Examples of Accuracy and Precision in Chemistry
The importance of accuracy and precision in chemistry is necessary to overcome errors in result and match the required set of parameters and standards.
To match these conditionalty’s one has to go through the entire analytical process and follow appropriate validation, suitable calibration leading to results that are traceable to International standards.
For a chemical analyst, accuracy becomes a reliable tool to cross check if the intended standards are matched with or not.
Measurements affect the daily lives of everyone and so we need to have sound accurate and reliable measurements which are essential to the function of modern society.
The role of chemical analysts remained same over the years but the instruments of measurements have changed over the years and have made the accuracy and precision in chemical analysis more potent.
For example when it was de-coded that carrots can help in preventing night blindness, it was an chemical analyst who segregated the various chemical components of carrot and identified the exact active component as beta-carotene and this could be exemplified with only accuracy and precision analysis of how much a person needs this yellow pigment per day to help prevent the blindness.
The issue of accuracy and precision sometimes leads to interesting and some dramatic consequences.
The quality of the balance we use to measure mass is important in a measurement and when speak about high quality measurement, what exactly we meant by that?
For chemist Faisclough- Baity, these two terms mean completely different things and for him accuracy relates to how close a measurement is to its true value while precision relates to how close repeated measurements are to each other whether they are accurate or not!
A set of measurements could be accurate or could be precise and sometimes can show both the characteristics and in some rare cases won’t show any of these.
But instruments fine tuned would definitely yield measurements that are both accurate and precise.
Let us now find out why it is important for us to know uncertainties in our measurements and to worry about precision and accuracy?
In most of the cases our lives, huge cash or our jobs could be at risk if we fail to do a proper measurements fo these and don’t know what we want these to do?
Similarly the dosage of drugs must be measured with utmost care and within known limits to avoid doing harm to us instead of drugs giving good result.
The amount of fuel loaded in a fighter aircraft is very critical as it has to go for specified sorties and return within a specified time frame and that calls for a very very precise measurement of the sorties and also impending enemy engagement in air.
The impure water that we intake could put all our lives in risk and so a accurate measurement is made to find the amount of bacteria and harmful planktons before a even more precise amount of anti bacteria treatment is carried out before released for human consumption.
The dosage of anesthesia given to a patient undergoing a general anethesia surgery is again speaks a volume of how accuracy and precision takes into account for our safety.
The amount of anesthesia required, the duration of surgery, the body weight, the blood – body weight ratio and blood type are all taken into account.
To assess the precision and accuracy of a different values the calculations must contain at least as much uncertainty as is present in the measured values we use to obtain these results and this means that when perform calculations we may not accept all of the digits appearing in calculator display as that definitely would make the calculations very clumsy and huge, but we do make arrangements to make these simpler on us.
The advent of significant numbers is one such action we undertake to make our calculations friendlier and closer to accuracy and more than most occasions we have a precise reading.
Examples of accuracy and precision may include the utilisation of this technique in forensic analysis which might be utilised for a speedy conviction of a guilty and or error leading into a situation where a guilty goes scot-free.
> In commerce the technique is used to match and set standards for different commercial goods to prevent sub-standards supply and also high cost involved in replacement and eventual loss to customers.
> This technique is used for better distribution of potable water and also used for detection of contaminants.
> Incorrect medication due to less precise formulation could lead to disaster and so this technique is utilised for better combination of active ingredients in a tablet.
> The changes in soil profile and analysis of this help us change the pH at right moment before a particular crop is cultivated.
> The pH of water is balanced with precise inputs from a chemical analyst to start any kind of pisci-culture practice.
> Geographical areas with less or no active salts like iodine can lead to health hazards like hyper and hypo thyroid diseases and to prevent such things we again need accurate and precise readings to identify the areas.
> We need precise and accurate readings of the collected samples to identify and help prevent the spread of vector borne killer diseases.
> The geographical areas with arsenic level higher in water needs these accurate and precise inputs to not only identify but also prescribe a proper dosage of anti-arsenic chemicals.
