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Significant Figures Chem 140. Why significant figures? Weight of penny: 3 g ± 1 g Not very accurate Weight of truck: 41 057 214 g Also ± 1 g Much more.

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Presentation on theme: "Significant Figures Chem 140. Why significant figures? Weight of penny: 3 g ± 1 g Not very accurate Weight of truck: 41 057 214 g Also ± 1 g Much more."— Presentation transcript:

1 Significant Figures Chem 140

2 Why significant figures? Weight of penny: 3 g ± 1 g Not very accurate Weight of truck: g Also ± 1 g Much more accurate Cardinal Scale Mfg. Co.

3 Why significant figures? Measure of accuracy 3 g Error: 33 % One significant figure

4 Why significant figures? Measure of accuracy 3 g Error: 33 % One significant figure g Error: % Eight significant figures

5 Rules for significant figures 1)Nonzero numbers: Always significant 2)Captive zeroes: Always significant 3)Leading zeroes: Never significant 4)Trailing zeroes: Significant when the decimal point is written

6 Examples 13060

7 Examples four s.f.

8 Examples four s.f

9 Examples four s.f five s.f.

10 Examples four s.f five s.f

11 Examples four s.f five s.f four s.f.

12 Examples four s.f five s.f four s.f × 10 23

13 Examples four s.f five s.f four s.f × four s.f.

14 Multiplying and dividing The number with the fewest s.f. determines how many are in the result.

15 Multiplying and dividing The number with the fewest s.f. determines how many are in the result × (6.022 × ) = × 10 22

16 Multiplying and dividing The number with the fewest s.f. determines how many are in the result × (6.022 × ) = × = 2.6 × 10 22

17 Adding and subtracting Don’t count significant figures, count decimal places.

18 Adding and subtracting Don’t count significant figures, count decimal places =

19 Adding and subtracting Don’t count significant figures, count decimal places =

20 Adding and subtracting Don’t count significant figures, count decimal places =

21 Exact numbers Some numbers have infinite s.f. 60 seconds in a minute 2.54 cm in an inch 2 measurements being averaged


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