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Lab Report Chemistry IA Help [Systematic Error vs. Random Error]

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Hi Everyone,

I have an IA at the moment (about the rate of reaction for the reaction between sodium thiosulfate and hydrochloric acid) and I'm trying to write up the evaluation. However in the evaluation our teacher said we need to identify whether the weaknesses we identify are systematic or random errors and I'm really confused because I'm not 100% sure about what exactly systematic and random errors are. Here's a simplified list of the weaknesses I've identified for my particular prac and I was wondering if somebody could please just let me know if I have correctly identified the errors as either systematic or random :

- Difficult to add the reactants together and start the stopwatch simultaneously (random)

- The cross which was positioned under the conical flask, was not in the same position for each trial (no idea what type of error this is)

- The conical flask which contained the mixture of reactants was not mixed an equal amount of times in each trial for each different concentration (systematic)

- Reliability of experiment needs to be improved (systematic)

- Difficult to determine the exact moment the sulfur precipitate obscured the cross marked on the piece of paper (random)

Thank you, I would greatly appreciate some help :)!

Edited by panos

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  • Personally I would say that they are all random. This is because the error is changing across different results. A systematic error tends to be something like a "zero error" (calibration error), which effects all of the results equally.
  • For the second one I would say that because the cross is moving, it applies differently across all the different results, hence is random.
  • The third one I would disagree with you because, again, the result would depend on the number of times you stirred the rod, which differs across all of the results.
  • The fourth one had me stumped. However I read this "Random errors are considered part of the reliability of a measurement.Systematic errors are considered part of the validity of a measurement" (http://www.med.uottawa.ca/sim/data/measurement_validity.htm, pretty good for general information on this topic anyway.) Also I wouldn't use this as an error (just personally). This would be a result of errors, and what you want to improve, but does not effect the experiment, it is effected BY the experiment. You should discuss this, but in a different context.

For a systematic error you could use a calibration error, an over or under sensitive thermometer (which is over or under sensitive by a constant number or proportional %).

It would be good if someone else could confirm or deny this though. Otherwise Google search a few things, (systematic error, random error, etc.) and see if it clears it up better than me.

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  • Personally I would say that they are all random. This is because the error is changing across different results. A systematic error tends to be something like a "zero error" (calibration error), which effects all of the results equally.
  • For the second one I would say that because the cross is moving, it applies differently across all the different results, hence is random.
  • The third one I would disagree with you because, again, the result would depend on the number of times you stirred the rod, which differs across all of the results.
  • The fourth one had me stumped. However I read this "Random errors are considered part of the reliability of a measurement.Systematic errors are considered part of the validity of a measurement" (http://www.med.uottawa.ca/sim/data/measurement_validity.htm, pretty good for general information on this topic anyway.) Also I wouldn't use this as an error (just personally). This would be a result of errors, and what you want to improve, but does not effect the experiment, it is effected BY the experiment. You should discuss this, but in a different context.

For a systematic error you could use a calibration error, an over or under sensitive thermometer (which is over or under sensitive by a constant number or proportional %).

It would be good if someone else could confirm or deny this though. Otherwise Google search a few things, (systematic error, random error, etc.) and see if it clears it up better than me.

Hi,

Thank you for your help, it is very much appreciated. I'll be sure to have a further look into what you said but it seems good to me! Also do you know any systematic errors I could mention ( The thermometer is a good example except we didn't use one in this experiment). The only equipment we used with uncertainties were measuring cylinders and stop watches :)

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No, actually they're not all random. A random error is one where by doing multiple trials and averaging them you should be able to reduce it. A systematic error is something wrong with how you did the experiment.

I'd consider your errors to be:

- Difficult to add the reactants together and start the stopwatch simultaneously (Systematic)

- The cross which was positioned under the conical flask, was not in the same position for each trial (Systematic)

- The conical flask which contained the mixture of reactants was not mixed an equal amount of times in each trial for each different concentration (Systematic)

- Reliability of experiment needs to be improved (Not really an error unless you give a specific example of what caused the unreliability)

- Difficult to determine the exact moment the sulfur precipitate obscured the cross marked on the piece of paper (random)

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No, actually they're not all random. A random error is one where by doing multiple trials and averaging them you should be able to reduce it. A systematic error is something wrong with how you did the experiment.

I'd consider your errors to be:

- Difficult to add the reactants together and start the stopwatch simultaneously (Systematic)

- The cross which was positioned under the conical flask, was not in the same position for each trial (Systematic)

- The conical flask which contained the mixture of reactants was not mixed an equal amount of times in each trial for each different concentration (Systematic)

- Reliability of experiment needs to be improved (Not really an error unless you give a specific example of what caused the unreliability)

- Difficult to determine the exact moment the sulfur precipitate obscured the cross marked on the piece of paper (random)

Hi,

Oh thank you! Your definition of random/systematic errors really cleared things up for me :)

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