chemical tests

• test for hydrogen


  squeaky pop - lighted splint
• test for oxygen


  relight a glowing splint
• test for carbon dioxide

  turns limewater cloudy
• test for chlorine gas

  bleaches damp blue litmus paper white
• test for ammonia gas


  has a sharp smell - makes damp red litmus paper turn blue + forms white smoke (ammonium chloride) when reacting with hydrogen chloride
• what is formed in neutralisation

  water
• what is formed when metals and acids react

  hydrogen and a salt
• what is formed when metal oxide (base) and an acid reacts

  water and salt
• what is formed when metal carbonates react with acid

  salt and carbon dioxide
• flame colour of lithium

  crimson
• flame colour of sodium

  yellow
• flame colour of potassium

  lilac
• flame colour of calcium

  red
• flame colour of barium

  green
• flame colour of magnesium

  no colour
• aluminium ion + sodium hydroxide

  forms white precipitates + might dissolve if a lot is added
• calcium ions + sodium hydroxide

  forms white precipitates
• magnesium ions + sodium hydroxide

  forms white precipitates
• copper ions + sodium hydroxide

  forms blue precipitates
• iron(ii) ions + sodium hydroxide

  forms green precipitates
• iron(iii) ions + sodium hydroxide

  forms brown precipitates
• chloride ions + silver nitrate

  forms white precipitate
• bromide ions + silver nitrate

  forms cream precipitate
• iodide ions + silver nitrate


  forms yellow precipitate
• how to tell if a solution has sulfates

  add hydrochloric acid, then barium chloride solution - produces white precipitate of barium sulfate
• reaction of acid and alkali

  acid + alkali --> salt + water
• ammonia forms a white smoke of ammonium chloride when hydrogen chloride gas from concentrated hydrochloric acid is held near is
• halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. sliver chloride is white, silver bromide is cream and silver iodide is yellow
• sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid
• ammonia dissolves in water to produce an alkaline solution. it is used to produce ammonium salts
• H+ is acidic, OH- is alkaline
• soluble salts can be made from acids by reacting them with:

  • metals - not all metals are suitable, some are too reactive and others are not reactive enough
  • insoluble bases - the base is added to the acid until no more will react and the excess solid is filtered off
  • alkalis - an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution
• salt solutions can be crystallised to produce solid salts
• insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed. precipitation can be used to remove unwanted ions from solutions, eg. in treating water for drinking or in treating effluent
• substances needed to make a named insoluble salt:

  • silver nitrate solution
  • sodium chloride solution
  • potassium chloride solution
  • ammonium chloride solution
• it is not always possible to obtain the calculated amount of product because:

  • the reaction may not go to completion because it is reversible
  • some of the product may be lost when it is separated from the reaction mixture
  • some of the reactants may react in ways different from the expected reaction
• increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically - increases rate of reaction
• increase the concentration/pressure/surface area of reactants in solutions increases the frequency of collisions - increases rate of reaction
• if temperature is raised

  • yield from endothermic - increases
  • yield from exothermic - decreases
• if temperature is lowered

  • yield from endothermic - decreases
  • yield from exothermic - increases