Acids & Bases

Acids & Bases

1. Acids

   • acids are chemicals when dissolved in water, produce hydrogen ions (produce hydronium ions in solution)
   • Properties of Acids
     • litmus turns red
     • universal indicator turns red/orange/yellow
     • metals react with acids to produce a salt and hydrogen gas
     • bases react with acids to produce a salt and water
     • carbonates react with acids to produce salt, water and carbon dioxide
     • taste sour e.g. vinegar contains acetic acid, lemon contains citric acid and soda water contains carbonic acid

2. bases

   • bases are chemicals that react with acids to produce a salt and water
   • alkalis are soluble bases and are hydroxides of group 1 and 2 excluding Be and Mg e.g. Li(OH)2, NaOH and KOH
     • alkalis are chemicals when dissolved in water, produce hydroxide ions
   • properties of bases
     • litmus turns blue
     • universal indicator turns blue/purple/bluey green
     • acids react with bases to produce a salt and water
     • ammonium salts react with bases to produce a salt, ammonia and water. Therefore, ammonium salts are weakly acidic
       • ammonia is a pungent smelling gas. It is soluble in water to produce a solution, which is ammonia solution/ammonium hydroxide

3. Describing acids and bases

   • weak and strong
     • acids and bases ionise (form ions in water)
     • Strong: when most of the chemical ionises it is a strong base/acid
       • Strong acids: HNO3, HCL, H2SO4
       • Strong bases: Group 1 and 2 hydroxides excluding Be and Mg
     • Weak: If only a little of the chemical ionises it is called a weak acid/base
   • Dilute and concentrated
     • describes how many moles of the acid and base are in one litre of the solution
     • Dilute: a solution with less than 1-2 mol/L
     • Concentrated: more than 1-2 mol/L
   • Diprotic
     • H+ can be described as a proton. This is because it only has 1 proton and 1 electron. When it becomes an ion it loses its electron
     • a diprotic acid can give 2 protons when it dissolves in water e.g. H2SO4
     • Triprotic is when an acid gives 3 protons when dissolved e.g. H3PO4 and monoprotic acids can give 1 e.g. HNO3

4. Arhenius

   • Classifying oxides
     • Acidic oxides (non-metal)
       • react with water to produce acids
       • oxides of most non-metals
     • Basic oxides (metal)
       • react with acids to make a salt and water
       • oxides of most metals
     • Neutral oxides
       • Do not react with water to form acids
       • Do not react with acids
       • Oxides of a few non-metals, H2O, CO and NO
     • non-metal oxides are acidic and neutral
     • Metal oxides are basic

5. PH

   • pH is a measure of how acidic or alkaline a solution in water is. It is a number that comes from the concentration of H+ ions in the water
   • pH is dependent on temperature (25 degrees)
   • pH of acids = below 7
   • pH of bases = above 7
   • Neutral = 7
   • formulas
     • pH = - Log10[H+]
       • [H+] in m/L
     • [H+] = 10^-pH
   • decreasing the concentration of H3O+ ions by a factor of 10 results in an increase in pH by one unit. A solution with pH = 1 has 10 times the concentration of hydrogen ions as one of pH = 2
     • acidic solutions contain a greater concentration of H+ ions than OH- ions
       • basic solutions contain a greater concentration of OH- ions than H+ ions

6. Ionisation of water

   • Water is a weak electrolyte and very few molecules ionise to form H+ and OH-. The equation for the ionising of water is:
   • used to calculate the pH of any solution of either the [H+] of the [OH-]
     • Kw: 1 x 10^-14 = [H+] x [OH-]

7. Dilutions

   • this formula can only be used when WATER is added or removed from a solution
   • C1V1 = C2V2
     • *** when finding the VOLUME OF WATER ADDED V2-V1

8. Electrolytes

   • Strong Electrolytes
     • Chemicals that will completely ionise/dissociate when put in water (e.g. strong acids/bases/ionic solids)
     • e.g. all the NaCl(s) put into water will dissolve and dissociate. All the NaCl will break into ions (bonding)
     • e.g. all the HCl(g) put into water will dissolve and ionise. HCl will go into the water and react to produce H3O+ and Cl- (bonding)
     • e.g. Insoluble AgCl (s) put into water will only have a very small amount dissolve This small amount will completely dissociate to form Ag+ and Cl-
     • examples of chemicals that are strong electrolytes:
       • soluble and insoluble ionic compounds
       • Strong acids
   • Weak Electrolytes
     • Chemicals that only partially ionise or dissociate when put in water
       • shown by double headed arrow
         • e.g. all the molecules of CH3COOH (l) put into water will dissolve but only a few will ionise. Most of the molecules will go into the water and only a few H3O+ and CH3COO-
     • Examples of weak electrolytes
       • ammonia (NH3)
       • weak acids
   • Non-electrolytes
     • chemicals that do not ionise or dissociate when put in water
       • Do not provide any charged particles at all
     • e.g. all the molecules of sugar put into water will dissolve but none will ionise. 100% of molecules go into the water
     • examples of non electrolytes are covalent substances except ones already mentioned

9. Electrical conductivity

   • solutions ability to conduct electricity depends on:
     • The strength of the electrolyte. Strong electrolytes have the greatest conductivity.
     • the concentration of the ions. The larger the concentration of ions, the more free moving charged particles and therefore, greater conductivity

10. Ionisation of multiprotic acids

    • e.g. sulfuric acid is a diprotic acid. The ionisation of the acid occurs in 2 steps.
      • The first ionisation is almost complete (H2SO4 is a strong electrolyte and therefore it completely ionises in water).
        • The second ionisation however is only partial. The chemical species present in a dilute solution of sulfuric acid are a small number of HSO4-, a large number of H3O+ and a large number of SO42-
    • e.g. phosphoric acid
      • no step is 100% complete (as H3PO4 is a weak electrolyte). Each step is successively less successful. All species are present.

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