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CHM 101/102 CHM 101/102 Laboratory Manual Laboratory Manual Laboratory Manual Significant Figures and Density Significant Figures and Density General Chemistry 101/102 General Chemistry 101/102 Laboratory Manual Laboratory Manual University of North Carolina at University of North Carolina at Wilmington Wilmington

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Page 1: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Significant Figures and DensitySignificant Figures and Density

General Chemistry 101/102General Chemistry 101/102Laboratory ManualLaboratory Manual

University of North Carolina at WilmingtonUniversity of North Carolina at Wilmington

Page 2: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Significant Figures and DensitySignificant Figures and Density

• PurposePurpose To gain an understanding of how to interpret To gain an understanding of how to interpret

uncertainties in laboratory data.uncertainties in laboratory data. To become familiar with the use of common To become familiar with the use of common

laboratory equipment and glassware.laboratory equipment and glassware.

• Safety ConsiderationsSafety Considerations There are no special safety considerations There are no special safety considerations

associated with this laboratory exercise other than associated with this laboratory exercise other than washing your hands before leaving the lab.washing your hands before leaving the lab.

Page 3: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Significant Figures and DensitySignificant Figures and Density

• Accuracy vs. PrecisionAccuracy vs. Precision Accuracy – a statement of how close a measured Accuracy – a statement of how close a measured

value is to the true or accepted value.value is to the true or accepted value. Precision – a statement of how reproducible the Precision – a statement of how reproducible the

measured results are.measured results are.

Page 4: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Significant Figures and DensitySignificant Figures and Density

• Significant FiguresSignificant Figures The value reported for a measurement is rounded The value reported for a measurement is rounded

off so that it contains only the digits known with off so that it contains only the digits known with certainty plus one uncertain one which is the last certainty plus one uncertain one which is the last digit.digit.

• Significant Figure RulesSignificant Figure Rules To determine the number of significant figures in a To determine the number of significant figures in a

reported value, start at the left and count all digits reported value, start at the left and count all digits beginning with the first non-zero digit. beginning with the first non-zero digit.

Examples: 0.003040 => 4 sig. fig.

10,200 => 5 sig. fig.

Page 5: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Significant Figures in CalculationsSignificant Figures in Calculations Addition & Subtraction: The number of decimal Addition & Subtraction: The number of decimal

places in the answer should be equal to the places in the answer should be equal to the number of decimal places in the value with the number of decimal places in the value with the fewest decimal places.fewest decimal places.

Significant Figures and DensitySignificant Figures and Density

Example: 12.0035 g 3.72 g 0.015 g

15.74 g

(4 decimal places)

(2 decimal places)

(3 decimal places)

(2 decimal places)

Page 6: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Significant Figures in CalculationsSignificant Figures in Calculations Multiplication & Division: The number of significant Multiplication & Division: The number of significant

figures in the answer should be the same as the figures in the answer should be the same as the value with the value with the fewest significant figuresfewest significant figures..

Significant Figures and DensitySignificant Figures and Density

Example:

12.36 mL x 1.7 g = 21 gmL4 sig. fig. 2 sig. fig. 2 sig. fig.

Note: Definitions and counted numbers have an Note: Definitions and counted numbers have an unlimited number of significant figures.unlimited number of significant figures.

Page 7: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Procedure – Part 1 a & bProcedure – Part 1 a & b Pour approximately 8 mL of water into a 50 mL Pour approximately 8 mL of water into a 50 mL

graduated cylinder. Record the measured volume graduated cylinder. Record the measured volume to the appropriate number of significant figures. to the appropriate number of significant figures. Repeat the procedure using a 10 mL graduate Repeat the procedure using a 10 mL graduate cylinder.cylinder.

Significant Figures and DensitySignificant Figures and Density

read from the bottom of the meniscus

Page 8: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Procedure – Part 1 c & dProcedure – Part 1 c & d Use a 10 mL graduated pipet to transfer 8 mL of Use a 10 mL graduated pipet to transfer 8 mL of

water to a 50 mL preweighed beaker. Reweigh water to a 50 mL preweighed beaker. Reweigh the beaker and use the mass of water and the the beaker and use the mass of water and the density of water to calculate the volume of water density of water to calculate the volume of water transferred.transferred.

Significant Figures and DensitySignificant Figures and Density

Page 9: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Procedure – Part 2Procedure – Part 2 Determine the identity of an unknown metal by Determine the identity of an unknown metal by

measuring its density (mass/volume). The volume measuring its density (mass/volume). The volume of the metal is determined by “displacement”.of the metal is determined by “displacement”.

Significant Figures and DensitySignificant Figures and Density

Page 10: CHM 101/102 Laboratory Manual Significant Figures and Density General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

• Procedure – Part 2Procedure – Part 2

Significant Figures and DensitySignificant Figures and Density

the difference between these two readings is the volume of the metal