SC18

• Marble Chips Practical:

  1. Put dilute hydrochloric acid inside a flask and add marble chips
  2. This releases carbon dioxide which can be collected and measured using a gas syringe (volume)
  3. Record the reading at regular time intervals
  4. Repeat the experiment with the same volume/concentration of hydrochloric acid but with powdered chalk (equal mass of previous)
• The larger the surface area, the faster the rate of reaction and the steeper the graph gradient.

  The higher the acid concentration, the faster the reaction finishes
• Sodium thiosulfate and hydrochloric acid are both clear, colourless solutions that react together to form a yellow precipitate of sulfur
• Colour Changing Practical:

  1. Measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder
  2. Use a water bath to gently heat solutions before mixing (more particle energy)
  3. Place a conical flask over a black mark then mix the heated solutions together
  4. Time how long it takes for the cloudy, yellow sulfur to cover the black mark
  5. Repeat experiment at different temperatures (same depth/volume of liquid, same solution concentrations)
• The higher the temperature, the faster the rate of reaction
• Precipitation - two clear solutions produce a precipitate which clouds the solution (Colour Changing Practical)
• Change in Mass - measure rate of reaction that produces a gas using mass balance

  • lost mass means the quicker the balance reading drops the faster the reaction
  • finished when balance value stops changing
  • if gas is harmful then use a fume cupboard for safety
• Volume of Gas Given Off - gas syringe to measure volume (Marble Chips Practical)
• Rate of Chemical Reactions:

  • Collision Frequency - how often particles collide
  • Energy Transferred - particles need to collide with enough activation energy to be successful

  These requirements are dependent on the factors temperature, concentration, pressure and surface area
• Temperature:

  • increased temperature causes particles to move faster and therefore collide more
  • more energy supplied for activation energy means more successful collisions
• Concentration/Pressure:

  • more reactant particles in the same volume (crowded) means collisions are more likely
• Surface Area:

  • larger surface area to volume ratio means more area to work on
  • collision frequency increases
• Catalyst - a substance which increases the rate of a reaction without being chemically changed or used up in the reaction
• Catalysts:

  • only small amounts are needed to catalyse large amounts of reactants
  • decrease activation energy by providing an alternative pathway requiring less energy
  • specific to certain reactions
• Enzymes - biological catalysts

  • catalyse chemical reactions in living cells
  • uses include respiration, photosynthesis and protein synthesis