Chemical Reaction End Point Timer. - page 8
Keywords: Physics Chemistry Practical Build device end point timer
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 8 of 9 pages: 1 2 3 4 5 6 7 8 9
starting the timer at the same time and it was also difficult to make the first measurement as it took nearly 10 seconds to completely empty the pipette. To solve this I got someone else to assist me by pouring the chemicals for me.
I received some help from my teacher with setting up the circuits and soldering the integrated resistor onto the LED. I also used my textbook Advancing Physics AS to help with my explanation of the physics of potential dividers and LDRs.
I think that my sensor is well suited to carrying out its intended function. As I discovered from my results it is much more accurate at detecting the end of a chemical reaction than the judging by eye technique. The smallest change in voltage my sensor could record was 0.001 volts however due to the random error I only took readings to 2 decimal places. The stopwatch could measure changes of 0.01 seconds but I only took readings accurate to 1 second due to the limits of my response time.
These accuracies gave good graphs from which you can easily measure the time in seconds that the reaction took. I don’t think there is much need for a greater accuracy than this in these experiments especially as due to the method of taking the reading, any reading with a greater number of decimal places would be likely to contain error. The sensor had a quick response time as the changes in light levels had an immediate affect on the LDR and quickly transferred to the readings on the digital multimeter. The readings changed far more frequently than 10 seconds but due to the time it took for me to observe and record the readings, 10 seconds was the most frequent I could get. There didn’t seem to be any systematic bias that I could detect on this sensor although there was the random error mentioned earlier caused by movement changing light level and minimised by my cover. There also may have been some random variation in the charge coming off the mains which could have affected my results.
In short, for carrying out the type of experiment of which I was thinking when I started this project, this sensor would be extremely helpful for recording far more accurate results to an appropriate degree of accuracy. However for an experiment requiring a very high degree of accuracy it wouldn’t be
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