Which two variables should the student keep the same to make the investigation a fair test? Tick two boxes.
solid
sulfur
Plan an investigation to show how the concentration of the sodium thiosulfate solution affects the rate of the reaction with dilute hydrochloric acid.
Your plan should give valid results.
method
• measure volume of sodium thiosulfate
• place sodium thiosulfate in
• measure volume of hydrochloric acid
• place on
• add hydrochloric acid to (conical) flask
• swirl
• start
• measure time for cross to become no longer visible
• repeat for different concentrations of sodium thiosulfate
control variables
• of hydrochloric acid
• volume of hydrochloric acid
• of sodium thiosulfate solution
volume
conical flask
cross
stopwatch
measuring cylinder
concentration
which is an insoluble