MEASUREMENTS. What is the difference between these two measurement rulers? Should we record the same number for each scale reading? The second scale gives.

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Chapter 2 – Scientific Measurement

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Presentation transcript:

MEASUREMENTS

What is the difference between these two measurement rulers? Should we record the same number for each scale reading? The second scale gives us more information, it is more precise.

When writing measurements, we record the digits that we are certain of plus one estimated or uncertain digit. We consider these number significant digits 8.9 cm 8.95 cm

6.00 cm

1120 cm

cm

Significant Digits or Significant Figures We must be aware of the limits of precision for each piece of lab equipment that we use. We must record our data to the proper number of significant figures. You are always allowed one estimated figure in measurements When measured quantities are given to you, it is assumed that the proper number of significant figures were recorded.

Rules for Counting Significant Figures All non-zero digits are significant in _____ 785 m _____ cm ____ Zeros: – Leading Zeros are not significant L _____ 0.5 mL _____ cm _____ – Captive Zeros are significant m _____ L _____ m _____ – Trailing Zeros are significant if there is a decimal point cm _____ 1.30 in _____ L _____ – Trailing Zeros are not significant if there is no decimal point in _____ 800 m _____ mL _____

Determine the amount of significant figures in the following examples: 967 L _____ mL _____ m _____ cm _____ mm _____ m _____ 9.67 L _____ mL _____ m _____

Calculating with Significant Figures Multiply/Divide: The number with the fewest number of sig figs will determine the number of sig figs in the answer. – Example (13.92 g/cm 3 )(23.3 cm 3 ) = g 4 sig figs3 sig figs 324 g

Calculating with Significant Figures Addition/Subtraction: The number with the fewest amount of decimal places determines the amount of decimal places in the answer. – Example 3.76 g g g = g 2 decimal places 20.7 g 2 decimal places 1 decimal places

How many times could you imagine dividing the smallest increment? What length measurement would you record?6.83 cm cm 10 times; each increment being worth 0.01 cm Uncertainty in Measurements Therefore your uncertainty is 0.01 cm. We can express this by writing our measurement as 6.83 cm ± 0.01 cm