Significant Figures Computer usage and calculations in analytical

Significant Figures Computer usage and calculations in analytical chemistry

Significant Figures 1. 0 x 101 and 1. 000 x 101 are they same? • Uncertainities in measurements • Significant figures: all precise digits + first uncertain digit • Shows how precise a measurement

Rules • Non-zero digits are significant. 213. 45 → Five significant figures • Zeros in between non-zeros are significant 170005. 002 → Nine significant figures • Leading zeros are NOT significant. 0. 0021 → Two significant figures • Trailing zeros • If it is a decimal then significant. 0. 1000 → Four significant figures • No decimal: Not clear. It must be shown by a special notation. The best way to do it is a scientific notation Trailing zeros are not clear in 730000. If we state this number as 7. 300 x 10 5 depending on the quality of measurement, then the first four number s will ve significant while last two trailing zeros are not significant.

Significant Figures 200 One significant figure 200. 2. 00 x 102 Three significant figures 0. 01000 kg Three significant figures 200. 001 Six significant figures → 10. 00 g Four significant figures How many significant figures are there in 20. 00?

Significant Figures in Addition/Subtraction • Count decimal places. Results can only be as precise as the least precise number processed 7. 3 – 2. 19 = 5. 11 = 5. 1 1322. 42 + 0. 1176 = 1322. 5376 = 1322. 54 What is total amount of Na. OH if 1. 27 kg Na. OH is added onto 312 kg Na. OH? 312 + 1. 27 = 313. 27 or 313? For this Na. OH we don’t have any idea about subkg level, so we cannot report the results of addition as 313. 27. Reporting as 313. 27 means that the total amount as precise as. 27 level however it is not.

Significant Figures in Multiplying/Dividing • Results can have as many significant figures as the smallest significant figures processed. 4 x 2. 0000 = 8 5. 2 x 2. 5 = 13 Calculate the area of rectangular with dimensions of 2. 32 m and 0. 92 m A= a. b = 2. 32 x 0. 92 = 2. 1344 m 2 = 2. 1 m 2 PS: Rounding in calculations must be done at the end of the processes not in the intermediate steps.

Significant figures How many significant figures are there in the following numbers? 13. 423 150. 520 0. 0771 0, 004400 Solve the following problems. 2, 1 + 0, 043 + 6, 21 = 27, 42 x 42, 241 = REFERENCES Skoog DA, West DM, Holler FJ, Crouch SR; Fundementals of nalytical Chemistry, 9 th ed, Brooks Cole Cengage Learning, 2014. Schwartz LN; Journal of Chemical Education, 1985, 62, 693.