Chemical changes

• Metal + Oxygen -> Metal oxide

  • This is an oxidation reaction because the metals gain oxygen
• Reduction - loss of oxygen
• When metals react with other substances the metal atoms form positive ions. The reactivity of a metal is related to its tendency to form positive ions.
• Reactivity series

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium

  CARBON

  • Zinc
  • Iron

  HYDROGEN

  • Copper
  • Silver
  • Gold
  • Platinum
• A more reactive metal can displace a less reactive metal from a compound.
• • Less reactive metals like zinc, iron and copper won't react with water
  • Copper won't react with acids
• More reactive the metal:

  • More vigorous reaction
  • More bubbles produced
  • Greater temperature change
• 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

  Is

  Loss (of electrons)

  Reduction

  Is

  Gain (of electrons)
• Spectator ions

  • Ions that don't change in the reaction
• Metal + Acid -> Salt + Hydrogen
• Metal + Water -> Metal Hydroxide + Hydrogen
• Acids are neutralised by alkalis (e.g. soluble metal hydroxides) and bases (e.g. insoluble metal hydroxides and metal oxides)
• Acid + Alkali -> Salt + Water
• Acid + Metal Carbonate -> Salt + Water + Carbon dioxide
• Salts produced by acids

  • Hydrochloric acid: Chlorides
  • Nitric acid: Nitrates
  • Sulfuric acid: Sulfates
• • 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.
  • Salt solutions can be crystallised to produce solid salts.
• Making pure, dry samples of soluble salts using an insoluble base and an acid

  1. Add acid to beaker and gently warm acid using a bunsen burner
  2. Add insoluble base to the acid a bit at a time, and swirl, continue adding until it is in excess and no more reacts
  3. Filter out excess solid using filter paper and funnel to get the salt solution and place on an evaporating basin
  4. Gently heat the solution using a water bath to evaporate some of the water and then leave solution to cool and crystallise
  5. Pat dry gently crystals using filter paper
• • Acids produce hydrogen ions (H+) in aqueous solutions
  • Aqueous solutions of alkalis contain hydroxide ions (OH–)
• The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.

  • pH 7 - neutral
  • Less than pH 7 - acidic
  • More than pH 7 - alkaline
• In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water.

  • H+ (aq) + OH- (aq) -> H2O (l)
• The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator
• Indicators

  • Phenolphthalein
  • In acids: Colourless
  • In alkalis: Pink
  • Methyl Orange
  • In acids: Red
  • In alkalis: Yellow
• Titrations

  1. Using a pipette and pipette filler, add 25 cm3 of alkali to a conical flask
  2. Add three drops of phenolphthalein indicator
  3. Place conical flask on a white tile to see colour change more clearly
  4. Fill a burette with acid of known concentration and record initial volume of acid in burette
  5. Perform a rough titration to get an approximate idea of where the solution changes colour.
  6. Using the burette, add acid to alkali a bit at a time, regularly swirling flask. Go slowly near end-point
  7. Indicator changes colour from pink to colourless
  8. Record final volume of acid in burette to calculate volume of acid used to neutralise the alkali
  9. Repeat the whole experiment and calculate a mean
• • A strong acid is completely ionised in aqueous solution. Examples of strong acids are hydrochloric, nitric and sulfuric acids.
  • A weak acid is only partially ionised in aqueous solution. Examples of weak acids are ethanoic, citric and carbonic acids.
  • A dilute acid has small amount of acid per unit volume
  • A concentrated acid has a greater amount of acid per unit volume
• The stronger an acid, the lower the pH.
• As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10.
• 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.
• Passing an electric current through electrolytes causes the ions to move to the electrodes.

  • Positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode).
  • Ions are discharged at the electrodes producing elements. This process is called electrolysis.
• PANIC

  • Positive
  • Anode
  • Negative
  • Is
  • Cathode
• When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.
• • Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.
  • Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
• • Aluminium oxide is extracted from the ore bauxite
  • Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode (anode).
  • Aluminium oxide has a very high melting point so mixed with cryolite to lower it, decreasing energy used
  • Positive electrode made from carbon needs to be continually replaced as it reacts with oxygen to produce carbon dioxide
• • The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved.
  • At the negative electrode (cathode), hydrogen is produced if the metal is more reactive than hydrogen.
  • At the positive electrode (anode), oxygen is produced unless the solution contains halide ions when the halogen is produced.
  • This happens because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged.
• Red Cat An Ox

  • Reduction Cathode
  • Anode Oxidation
• When hydrogen is produced in aqueuous solution electrolysis at cathode

  • 2H+ + 2e- -> H2
• When oxygen produced in aqueous solution electrolysis at anode

  • 4OH- -> O2 + 2H2O + 4e-