Download presentation
Presentation is loading. Please wait.
Published byDrusilla Lucas Modified over 9 years ago
1
1 § 02-03 Using Scientific Measurements A. Accuracy and Precision
2
2 Accuracy: = closeness of measurements to the correct or accepted value of the quantity measured. Precision: = closeness of a set of measurements of the same quantity made in the same way. A. Accuracy and Precision
3
3 Precision: = closeness of a set of measurements of the same quantity made in the same way. A. Accuracy and Precision
4
4 HIGHLOW Accuracy:Precision:
5
5 LOWHIGH
6
6 Accuracy:Precision: LOW
7
7 HIGH
8
8 Age (yrs) of Students in CHEM 320 Class AClass BClass C 17.025.04.5 15.410.24.3 15.822.14.2 16.212.14.3 15.910.35.3
9
9 § 02-03 Using Scientific Measurements B. Percent Error
10
10 To give meaning to experimental data, it is often helpful to compare them with the ‘correct’ or accepted values by calculating the PERCENT ERROR. B. Percent Error
11
11 Calculate by: (p. 45) B. Percent Error
12
12 Example: A student measures the mass of an object to be 24.21 g and its volume to be 11.32 mL. The known density of the substance is 2.00 g/mL. What is percent error of the student’s measurement?
13
13 Example: A student measures the mass of an object to be 24.21 g and its volume to be 11.32 mL. The known density of the substance is 2.00 g/mL. What is percent error of the student’s measurement?
14
14 density = 24.21 g and its volume to be 11.32 mL. = -7 %
15
15 There is always some error in measurement - even w/ the best technical skill and instruments. General rule of thumb: report to most digits of instrument (and if between, add 1/2 of a unit - e.g., see p. 46 of book) C. Error in Measurement
16
16 The length of the nail is definitely between 6.3 cm and 6.4 cm. Because it is about half-way between, it should be read as 6.35 cm, with the understanding that the hundredths place is somewhat uncertain.
17
17 In science, the certainty of the data is very important. This is inherent in the number of displayed SIGNFICANT FIGURES. D. Significant Figures
18
18 In a measurement, the digits known with certainty plus one final digit (which may be known with certainty or estimated) are the significant figures. D. Significant Figures
19
19 Significant figures don’t necessarily mean certain, they mean scientifically significant. D. Significant Figures
20
20 As a chemistry student, you will need to use and recognize figures when you work with measured quantities and report your results, or evaluate others’. There are definite rules of significant figures... (q.v. Table 2-5 - know by usage) D. Significant Figures
21
21 As a chemistry student, you will need to use and recognize figures when you work with measured quantities and report your results, or evaluate others’. There are definite rules of significant figures... (q.v. Table 2-5 - know by usage)
22
22 How many significant figures are there in each of the following measurements? 40.5 87 009 0.01 5 280 100.01 sig. fig.=3(rule 1) =5(rule 1) =1(rule 2) =3(rule 2) =5(rule 3)
23
23 2 000 may contain one or four significant figures (depending on how many zeros are place holders). FOR MEASUREMENTS IN THIS BOOK, ASSUME THAT 2 000 HAS ONE SIGNFICANT FIGURE. TO EMPHASIZE THAT IT HAS FOUR S.F., WRITE: 2 000. (N.B. decimal point). {2 000.0 has 5 s.f.}
24
24 Read book - if you have any questions, ask Dr. Fisher. But this material should have been covered many times in previous classes. E. Rounding
25
25 For multiplication and division, the number of significant figures in the answer can have NO MORE than the fewest number of significant figures in any of the measurements... (e.g... F. Multiplication & Division of Significant Figures
26
26 The fewest significant figures in the measurements is three (3.43 g) - so that’s the what that the answer will have.
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.