Rates of reactionIB MYP Sciences: Mind map

Exam questions on Rates of reaction

1. A student in Auckland adds magnesium ribbon to dilute hydrochloric acid in a flask and collects the hydrogen gas in a gas syringe, recording the volume every 10 seconds. She plots the volume of gas against time. The line is steepest at the start and becomes horizontal after about 120 seconds.
   Explain why the reaction is fastest at the start.2 marks
2. A student in Dublin drops one effervescent vitamin tablet into 200 cm³ of water at 10 °C and times how long it takes for the fizzing to stop. It takes 120 s. She repeats the experiment with water at 40 °C and it takes 35 s. The tablets are the same size.
   The student repeats the experiment at 10 °C using a tablet that has been crushed into a powder. Predict how the time for the fizzing to stop will change and explain your prediction.2 marks
3. A student in Cape Town investigates how the concentration of sodium thiosulfate solution affects its reaction with hydrochloric acid, which makes a cloudy yellow precipitate of sulfur. She stands the flask on a cross drawn on paper and times how long it takes for the cross to disappear when she looks down through the liquid. For sodium thiosulfate solutions of concentration 0.10, 0.05 and 0.025 mol dm⁻³, the times are 40 s, 80 s and 160 s.
   Describe the pattern in the results and explain it using collision theory.3 marks