rp 5: rates of reaction

• disappearing cross:

  1. use a measuring cylinder to put 10 cm3 sodium thiosulfate solution into a conical flask
  2. place conical flask onto a black cross
  3. add 10 cm3 hydrochloric acid
  4. swirl solution & start a timer
  5. stop the timer when u can no longer see the cross
  6. repeat experiment using lower concentrations of sodium thiosulfate solution
  7. repeat experiment & calc mean values
• what is reproduceability?

  a finding is reproduceable if it can be repeated by another person using a different technique/equpiment & still get the same result
• volume of gas produced by a reaction:

  1. use a measuring cylinder to place 25 cm3 hydrochloric acid into a conical flask
  2. attach conical flask to a gas syringe
  3. add a 1 cm strip of magnesium to the hydrochloric acid
  4. start a timer
  5. every 30 seconds measure the volume of hydrogen gas in the gas syringe until no more hydrogen is given off
  6. repeat experiment using diff concentrations of hydrochloric acid
• why does sulfur make the solution cloudy?

  it's a precipitate (solid formed in a solution during a chemical reaction)
• what solid is formed in the disappearing cross practical?

  sulfur
• what observations could be made from the reaction between Mg(s) & HCl(aq)?

  • fizzing
  • magnesium dissolves
  • heat given off
  • change in pH