Topic 3 chemical changes

• That solutions with a pH of less than 7 are acidic, solutions with a pH of more than 7 are alkaline and solutions with a pH of exactly 7 are neutral.
• acids release

  H+ ions
• The reaction between an acid and an alkali is called neutralisation.
• alkalis absorb H+ ions
• Acid + Alkali → Salt + Water
• base

  is a substance that reacts with an acid to form only a salt and water.
• alkali

  is a base that is soluble in water.

  -release OH- ions in a solution

  - the higher the concentration of hydrogen ions in a solution, the lower the pH, and the higher the concentration of hydroxide ions in a solution, the higher the pH.
• in neutralisation reactions

  water is produced when hydrogen ions (from an acid) react with hydroxide ions (from a base).
• That acids that ionise completely are strong acids and acids that partially ionise are weak acids.
• That the concentration of an acid measures how much acid there is in a litre of water.
• That a concentrated acid has a large number of acid molecules compared to the volume of water and a dilute acid has a small number of acid molecules compared to the volume of water.
• That the pH of a solution changes by 1 if the H+ ion concentration changes by a factor of 10.
• the reaction of an acid with a metal hydroxide or a metal oxide forms a salt and water.
• an acid will react with a metal to produce a metal salt and hydrogen.
• test for hydrogen 


  placing a lit splint in to a test tube containing hydrogen will produce a 'squeaky pop' sound.
• what's formed in the reaction of a metal carbonate and an acid

  carbon dioxide, a salt and water
• test for carbon dioxide

  carbon dioxide will turn a solution of limewater cloudy if it is bubbled through it.
• common salts of sodium, potassium and ammonium will dissolve (are soluble) in water.
• do nitrates salts dissolve in water

  yes
• That common chloride salts, except those of silver and lead, will dissolve in water.
• That common sulfate salts, except those of barium, lead and calcium, will dissolve in water.
• That common carbonates and hydroxides, except those of sodium, potassium and ammonium, will not dissolve (are insoluble) in water
• That excess insoluble reactant is used in the preparation of a soluble salt in order to ensure that all the acid in the solution has reacted to produce a salt.
• That excess insoluble reactant is removed at the end of the preparation of a soluble salt to make sure that the salt produced is pure, so the remaining solution contains only the salt and water.
• That a dissolved or molten ionic compound will break down if a current is passed through it.
• That electrolytes are

  are molten or dissolved ionic compounds.
• what happens during electrolysis?

  the positive ions (cations) in the electrolyte move towards the negative electrode (cathode) and the negative ions (anions) move towards the positive electrode (anode).
• what happens to positive ions in electrolysis?

  positive ions are reduced (gain electrons) and negative ions are oxidised (lose electrons) at the electrodes.
• what happens when an ionic compound, containing two elements, is melted and electrolysed?

  the metal forms at the negative electrode and the non-metal forms at the positive electrode.
• electrolysed molten lead bromide forms lead (at the cathode) and bromine gas (at the anode).
• what are the products of the electrolysis of an aqueous solution using inert electrodes determined by?

  the reactivity of the elements.
• what can water break down into in electrolysis?

  That water can break down into H+ and OH ions and these ions can be discharged in electrolysis.
• what happens when the metal ion dissolved in the aqueous solution forms an elemental metal that is more reactive than hydrogen?

  hydrogen will be formed at the cathode.
• what happens if the solution contains halide ions?


  then the halogen will be formed at the anode, but, if no halides are present, then oxygen and water will be produced.