Presentation on theme: "Using preliminary work to choose the values of control variables"— Presentation transcript:
1Using preliminary work to choose the values of control variables Consider a simple experiment – like measuring the temperature rise in a reaction between Copper Sulphate and Magnesium powder. We will change the mass of magnesium.
2Get it clear in your mind what the following variables are: In this investigation, you will need to control some of the variables.Write down one variable that will need to be controlled.Describe briefly how a preliminary investigation could help you to find a suitable value for the control variable.You should explain how the results of this preliminary investigation will help you to decide on the best value for the control variable.The rules:Get it clear in your mind what the following variables are:IndependentDependentMass of magnesiumTemperature rise
3Now identify the control variables: Volume of Copper SulphateConcentration of Copper SulphateStarting TemperaturePick one that is easy to understandEg Volume of copper sulphateTo get the marks for this question:Choose two values for the volume – a big one and a small one would be good.I will try a volume of 10cm3 of copper sulphate and a volume of 100cm3 of copper sulphate
4Say what you will do with these two volumes: I will measure the starting temperature for both volumes. I will add one spatula of magnesium powder to each volume and measure the temperature after.It is important to say what you are going to measureTo get the final mark – say how you will decide which is the best to use.Whichever volume gives the bigger rise in temperature will be the best one to choose