The Density of LiquidsThe Density of Liquids

CurriculumCurriculum

Big Idea: Big Idea: Chemistry is the study of Chemistry is the study of matter and the changes it matter and the changes it undergoes.undergoes.

Concept: The use of significant figures Concept: The use of significant figures assures that quantitative observations assures that quantitative observations are both accurate and precise.are both accurate and precise.

PA Standard: Explain the importance of PA Standard: Explain the importance of accuracy and precision in making valid accuracy and precision in making valid measurements. measurements.

Today’s AgendaToday’s Agenda OpenerOpener: Give an example of precise but inaccurate : Give an example of precise but inaccurate

measurements.measurements. More with Measurement - PowerpointMore with Measurement - Powerpoint MSE Activity 5: Mass and VolumeMSE Activity 5: Mass and Volume

(see packet)(see packet)What Do You Think?What Do You Think?Begin Begin InvestigateInvestigate – – MeasureMeasure the mass and volume the mass and volume of water. Discuss how to find its density by of water. Discuss how to find its density by graphinggraphing the data. Tomorrow – graph the data, and the data. Tomorrow – graph the data, and find the density.find the density.

ClosureClosure: What is density?: What is density?Take Home AssignmentTake Home Assignment: : ReadRead the Chem Talk on the Chem Talk on

pages 38-41, and complete the Checking Up on pages 38-41, and complete the Checking Up on page 41page 41

Accuracy vs. Accuracy vs. Precision:Precision:

AccuracyAccuracy – THE DISTANCE A – THE DISTANCE A MEASUREMENT IS FROM THE MEASUREMENT IS FROM THE ACCEPTED VALUEACCEPTED VALUE

PrecisionPrecision – THE CONSISTENCY OF A – THE CONSISTENCY OF A MEASUREMENTMEASUREMENT

% error:% error:a measure of the % difference between a a measure of the % difference between a measured value and the accepted “correct” valuemeasured value and the accepted “correct” value

formula:formula: | | correct – measuredcorrect – measured | x 100 = | x 100 = % error% error

correctcorrect

Significant Figures- Certain vs. Significant Figures- Certain vs. Uncertain Digits:Uncertain Digits:

CertainCertain – DIGITS THAT ARE DETERMINED – DIGITS THAT ARE DETERMINED USING A MARK ON AN INSTRUMENT OR USING A MARK ON AN INSTRUMENT OR ARE GIVEN BY AN ELECTRONIC ARE GIVEN BY AN ELECTRONIC INSTRUMENTINSTRUMENT

UncertainUncertain – THE DIGIT THAT IS – THE DIGIT THAT IS ESTIMATEDESTIMATED WHEN USING AN WHEN USING AN INSTRUMENT WITH MARKS (ALWAYS A INSTRUMENT WITH MARKS (ALWAYS A ZERO OR FIVE – FOR THIS CLASS)ZERO OR FIVE – FOR THIS CLASS)

Significant Figures- Certain vs. Significant Figures- Certain vs. Uncertain Digits:Uncertain Digits:

1. Rules for significant figures (pages 66-67):1. Rules for significant figures (pages 66-67):a. Nonzero digitsa. Nonzero digitsb. Initial zerosb. Initial zerosc. In-between zerosc. In-between zerosd. Final zerosd. Final zeros

Example Example State the number of significant figures in the State the number of significant figures in the following set of measurements: following set of measurements:

a.a. 30.0 g b. 29.9801g30.0 g b. 29.9801g c. 0.03 kg d. 31,000 mgc. 0.03 kg d. 31,000 mg

e.e. 3102. cg3102. cg

What statements can you make about the accuracy and What statements can you make about the accuracy and precision of measurements a-e?precision of measurements a-e?

Significant Figures in Significant Figures in CalculationsCalculations

A calculated answer cannot be more precise A calculated answer cannot be more precise than the least precise measurement from which than the least precise measurement from which it was calculated.it was calculated.

Addition and Subtraction: The answer must be Addition and Subtraction: The answer must be rounded so it has same number of decimal rounded so it has same number of decimal places as the measurement with the least places as the measurement with the least number of decimal places.number of decimal places.

Multiplication and Division: The answer must be Multiplication and Division: The answer must be rounded so that it has the same number of rounded so that it has the same number of significant figures as the measurement with the significant figures as the measurement with the least number of significant figures.least number of significant figures.

Accuracy and Precision Quick Lab – p. 72Accuracy and Precision Quick Lab – p. 72

Graphing with Independent and Graphing with Independent and Dependent Variables:Dependent Variables:

independent = X axis (gets changed independent = X axis (gets changed by scientists during and experiment)by scientists during and experiment)

dependent = Y axisdependent = Y axis Slope = YSlope = Y22-Y-Y11/X/X22-X-X11 = Y/ X = Y/ X Density = mass/volumeDensity = mass/volume