chemical changes

• metals react with oxygen to produce metal oxides. the reaction are oxidation reactions because the metals gain oxygen
• oxidation is the:

  • the loss of electrons
  • gain of oxygen
  • loss of hydrogen
• reduction is the:

  • gain of electrons
  • loss of oxygen
  • gain of hydrogen
• • Metal atoms form positive ions by loss of electrons when they react with other substances
• • A metal that is high up on the series loses electrons easily and is thus more reactive than one which is lower down on the series
• The metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper can be put in order of their reactivity from their reactions with water and dilute acids.
• A more reactive metal can displace a less reactive metal from a compound.
• Unreactive metals such as gold are found in the Earth as the metal itself
• 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.
• Reduction involves the loss of oxygen
• Acids react with some metals to produce salts and hydrogen.
• acids are neutralised by alkalis ( soluble metal hydroxides ) and bases ( insoluble metal hydroxides and metal oxides) to form salts and water
• acids are neutralised by metal carbonates to produce salts water and carbon dioxide
• 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 it no longer reacts and the excess solid is filtered off to solve the salt
• 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 a universal indicator or a pH probe.
• A solution with pH 7 is neutral.
• Aqueous solutions of acids have pH values of less than 7
• aqueous solutions of alkalis have pH values greater than 7.
• In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water.
• The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator.
• A strong acid is completely ionised in aqueous solution.
• A weak acid is only partially ionised in aqueous solution.
• As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10.
• electrolysis is a process in which an electric current is passed through a solution or molten substance to produce chemical reactions.
• in electrolysis the electric current causes ions to move from one electrode to the other, resulting in chemical reactions and the formation of new products
• purpose of electrolysis in metal extraction: to separate metal ions from a mixture of metal oxides
• electrolysis is useful for extracting metals that cannot be obtained through reduction or smelting such as aluminium and magnesium
• in electrolysis:

  • a solution or molten substances are attracted to electrodes of opposite charge
• • positive ions move to the negative electrode, cathode
  • gain electrons
  • form a deposit of pure metal
• • negative ions move to the positive electrode, anode
  • lose electrons
  • form a gas or other products
• the first step of electrolysis

  set up apparatus, which consists of two electrodes, a power source and a container of metal ions
• the second step of electrolysis

  pass an electric current through the metal ions, causing the positive metal ions to be attracted to the cathode and deposited as pure metal, and the negative metal ions to be attracted to the anode
• the third step of electrolysis

  removing the pure metal deposits from the cathode an discarding the products produced at the the anode
• examples of metals that can be extracted through electrolysis

  • magnesium
  • copper
  • silver
  • gold
• advantages of using electrolysis

  • the ability to extract metals that cannot be obtained through reduction or smelting
  • high efficiency
  • purity of the metal produced
  • ability to control and obtain a consistent product
• disadvantages of electrolysis

  • high cost of equipment and energy
  • need of constant supply of electric current
  • generation of waste products that must be disposed of safely
• safety precautions for electrolysis

  • avoid electrical shock
  • chemical burns
  • wear protective clothing and equipment
  • work in a well ventilated area