
4. Hydrogen
  1. Makes a "squeaky pop" with a lighted splint
    1. The noise comes from hydrogen burning with oxygen in the air to form oxygen
5. Chlorine
  1. Damp blue litmus paper will bleach and turn white
    1. The paper may turn red first as chlorine is acidic
Tests for anions
1. Sulfates
  1. Add barium chloride solution then a white barium sulate precipitate will form
    1. Ba2+ +SO42 => BaSO4
    2. The BaSO4 will not react with the HCl, so the white precipitate will not dissolve
2. Halide ions
  1. Add dilute nitric acid (HNO3) then some silver nitrate solution and precipitates should form
    1. Chloride gives a white precipitate AgCl
    2. Bromide gives a cream precipitate AgBr
    3. Iodide gives a yellow precipitate AgI
3. Carbonates
  1. Add barium chloride solution then a white barium carbonate precipitate will form
    1. Next add HCl and if carbonates are present, it will fizz producing CO2 gas
      1. BaCO + 2H+ => Ba2+ + CO2 + H2O
      2. You can test for Carbon dioxide with the limewater test
Tests for cations
1. The flame test can identify metal ions
  1. Lithium, Li+, crimson red
  2. Sodium, Na+, yellow
  3. Potassium, K+, Lilac
  4. Calcium, Ca2+, brick red
  5. Copper, Cu2+, blue-green
2. Some metal ions form a coloured precipitate with NaOH
  1. you add a few drops of sodium hydroxide solution to your compound. If a hydroxide precipitate forms, you can use the colour to figure out the ion.
    1. Calcium, Ca2+, white
      1. Ca2+ + 2OH- => Ca(OH)2
    2. Copper, Cu2+, Blue
      1. Cu2+ + 2OH- => Cu(OH)2
    3. Iron, Fe2+, Green
      1. Fe2+ + 2OH- => Fe(OH)2
    4. Iron, Fe3+, Brown
      1. Fe3+ + 3OH- => Fe(OH)3
    5. Zinc, Zn2+, white at first then dissolves in excess NaOH to a colourless solution
      1. Zn2+ + 2OH- => Zn(OH)2
        Zn(OH)2 + 2OH- => Zn(OH)4 2-

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C4 - Predicting and Identifying Reactions and Products

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	Created by Lucy Smith over 6 years ago