Significant Figures Chem 140. Why significant figures? Weight of penny: 3 g ± 1 g Not very accurate...
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Transcript of Significant Figures Chem 140. Why significant figures? Weight of penny: 3 g ± 1 g Not very accurate...
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 accurate
Cardinal Scale Mfg. Co. Cardinal Scale Mfg. Co.
Cardinal Scale Mfg. Co.
Why significant figures? Measure of accuracy 3 g
Error: 33 % One significant figure
Why significant figures? Measure of accuracy 3 g
Error: 33 % One significant figure
41 057 214 g Error: 0.0000024 % Eight significant figures
Rules for significant figures
1) Nonzero numbers: Always significant
2) Captive zeroes: Always significant3) Leading zeroes: Never significant4) Trailing zeroes: Significant when
the decimal point is written
Examples
13060
Examples
13060 four s.f.
Examples
13060 four s.f.13060.
Examples
13060 four s.f.13060. five s.f.
Examples
13060 four s.f.13060. five s.f.
0.001040
Examples
13060 four s.f.13060. five s.f.
0.001040 four s.f.
Examples
13060 four s.f.13060. five s.f.
0.001040 four s.f.
6.022 × 1023
Examples
13060 four s.f.13060. five s.f.
0.001040 four s.f.
6.022 × 1023 four s.f.
Multiplying and dividing The number with the fewest s.f.
determines how many are in the result.
Multiplying and dividing The number with the fewest s.f.
determines how many are in the result. 0.043 × (6.022 × 1023) = 2.58946 ×
1022
Multiplying and dividing The number with the fewest s.f.
determines how many are in the result. 0.043 × (6.022 × 1023) = 2.58946 ×
1022
= 2.6 × 1022
Adding and subtracting Don’t count significant figures,
count decimal places.
Adding and subtracting Don’t count significant figures,
count decimal places. 3.54 + 0.0152 = 3.5552
Adding and subtracting Don’t count significant figures,
count decimal places. 3.54 + 0.0152 = 3.5552
Adding and subtracting Don’t count significant figures,
count decimal places. 3.54 + 0.0152 = 3.5552 3.56
Exact numbers Some numbers have infinite s.f.
60 seconds in a minute 2.54 cm in an inch 2 measurements being averaged