disappearing cross reaction

• investigating the effect of concentration on the rate of reaction
• hypothesis is a proposal that can explain an observation , it has to be testable
• ! reproducability is hard because people may have different eye sights one way this is reduced is by using the same size cross
• sodium thiosulfate + hydrochloric acid = sulfur ( solid )
• method

  1. using a measuring cylinder measure 10cm$^3$ of sodium thiosulfate into a conical flask
  2. place the conical flask on top of a black cross
  3. add 10cm $^3$ of hydrochloric acid
  4. swirl and start the timer
  5. look down throught the top of the flask to see when the black cross disappears and stop the timer
  6. repeat using lower concentrations of sodium thiosulfate
  7. repeat and calculate a mean
• the reaction creates a cloudy solution called turbidity