Chemical changes

• Metals react with oxygen to produce metal oxides. The reactions are oxidation reactions because the metals gain oxygen.
• What happens when we cut a piece of lithium?

  We expose its surface which is very shiny but if very quickly goes dark because it reacts with the oxygen in the air to make Lithium Oxide
• State the reactivity series in order 


  potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen and copper
• The non-metals hydrogen and carbon are often included in the reactivity series.
• Reactivity of metals in water

  Potassium - very vigorous, catches fire, explosions

  Sodium - vigorous, faster reaction, fizzes

  Lithium - fizzes and floats

  Calcium - very rapid reaction but slower than above
• Why is lithium more reactive than gold?

  -it easily makes positive ions

  -by loosing an electron

  so the reactivity of metals is linked to their tendency to make positive ions
• Reactivity if metals in acids 


  Potassium, sodium and lithium - dangerously fast reaction

  Calcium - extremely vigorous

  Magnesium - rapid

  zinc - quite rapid Iron - quite slow

  Copper - no reaction
• Extraction is metals and reduction 


  -Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.

  -Metals less reactive than carbon can be extracted from their oxides by reduction with carbon.
• Oxidation & reduction 


  Oxidation - loss of electrons reduction - gain of electrons
• Displacement reaction 


  Iron displaces copper from it's compound

  Iron (Fe) + Copper sulfate (CuSO4)

  = Copper(Cu) + Iron Sulfate (FeSO4)
• Half equation for Magnesium 


  Mg --> Mg(2+) + 2e-

  -atom forms magnesium ion and 2 electrons

  -Magnesium has been oxidised as it has lost electrons
• S + 2e- --> S2-

  Here a sulfur atom has gained 2 electrons and formed a sulfide ion

  -sulfur atom had been reduced
• In this reaction which element has been oxidised and which has been reduced Zn + CuSO4 --> ZnSO4 + Cu

  Cu2+ Zn2+

  -We end with the ion zinc ion Zn2+ so the zinc electron must have lost 2 electrons - zinc has been oxidised

  -We start with copper ion Cu2+ and we make the copper atom Cu so copper must have gained 2 electrons - it was reduced
• What is produced when acids and metals react?


  Salts and hydrogen gas.

  E.g Magnesium + sulfuric acid --> magnesium sulfate + hydrogen
• Sulfuric acid --> ...sulfate

  Hydrochloric acid --> ...chloride
• Ionic equation 


  Tells us what happens to the ions that change
• Write the half equation for Magnesium 


  Mg --> Mg2+ + 2e-

  Magnesium becomes magnesium ions + 2 electrons because it has lost 2 electrons this is how it's written
• Redox reaction 


  When oxidation and reduction happens at the same time
• Write the ionic equation for

  Zn + 2HCl ---> ZnCl2 + H2

  Zn + 2H+ ---> Zn2+ + H2
• Acid


  -a substance that forms aqueous solutions with pH less than 7

  -they form H+ ions in water
• Alkali


  E.g soluble metal hydroxides like sodium hydroxide
• Bases


  e.g metal oxide or insoluble metal hydroxide

  (e.g insoluble metal hydroxides and metal oxides

  -a substance with a pH greater than 7
• Acid + alkali --> salt + water

  Acid + base --> salt + water

  Acid + metal carbonate --> salt + water + carbon dioxide

  these are all neutralisation reactions
• Hydrochloric acid makes the salt ...... chloride E.g Sodium chloride

  Sulfuric acid makes the salt ...... sulfate E.g Sodium sulfate

  Nitric acid makes the salt ...... nitrate E.g Sodium nitrate
• What do the following reactions make:

  -Hydrochloric acid + sodium hydroxide

  -Nitric acid + magnesium oxide

  -Sulfuic acid + calcium carbonate


  -sodium chloride + water

  -magnesium nitrate + water

  -calcium sulfate + water + water + carbon dioxide
• Which substance would you react to make magnesium nitrate?

  Nitric acid + magnesium hydroxide
• Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates. The solid is added to the acid until no more reacts and the excess solid is filtered off to produce a solution of the salt.
• Acid + base --> salt + water

  sulfuric acid + copper oxide --> copper sulfate + water
• Salt solutions


  Can be crystallised to produce solid salts
• Producing solid salts from salt solutions


  1. Start with a fixed volume of dilute sulfuric acid in a beaker (this is the limiting reactant)

  2. Heat this with a bunsen burner until it's almost boiling

  3. Use a spatula to add small amounts of copper oxide to the acid

  4. Stir the solution using a glass rod

  5. You'd get the formation of the copper sulfate solution which is blue so solution would turn blue

  6. If the copper oxide disappears then it has all reacted

  7. Add more copper oxide until some powder remains at the bottom of the container

  8. Now all of the acid has reacted, copper sulfate is formed and the solution is now neutral

  9. To remove the unreacted copper oxide you need to filter it- use a filter funnel and filter paper

  10. Transfer the copper sulfate solution into an evaporating dish

  11. Use a water bath to evaporate water from the solution

  12. Let it cool (24 hours)

  13. Remove crystals and pat dry, now you have pure, dry copper sulfate crystals
• Universal indicator


  -chemical that changes colour depending on weather it's an acid or an alkali

  -the colour change depends on the strength of the acid (their pH)
• pH probe


  measure pH and gives exact number
• Acids produce hydrogen ions (H+ ) in aqueous solutions.

  Aqueous solutions of alkalis contain hydroxide ions (OH– )

  In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water. represented by equation:

  H+(aq) + OH-(aq) ---> H2O (l)
• Concentrations of solutions


  High(concentrated) - more solute per given volume E.g 50g/dm^3

  Low(dilute) - E.g 5g/dm^3
• Strength of acids


  -measured in pH 0-6 in acids
• Strong Acid


  -completely ionised in aqueous solution

  -Examples hydrochloric, nitric and sulfuric acids.
• Weak acid


  -partially ionised in aqueous solution

  -Examples ethanoic(vinegar) , citric(fruit e.g lemns) and carbonic acids(fizzy water
• Hydrochloric acid is hydrogen chloride dissolved in water

  when it's dissolved in water it breaks down into hydrogen and chloride ions. This is called ionisation
• High concentration of hydrogen ions makes strong acids.

  Hydrogen ion concentration gets greater everytime we drop in pH

  drop in pH of 1 gives a 10x increase in hydrogen ions

  so pH 3 --> pH 1 thats 2 drops of pH so x10 x10 overall 100x concentration of hydrogen ions
• When an ionic compound is melted or dissolved in water, the ions are free to move about within the liquid or solution. These liquids and solutions are able to conduct electricity and are called electrolytes.