Acid & Alkalis - C2

Nota:

• Acid + base = salt + water Acid + metal = salt + hydrogen Acid + carbonate = salt + carbon dioxide +water Acid + ammonia = salt

1. Acids

   Nota:

   • Substances with a pH less than 7 are acids. The more strongly acidic the solution, the lower its pH number. acids contain H+ which they can donate (proton donor)  
   1. How to test

      Nota:

      • Acidic solutions turn blue litmus paper red. They turn universal indicator paper res if they are strongly acid, and orange or yellow if they are weakly acidic.
   2. Examples

      Nota:

      • Hydrochloric HCl Nitric HNO3 Sulphuric H2SO4 Phosphoric H3PO4
2. Alkalis

   Nota:

   • Bases that dissolve in water Alkaline solutions have a pH of more than 7. The stronger the alkali, the higher the pH number
   1. How to test

      Nota:

      • Alkalis turn red litmus paper bule they turn universal indicator dark blue or purple if they are strongly alkaline, and blue-green if they are weakly alkaline
   2. Examples

      Nota:

      • Sodium hydroxide NaOH Potassium hydroxide KOH Calcium hydroxide Ca(OH)2
      1. Ammonia NH3

         Nota:

         • Even though it doesn't contain OH-, it's an alkali NH3 + H2O = NH4OH (ammonium hydroxide/ ammonia) NH4+ = Ammonium PLants need N2 as it builds protein. They take N2 out from the soil so ammonium salts are used as fertilisers.
3. Bases

   Nota:

   • Substances that can react with acids and neutralise them to make a salt and water. They are usually metal oxides or metal hydroxides. Bases can accept a H+ and neutralise an acid
4. Neutral Solutions

   Nota:

   • have a pH of 7
   1. how to test

      Nota:

      • they don't change the colour of litmus paper. they turn universal indicator green.
   2. examples

      Nota:

      • water
   3. H+(aq) + OH-(aq) = H20(l)

      Nota:

      • Neutralisation reaction (the main reaction of this topic, the other elements are spectator ions as they are not taking place in a reaction)
5. Salt

   Nota:

   • Compound made from a neutralisation process e.g. AgNO3(aq) + NaCl(aq) + AgCl(s) + NaNO3(aq) AgCl = insoluble salt
   1. Precipitation reaction

      Nota:

      • solid (insoluble salt)  is formed by mixing 2 solutions -filter and wash it They can be used to remove unwanted ions in solution.  -useful for treating drinking water and waste water.
   2. Examples

      Nota:

      • Cl- + K+ = KCl (neutral salt) SO4 2-  + Na+ = Na2SO4 (neutral salt) OH- + Fe 3+ + fe(OH)3 (neutrarl salt)