Chemical Reaction End Point Timer. - page 1
Keywords: Physics Chemistry Practical Build device end point timer
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 1 of 9 pages: 1 2 3 4 5 6 7 8 9
Chemical Reaction End Point Timer.
I am going to build and test a device to detect the end of a chemical reaction. I chose this because when I was recently doing an experiment where I had to judge by eye when a solution had become opaque, to tell when it had finished reacting. I found it quite difficult to do accurately and was interested in finding out how much the accuracy of your results increases when you use to light sensor to tell when the reaction has finished.
I will be measuring the amount of light coming through a solution of hydrochloric acid and sodium thiosulphate reacting together.
hydrochloric acid + sodium thiosulphate → sodium chloride + sulphur dioxide + sulphur + water
2HCl + Na2S203 → 2NaCl + SO2 + S + H2O
This solution gradually becomes opaque during the reaction. I am going to use a light dependant resistor in a potential divider circuit and a digital multimeter; these will give me more accurate results than a mechanical circuit and analogue multimeter. I will compare these results against the time I think the reaction has taken when I measure it by eye.
I am going to use a bright LED and a sensitive LDR to measure the amount of light coming through the solution. The LDR needs to be sensitive to pick up the light from an LED through the solution and its container, I have decided to use an LED as the light source because they are quite small so the light won’t travel around the container and affect the LDR’s reading as much as if I was using a larger light source like a light bulb. I will be using a potential divider circuit containing one variable (the LDR) and one fixed resistor and measuring the difference in the voltage across the fixed resistor to obtain my results.
A potential divider circuit works by having something change the amount of resistance on a resistor in a circuit, so that the output voltage changes by the same amount. This can be measured to tell you the amount that the resistance changed, and so tell you the change in whatever caused the resistance to change. For example a potential divider circuit controls the volume control knob on a radio. The input voltage of the radio signal is always the same, so to change the volume, when you turn the knob a sliding contact connected
Last 5 comments…
There have been no comments posted for this article, but you need to register if you want to be the first!