Reactivity of acids

• Acid:


  An acid is a substance that produces hydrogen ions in an aqueous solution
• Alkali:


  An alkali is a substance that produces hydroxide ions in an aqueous solution
• pH scale in relation to hydrogen concerntration


  Diagram:

  
• Strength of acids


  Strength of acids is dependent on how the molecules in the acid behave when dissolved in water

  Strong acids - All molecules are completely ionised/ dissociated - all of the molecules break into ions in the water

  Weak acids - The molecules are only partially ionised in water - only a small fraction of the molecules break into ions in water
• Concentration calculations


  Volume is measured in decimetres cubed. A decimeter is 1000cm cubed.

  Concentration is in mols/dm cubed

  
• Naming salts


  1st word - Metal from base

  2nd word - from the acid

  Hydrochloric acid - Chloride

  Sulfuric acid - Sulfate

  Nitric acid - Nitrate
• Reactions of metals and acids

  Metal + acid -> metal salt + hydrogen

  Metal oxide + acid -> metal salt + water

  Metal hydroxide + acid -> metal salt + water

  Metal carbonate + acid -> metal salt + water + carbon dioxide
• Concentration of acids


  Concentrated -A solution in which there is a lot of solute dissolved

  Dilute - A solution in which there is a small amount of solute dissolved
• Reactions of metals and acids


  Reactions of metal and acids are neutralisation, displacement and redox reactions.

  Metals below hydrogen in the reactivity series don't react as they can't displace hydrogen.

  Metals below carbon have a slow reaction

  Calcium, magnesium and aluminium have a vigorous reaction

  Potassium, sodium and lithium have a violent reaction

  
• Titrations


  Titrations are a very accurate experimental technique that can be used to find the concentration of a solution by reacting it with a solution of a known concentration. Titrations are often used to find the concentration of acids or alkalis
• Equipment for a titration experiment

  A pipette is a glass tube designed to measure a specific volume of a solution very accurately.

  A burette is a glass tube with a tap with markings to show the volume to the nearest 0.1 cm cubed

  
• Titration method


  1. A known volume of a solution of an acid or alkali is measured using a pipette and placed into a conical flask
  2. A few drops of a suitable indicator are added. For most acid-alkali titrations, methyl orange or phenolphthalein is suitable
  3. The other solution, acid or alkali, is added to the conical flask from a burette
• Titration method 2


  4. The solution is added from the burette until the indicator changes colour (the endpoint). The solution is added dropwise around the point where the indicator changes colour to ensure the exact volume required is used

  5. The volume added from the burette is recorded

  6. The experiment is repeated until concordant results are achieved. The mean volume is found using the concordant results