For any kind of analysis, the implications have to be taken care of before devising a sampling method and that leads a long way in getting the right amount and correct result.
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Answers:Example 1: A dart board
Accuracy: i get most of my darts around the centre. Not necessarily close together.
Precision: all my throws land in the exact same area (whether or not it is close to the centre)
Example 2: Packets of Lollies
The maufacturer claims each pack contains 20 lollies
Accuracy: a sample of packets have 19,20,22,18,21,19,21 lollies. The average is 20. Accurate to the claim.
Precision: a sample of packets have 18,17,17,17,18,18,17 lollies. Not accurate to the claim, but the values are constant.
Example 3: An experimental result in a chemistry lab
Doing an experiment, with five trials, the end results of the five trials for whatever is being tested are:
35kg 36kg 33kg 35kg 36kg
The actual value (as found in a scientific data book) is meant to be 42kg.
From the results, the average value is 35kg. This is not at all accurate since the actual value should be 42kg. The results are precise however, since they do not vary from each other.
Question:We are doing a lab where we take an object and measure it with 5 scales. For example, weighing an eraser with 5 beam balances. We are trying to find uncertainty. All the answers we get are very close to each other with a difference of .1 or .2 Are we measuring precision or accuracy?
Answers:Precision concerns how closely bunched your results are. If they are closely bunched then they are precise. If they are widely spread then they are imprecise.
Accuracy concerns how close your average value is to the true value. If your average is close to the true value then your results are accurate. If your average is far from the true value then your results are inaccurate.
You say your results are very close to each other - this suggests they are precise. Whether they are accurate depends on whether the eraser actually weighs close to your mean answer. The fact that your results are precise suggests good experimental technique and your data is also likely to be accurate. It could however be precise and inaccurate if there is a source of systematic error.
Question:Please dont just define then, I want to understand teh diffrence
THANK YOU!!! Lol its kinda hard understanding a dart board can you use a ruler and a caliper instead?
Answers:Precision is the ability to reproduce the result. Accuracy is having the "correct" answer. For example, if you throw five darts and they all miss the board by many feet, but all land in the same spot (say, all in same part of the floor), then the darts are precise, but not accurate. If you throw the darts and they all land on different parts of the board, but not all together, they are fairly accurate, but not precise. Precision is about getting the same result each time, regardless of how right the answer is. Accuracy is getting values close to the accepted value (the correct value), but does not require each answer to be close to one another. In chemistry, being accurate is not enough. Results must be repeatable, must be precise, in order to prove that a pattern exists. Getting the right answer once does not prove a concept.
Question:Example: the density of copper is listed as 8.94 g/cm3. two students each make three density determinations of samples of the substance. student a's results are 7.3, 9.4, and 8.0 and student b's results are 8.4, 8.8, and 8.0. compare the two sets of results in terms of precision and accuracy
Answers:-precision is how close the values are to each other, which is expressed by standard deviation
-accuracy is how close the values are to the accual value, whick is expressed by percent error
Chemistry: Precision and Accuracy :www.mindbites.com In this lesson, Prof. Yee discusses precision and accuracy in measurements. He explains that all measurements will have a degree of uncertainty due to instrumentation, and the range of uncertainty will appear in the last digit of the measurement. You want to have measurements that are both precise and accurate. Precision is the reproducibility of the measurement of a quantity and is tied to the concept of random error. Prof. Yee uses a ruler as an example of precision. Accuracy refers to how close a measurement is to a hypothetical true value. It is possible for a measurement to be precise but not accurate if there is a systematic error. Systematic error is an error inherent to the measurement of a value, such as a clock that is consistently 5 minutes fast. Finally, Prof. Yee explains the relationship between precision and accuracy using a game of darts. Taught by Professor Yee, this lesson was selected from a broader, comprehensive course, Chemistry. This course and others are available from Thinkwell, Inc. The full course can be found at www.thinkwell.com The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals ...
Accuracy & Precision :This is a video we created for Chemistry class describing what accuracy and precision are. Not too much effort was put into it due to the fact that it was for school.