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Understanding Significant Figures: Rounding and Counting in Data Calculations

Significant figures are crucial in chemistry for indicating the precision of data in calculations. This guide discusses rounding numbers to specific places, such as tenths and thousandths, and illustrates how to count significant figures using the Atlantic/Pacific Rule based on the presence or absence of a decimal point. It explains the importance of significant figures during multiplication/division and addition/subtraction, emphasizing that the answer can only be as precise as the least precise number involved. Practice problems are included for reinforcement.

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Understanding Significant Figures: Rounding and Counting in Data Calculations

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  1. TOPIC: Significant Figures • Do Now: Round9,023.856103 to the… • Tenths • Ones • Hundreds • Thousandths • Thousands

  2. We use significant figures when doing data calculations in chemistry Significant figures are important because they tell us how good the data we are using are.

  3. Counting Significant Figuresusing the Atlantic/Pacific Rule

  4. How to count Significant Figures • Look for a decimal • Decimal point absent = Atlantic Ocean • Decimal point present = Pacific Ocean • Start counting from first non-zero number X   X

  5. 5400 m 2 sig figs has 4 sig figs Decimal point absent: • Start on Atlantic (right) side of # • Start counting with first non-zero digit & count until reach end of # has 5431 m

  6. has 7 sig figs 4 sig figs has 0.004530 km Decimal point present: • Start on Pacific (left) side of # • Start counting with first non-zero digit & count until reach end of # 2545.300 g

  7. Every once in a while: _ 5300 cm A line above a zero means its significant

  8. Let’s practice…get out your packet

  9. Multiplication and Division COUNT SIG FIG for each number Answer can only be as specific as least specific number. Ex: if one number has 3 sig figs and the other has 5 sig figs, you answer can only have 3 sig figs

  10. 24.56 cm x 14 cm = 2 sig figs 4 sig figs 343.84 cm2 343.8 cm2 343 cm2 340 cm2 Answer: 340 ONLY 2 SIG FIGS

  11. Let’s practice…try number 1-3

  12. Addition and Subtraction Underline lowest place value. Answer can only be as specific as the least specific number

  13. Example • 540 + 12.4 + 0.211 + 100 = 652.611 Answer = 700 Hundreds Tens Thousandths Tenths Answer can only be as specific as the least specific number More specific

  14. + 422.63 cm 29.472 cm 115.9 cm hundredths Thousandths Tenths ________________ 568.002 cm 568.00 cm 568.0 cm 568 cm Answer: 568.O Tenths

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