Chemistry Controlled Assessment Lesson 1

Practical investigation Factors that affect the rate of reaction between sodium thiosulfate and hydrochloric acid.

What are you trying to achieve? To collect data that is meaningful, repeatable and precise. To be able to plot a graph so you need at least 6 measurements/variables. To be able to plot range bars so you need at least 3 repeats.

You are going to carry out an investigation into the rate of reaction between sodium thiosulfate and dilute hydrochloric acid. You will choose one factor and investigate this factor’s effect on the rate of reaction. What factors affect the rate of reaction? What variables might you have?

Your introduction should include all the background science that you have studied. What is meant by rate of reaction? What different factors affect the rate of reaction? Why is this? Which ones are relevant to this investigation? Use Chapter C6 of your textbook to help you What do you think is worth focussing on? – choose one variable.

Draw a diagram to explain collision theory. Relate it to your investigation.

Write a list of the variables that you could change. And, write a list of the variables that you will control. Write a couple of paragraphs about what factors affect the rate of reaction. Us your textbook (C6) to help you. Make sure that you reference your work.

Write a hypothesis and a quantitative prediction. Hypothesis: Sodium thiosulfate reacts faster with acid at a stronger concentration. Quantitative prediction: must be numerical and measurable. i.e. if the concentration of acid doubles, the time taken for the reaction to happen decreases by half.

How on earth can you make a quantitative prediction? Secondary data Preliminary work

Secondary data See secondary data presentation

Preliminary work This is your opportunity to carry out rough experiments to find out things like: What are the appropriate concentrations of acid to use? How often should I measure the variable? What temperature range will work best to give me a decent spread of data?

What are you trying to achieve? To collect data that is valid: reproducible, repeatable and precise. To be able to plot a graph so you need at least 6 measurements/variables. To be able to plot range bars so you need at least 3 repeats – remember your ranges need to be small.