chemical changes

• acids react with some metals to produce salt and hydrogen
• oxidation is loss of electrons

  reduction is gain of electrons

  oxidation is gain of oxygen

  reduction is loss of oxygen
• metals react with oxygen to produce metal oxides. The reactions are oxidation reactions because the metal gain oxygen.
• when metals react with other substances, the metals for positive ions
• the reactivity of a metal is related to its tendency to form positive ions
• metals can be arranged in order of their reactivity in the reactivity series. A metal high up on the reactivity series loses electrons easily and thus is more reactive.
• potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper silver gold

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• a more reactive metal can displace a less reactive metal from a compound
• the order of reactivity can be determined from their reactions with water and dilute acids
• the non-metals hydrogen and carbon are included in the reactivity series to indicate how the metal can be extracted
• unreactive metals such as gold and silver are found in the Earth as the metal itself (native metals)
• 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 (loss of oxygen) with carbon
• a high grade ore is a rock that contains a metal compound at a high enough concentration and mass for it to be economical to extract
• bauxite - Al2O3 (used for aluminium)

  malachite - CuCO3 (used for copper)

  haematite - Fe2O3 (used for iron)
• CO3 (carbonates) have a 2- charge

  OH (hydroxides) have a 1- charge

  SO4 (sulfates) have a 2- charge

  H (hydrogen ions / protons) have a 1+ charge

  NH4 (ammonia) has a 1+ charge

  NO3 (nitrate) has a 1- charge
• reduction involves the loss of oxygen

  oxidation involves the gaining of oxygen
• oxidation is the loss of electron

  reduction is the gaining of electrons
• acids react with some metals to produce salts and hydrogen:

  • these reactions are redox (neutralisation) reactions
  • the metal is oxidised as it loses electrons
  • and hydrogen ions in the atoms are reduced and gain electrons, forming hydrogen gas
  • a salt is then formed between the metal and the acid remainder
• acids are neutralised by alkalis (soluble bases) and bases
• acid + alkali -> salt + water
• acid + metal oxide -> salt + water
• acid + metal -> salt + hydrogen
• acid + carbonate -> salt + water + carbon dioxide
• pure, dry salts:

  1. measure 20cm3 of acid into a beaker
  2. gently heat to boiling point of the acid to give the acid molecules more energy and increase rate of reaction
  3. at boiling point remove the acid from the heat
  4. add metal oxide in excess to make sure all the acid has reacted, stirring as you add
  5. pour solution through a filter funnel into a conical flask to remove excess
  6. in an evaporating dish, gently heat the salt solution to evaporate the water, leaving a little behind
  7. place the dish in a dry room temp room
  8. allow the rest of the water to evaporate slowly, encouraging crystallisation
• acids produce H+ ions in aqueous solutions
• aqueous solutions of alkalis contain hydroxide ions (OH-). Alkalis are soluble bases
• the pH scale is a measure of the acidity or alkalinity of a soultion
• in a neutralisation reaction between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water
• ionic equation for neutralisation:

  (H+) + (OH-) -> H20
• pH can be measured using universal indicator or a pH probe
• a strong acid is completely ionised in an aqueous solution (eg hydrochloric acid, nitric acid and sulfuric acid)
• a weak acid is only partially ionised in an aqueous solution (eg ethanoic acid, citric acid and carbonic acid)
• concentration refers to how many acid molecules there are per unit volume of solution
• a solution that is dilute has less molecules of acid per unit volume
• a solution that is concentrated has more molecules of acid per unit volume
• for a given concentration of aqueous solutions, 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 or solution are able to conduct electricity and are called electrolytes
• electrolyte - an ionic compound that is molten or dissolved in solution, and has ions which are free to move about and so conducts electricity