Accuracy and Precision in the Lab Precision and
![Accuracy and Precision in the Lab Accuracy and Precision in the Lab](https://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-1.jpg)
Accuracy and Precision in the Lab
![Precision and Accuracy Errors in Scientific Measurements Precision - Refers to reproducibility or “How Precision and Accuracy Errors in Scientific Measurements Precision - Refers to reproducibility or “How](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-2.jpg)
Precision and Accuracy Errors in Scientific Measurements Precision - Refers to reproducibility or “How close the measurements are to each other. ” Accuracy - Refers to how close a measurement is to the real or true value. Systematic error - produces values that are either all higher or all lower than the actual value. Random Error - in the absence of systematic error, produces some values that are higher and some that are lower than the actual value.
![Good accuracy Good precision Good accuracy Poor precision Poor accuracy Good precision Poor accuracy Good accuracy Good precision Good accuracy Poor precision Poor accuracy Good precision Poor accuracy](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-3.jpg)
Good accuracy Good precision Good accuracy Poor precision Poor accuracy Good precision Poor accuracy Poor precision
![Balances 0. 1 mg precision Accuracy determined by calibration Balances 0. 1 mg precision Accuracy determined by calibration](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-4.jpg)
Balances 0. 1 mg precision Accuracy determined by calibration
![Graduated Cylinder Estimate the volume in the graduated cylinder… Most would read between 19. Graduated Cylinder Estimate the volume in the graduated cylinder… Most would read between 19.](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-5.jpg)
Graduated Cylinder Estimate the volume in the graduated cylinder… Most would read between 19. 1 to 19. 3 m. L No one would properly read the volume as high as 19. 5 m. L or as low as 19. 0 m. L. No one could reasonably read the volume to the 1/100 s digit. Correct way to read a graduated cylinder
![Graduated Cylinder Incorrect way to read a graduated cylinder Graduated Cylinder Incorrect way to read a graduated cylinder](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-6.jpg)
Graduated Cylinder Incorrect way to read a graduated cylinder
![Burette Burette](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-7.jpg)
Burette
![Spectronic-20 Estimate the reading on the upper scale… Most would read between 35. 4 Spectronic-20 Estimate the reading on the upper scale… Most would read between 35. 4](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-8.jpg)
Spectronic-20 Estimate the reading on the upper scale… Most would read between 35. 4 to 35. 6 %T No one would properly read the scale as high as 36. 0 or as low as 35 %T.
![The Number of Significant Figures in a Measurement Depends Upon the Measuring Device A The Number of Significant Figures in a Measurement Depends Upon the Measuring Device A](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-9.jpg)
The Number of Significant Figures in a Measurement Depends Upon the Measuring Device A linearly calibrated instrument can usually be read to 1 digit more precision than the engraved calibration
![Significant Digit Rules and Conventions A significant figure (also called a significant digit) in Significant Digit Rules and Conventions A significant figure (also called a significant digit) in](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-10.jpg)
Significant Digit Rules and Conventions A significant figure (also called a significant digit) in a measurement is one which is known to some level of precision. The rules presented here are simplifications of a more complete statistical analysis and should be used to imply a certain confidence in a written numerical value. These rules are not infallible. To avoid round-off errors when making multiple-step calculations, carry one or two extra significant figures in the intermediate calculations. Round off the answer to the appropriate number of significant figures at the very end.
![Rules: All nonzero digits in a reported value are significant. 422 g has 3 Rules: All nonzero digits in a reported value are significant. 422 g has 3](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-11.jpg)
Rules: All nonzero digits in a reported value are significant. 422 g has 3 significant figures (SFs) Zeroes between nonzero digits are significant. 2003 miles has 4 SFs Trailing zeroes after the decimal point are significant. -2. 10 J has 3 SFs 0. 110 g has 3 SFs Leading zeroes after the decimal point are not significant. 0. 00214 g has 3 SFs Trailing zeroes in a number without a decimal point lead to ambiguity and are usually assumed not to be significant. Eliminate the ambiguity by converting to scientific notation (exponential notation). 96, 500 C (3, 4, or 5 SFs) might be 9. 650 x 104 C (4 SFs)
![Handling Significant Figure in Calculations Addition/Subtraction: The number of decimal digits in the final Handling Significant Figure in Calculations Addition/Subtraction: The number of decimal digits in the final](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-12.jpg)
Handling Significant Figure in Calculations Addition/Subtraction: The number of decimal digits in the final answer is the same as the minimum number of decimal digits in any measurement. +
![Multiplication/Division: The total number of significant figures in the final answer is equal to Multiplication/Division: The total number of significant figures in the final answer is equal to](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-13.jpg)
Multiplication/Division: The total number of significant figures in the final answer is equal to the minimum number of significant figures in any measurement. Area = Length x Width Length = 12. 5 cm Width = 2. 0 cm X
![Logarithms: The number of decimal digits in the answer is equal to the number Logarithms: The number of decimal digits in the answer is equal to the number](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-14.jpg)
Logarithms: The number of decimal digits in the answer is equal to the number of significant digits in the measurement. Log 54 (2 SFs) = 1. 73 (2 decimal digits) Powers of 10 and antilog: The number of significant figures in the answer is equal to the number of decimal digits in the measurement. 10 -2. 53 (2 decimal digits) = 0. 0030 (2 SFs)
![Review • Precision refers to the reproducibility of multiple measurements • Accuracy refers to Review • Precision refers to the reproducibility of multiple measurements • Accuracy refers to](http://slidetodoc.com/presentation_image_h/15ed81c6931b5173e5759b00b11c3c2b/image-15.jpg)
Review • Precision refers to the reproducibility of multiple measurements • Accuracy refers to how close a measurement or average of measurements is to the real or true value. • Errors can be systematic (unidirectional and can be eliminated) or random (bidirectional and normal) • A linearly calibrated instrument can usually be read to 1 digit more precision than the engraved calibration • Presenting measurements and calculated results with appropriate significant digits is a way to display the estimated precision of the values. • The rules of significant figure calculations are merely approximations of a much more rigorous statistical analysis and must be used carefully to avoid introducing unexpected and possibly undetected errors.
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