Chemistry Experimental Sources Error
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due to inherent limitations in the measuring equipment, or of the measuring techniques, or perhaps the experience and skill of the experimenter. However mistakes do not count as part of the analysis, though it has to be said that some of possible errors in a lab the accounts given by students dwell too often on mistakes – blunders, let's not be
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coy – and too seldom on the quantitative assessment of error. Perhaps it's easier to do so, but it is not quantitative and sources of error in chemistry titration does not present much of a test of the quality of the results. The development of the skill of error assessment is the purpose of these pages. They are not intended as a course in statistics, so there
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is nothing concerning the analysis of large amounts of data. The Origin Errors – or uncertainties in experimental data – can arise in numerous ways. Their quantitative assessment is necessary since only then can a hypothesis be tested properly. The modern theory of atomic structure is believed because it quantitatively predicted all sorts of atomic properties; yet the experiments used to determine them were inevitably subject to uncertainty, so that there has to be some set sources of error in chemical reaction lab of criteria that can be used to decide whether two compared quantities are the same or not, or whether a particular reading truly belongs to a set of readings. Melting point results from a given set of trials is an example of the latter. Blunders (mistakes). Mistakes (or the much stronger 'blunder') such as, dropping a small amount of solid on the balance pan, are not errors in the sense meant in these pages. Unfortunately many critiques of investigations written by students are fond of quoting blunders as a source of error, probably because they're easy to think of. They are neither quantitative nor helpful; experimental error in the true sense of uncertainty cannot be assessed if the experimenter was simply unskilled. Human error. This is often confused with blunders, but is rather different – though one person's human error is another's blunder, no doubt. Really it hinges on the experimenter doing the experiment truly to the best of his ability, but being let down by inexperience. Such errors lessen with practice. They also do not help in the quantitative assessment of error. An example of this would be transferring solids from the weighing boats to a test tube Only if the human error has a significant impact on the experiment should the student mention it. Instrumental limitations. Uncertainties are inherent in any measuring
We're using the word "wrong" to emphasize a point. All experimental data is imperfect. Scientists know that their results always contain errors. However, one of their goals is to
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minimize errors, and to be aware of what the errors may be. Significant digits
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is one way of keeping track of how much error there is in a measurement. Since they know that all sources of error in marking results contain errors, scientists almost never give definite answers. They are far more likely to say: "it is likely that ..." or "it is probable that ..." than to give an exact answer. http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/experimental_error.html As a science student you too must be careful to learn how good your results are, and to report them in a way that indicates your confidence in your answers. There are two kinds of experimental errors. Random Errors These errors are unpredictable. They are chance variations in the measurements over which you as experimenter have little or no control. There is just as great a chance that http://www.digipac.ca/chemical/sigfigs/experimental_errors.htm the measurement is too big as that it is too small. Since the errors are equally likely to be high as low, averaging a sufficiently large number of results will, in principle, reduce their effect. Systematic Errors These are errors caused by the way in which the experiment was conducted. In other words, they are caused by the design of the system. Systematic errors can not be eliminated by averaging In principle, they can always be eliminated by changing the way in which the experiment was done. In actual fact though, you may not even know that the error exists. Which of the following are characteristics of random errors? Check all that apply. a) doing several trials and finding the average will minimize them b) the observed results will usually be consistently too high, or too low c) proper design of the experiment can eliminate them d) there is no way to know what they are It is not easy to discuss the idea of systematic and random errors without referring to the procedure of an experiment. Here is a procedure for a simple experiment to measure the density of rubbing alcohol (iso-propanol). Materials: digital
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Sponsored links Site friends ChemBuddy ChemFeeds Chemical Forums Chemistry Blog Chem Reddit Chem Dictionary Chemistry Books UC Berkeley's Textbooks Undergraduate: General Chemistry Quantitative Analysis Instrumental Methods Graduate: Reaction Mechanisms Inorganic Chemistry Statistical Mechanics Quantum Mechanics Bonding Theory Coordination Chemistry Organometallic Chemistry Organic Reactions General Interest: Cookie Crumbles Serendipity Chemical Forums > Chemistry Forums for Students > High School Chemistry Forum > CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « previous next » Pages: [1] Go Down Print Author Topic: CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! (Read 21528 times) 0 Members and 1 Guest are viewing this topic. 450sam Very New Member Mole Snacks: +0/-0 Offline Posts: 2 CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « on: May 03, 2009, 07:04:25 AM » We did the basic lab many people do this onewe mix 10 mL of sodium Carbonate with 20 mL of calcium chloridewe filter out the precipitate calcium carbonate using a funnel and filter paper and then measure the mass of the filter paper with the precipitatewhat could be two non-human sources of error and would it make the final concentration too high or too low. how would you improve to minimize this errorhelpp would be GREATLY appreciatedgetting a bit desperate heree!NOT HUMAN ERRORS Logged sjb Global Moderator Sr. Member Mole Snacks: +195/-38 Offline Gender: Posts: 3033 Re: CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « Reply #1 on: May 03, 2009, 07:14:59 AM » How do you define human error? Logged 450sam Very New Member Mole Snacks: +0/-0 Offline Posts: 2 Re: CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « Reply #2 on: May 03, 2009, 07:18:52 AM » human errors assuming u did the experiment perfectly and the errors were caused by the experiment or some could be human errors as long as they are not intentional Logged JimJitsu New Member Mole Snacks: +1/-1 Offline Posts: 4 Re: CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « Reply #3 on: May 03, 2009, 01:26:03 PM » temperature can be one. too cold or too hot can change the reaction rates Logged BeepoGirl Regular Member Mole Snacks: +0/-1 Offline Gender: Posts: 26 Re: CHEMISTRY LAB!!!!!!!! PLEASE HELP NOW! « Reply #4 on: May 04, 2009, 02:17:23 AM »