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# Chemistry - Significant Digits

## on Sep 23, 2010

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## Chemistry - Significant DigitsPresentation Transcript

•
• Sample Question 1
• Which is the most appropriate unit in which to measure the length of the McDevitt hallway?
• a. millimeters b. grams
• c. meters d. kilometers
• Sample Question 2
• There are 1,000 _____ in one liter?
• a. milliliters b. centiliters
• c. kiloliters d. SI liters
View slide
• Measurements View slide
• Making Measurements
• Always estimate the final digit.
• Making Measurements
• What’s the difference?
• Accuracy vs. Precision
• Precision = how close your measurements are to each other
• Accuracy = how close your measurements are to the actual value
• Sig. Figs.
• In Math…
• What’s the difference between:
• 5.6,
• 5.60, and
• 5.600?
• Significant Figures
• All precisely-known digits, plus the final, estimated digit of a measurement.
• Significant Figures
• Include:
• Any non-zero digit.
• Zeroes that aren’t placeholders.
• Zeroes between other significant digits.
• Placeholder…?
• To find out if the zero is a placeholder… REMOVE IT and see if the number is MATHEMATICALLY equal!
• If it is not, the zero is a placeholder!
• Which are significant?
• 53 km
• 2003 g
• 30.000 mL
• 919.1984 m
• 204.6 kg
• 10,000,000,000 L
• 7080 mg
• 77.01 mL
• Which are significant?
• 80 mL
• 700,560 g
• 45.05 cm
• 62.000 L
• 9,490.50 g
• 80,000.1 mg
• 78.10 kL
• 69.000003003 L
• Infinite Sig. Figs.
• Exact, counted numbers
• Example: “There are 28 students in the class.”
• (Would not make sense to say that there are 28.00 students)
• Working with Sig. Figs.
• ROUNDING!
• Find the quantity with the smallest number of decimal places .
• Keep the number of decimal places you found above.
• Example
• 17.85 g + 24.6105 g
• 17.85 – 2 decimal places
• 24.6105 – 4 decimal places
• 17.85
• + 24.6105
• 42.4605
• Should have TWO decimal places.
• 42.46 g
• Try These
• 17.0 – 15.45 =
• 65 + 21.0004 =
• 107.22 – 45.23 =
• 1.6
• 86
• 61.99
• Multiplying and Dividing
• Find the quantity with the smallest number of significant digits .
• Multiply/Divide.
• Keep the number of SIGNIFICANT DIGITS you found above.
• Example
• 7.800 m x 24.600 m
• 7.800 – 4 significant digits
• 24.600 – 5 significant digits
• 7.800
• x 24.600
• 191.880000
• Should have FOUR significant digits.
• 191.9
• Try These
• 7.888 x 45.01 =
• 4.010 x 30.1 =
• 1984 / 9.19