C6

C6

1. Acids and alkalis

   • Indicators turn blue in alkalis and red in acids
   • Pure acid compounds can be solids, liquids or gases
   • Pure liquid acid: Sulfuric acid and nitric acid
   • Pure gas acid: hydrochloric acid
   • Pure solid acid: citric acid and tartaric acid

2. Reactions of acids

   • Metal + acid -> salt + hydrogen
   • Metal oxide + acid -> salt + water
   • Metal carbonate + acid -> salt + water + carbon dioxide
   • Acids give negative ions

3. Reacting amounts

   • The relative atomic mass of a compound is the sum of the relative atomic masses of the compounds
   • RAM Mg = 24, RAM Cl = 35.5
   • MgCl2 = 24 + (35.5 x 2) = 95

4. Titrations

   • When an acid reacts with an alkali it becomes neutral
   • A titration is used to measure the volume of acid and alkali that exactly react together
   • An indicator is added so you can see when the neutralisation happens. The indicator suddenly changes color at the end of the titration
   • It is repeated to make sure results are close together

5. Neutralisation

   • When an acid reacts with an alkali a salt and water is made
   • All acids contain H+ ions when they are dissolved in water
   • All alkalis contain hydroxide ion OH- when they are dissolved in water
   • In neutralisation reactions the hydroxide ions and hyrdogen ions join up to form water H2O
   • The positive ion from the alkali and the negative ion from the acid makes the salt

6. Energy changes

   • Exothermic reactions give out heat energy
   • Endothermic reactions take in heat energy

7. Crystallisation

   • It is used to purify impure solid crystals
   • 1 Dissolve the product in a small amount of hot water
   • 2 Filter off any impurities that don't dissolve. The solution that comes through is the filtrate
   • 3 Evaporate - the filtrate starts to crystallise as some of the water evaporates off. Cool the filtrate while the product continues to evaporate
   • 4 Filter off the crystals, leaving any solid impurities in the solution
   • 5 Dry the crystals in a dessicator or an oven

8. Percentage yield

   • The actual yield is the mass of the product measured at the end of the experiment
   • The theoretical yield is the predicted yield
   • Percentage yield = actual yield/theoretical yield x 100

9. Rate of reaction

   • Rate of reaction is the amount of a product produced or the amount of the reactant used up
   • If the reaction makes a gas
     • Measure the volume of gas made at set times
     • Measure the decrease in mass of the flask as the gas leaves the reaction
   • If the reaction makes a solid
     • Measure the time it takes you to not be able to see a cross underneath the burret or flask
   • Factors of rate of reaction
     • Frequency of collisions
       • The amount of collisions in a given amount of time
     • Percentage of successful collisions
       • If the atoms collide they have a succesful reaction
     • Temperature
       • Particles vibrate so they are more likely to collide - higher temperature higher rate
       • The particles have higher kinetic energy when temperature is higher so they are more likely to have a successful collision
     • Concentration of liquid
       • More particles in a volume so higher frequency of collisions
       • Higher pressure = higher concentration
     • Catalyst
       • Catalyst are chemicals that speed up reactions
       • They reduce the activation energy for a reaction
       • Affects percentage of successful collisions
     • Surface area of the solid reactant
       • More open area to react with - higher frequency of collisions

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