The Density of Liquids

Curriculum Big Idea: Chemistry is the study of matter and the changes it undergoes. Big Idea: Chemistry is the study of matter and the changes it undergoes. Concept: The use of significant figures assures that quantitative observations are both accurate and precise. Concept: The use of significant figures assures that quantitative observations are both accurate and precise. PA Standard: Explain the importance of accuracy and precision in making valid measurements. PA Standard: Explain the importance of accuracy and precision in making valid measurements.

Today’s Agenda Opener: Give an example of precise but inaccurate measurements. Opener: Give an example of precise but inaccurate measurements. More with Measurement - Powerpoint More with Measurement - Powerpoint MSE Activity 5: Mass and Volume MSE Activity 5: Mass and Volume (see packet) What Do You Think? Begin Investigate – Measure the mass and volume of water. Discuss how to find its density by graphing the data. Tomorrow – graph the data, and find the density. Closure: What is density? Closure: What is density? Take Home Assignment: Read the Chem Talk on pages , and complete the Checking Up on page 41

Accuracy vs. Precision: Accuracy vs. Precision: Accuracy – THE DISTANCE A Accuracy – THE DISTANCE A MEASUREMENT IS FROM THE ACCEPTED VALUE Precision – THE CONSISTENCY OF A MEASUREMENT Precision – THE CONSISTENCY OF A MEASUREMENT % error: % error: a measure of the % difference between a measured value and the accepted “correct” value formula:| correct – measured | x 100 = % error formula:| correct – measured | x 100 = % errorcorrect

Significant Figures- Certain vs. Uncertain Digits: Certain – DIGITS THAT ARE DETERMINED USING A MARK ON AN INSTRUMENT OR ARE GIVEN BY AN ELECTRONIC INSTRUMENT Certain – DIGITS THAT ARE DETERMINED USING A MARK ON AN INSTRUMENT OR ARE GIVEN BY AN ELECTRONIC INSTRUMENT Uncertain – THE DIGIT THAT IS ESTIMATED WHEN USING AN INSTRUMENT WITH MARKS (ALWAYS A ZERO OR FIVE – FOR THIS CLASS) Uncertain – THE DIGIT THAT IS ESTIMATED WHEN USING AN INSTRUMENT WITH MARKS (ALWAYS A ZERO OR FIVE – FOR THIS CLASS)

Significant Figures- Certain vs. Uncertain Digits: 1. Rules for significant figures (pages 66-67): 1. Rules for significant figures (pages 66-67): a. Nonzero digits b. Initial zeros c. In-between zeros d. Final zeros Example State the number of significant figures in the following set of measurements: Example State the number of significant figures in the following set of measurements: a g b gc kg d. 31,000 mg e cg What statements can you make about the accuracy and precision of measurements a-e? What statements can you make about the accuracy and precision of measurements a-e?

Significant Figures in Calculations A calculated answer cannot be more precise than the least precise measurement from which it was calculated. A calculated answer cannot be more precise than the least precise measurement from which it was calculated. Addition and Subtraction: The answer must be rounded so it has same number of decimal places as the measurement with the least number of decimal places. Addition and Subtraction: The answer must be rounded so it has same number of decimal places as the measurement with the least number of decimal places. Multiplication and Division: The answer must be rounded so that it has the same number of significant figures as the measurement with the least number of significant figures. Multiplication and Division: The answer must be rounded so that it has the same number of significant figures as the measurement with the least number of significant figures. Accuracy and Precision Quick Lab – p. 72 Accuracy and Precision Quick Lab – p. 72

Graphing with Independent and Dependent Variables: independent = X axis (gets changed by scientists during and experiment) independent = X axis (gets changed by scientists during and experiment) dependent = Y axis dependent = Y axis Slope = Y 2 -Y 1 /X 2 -X 1 = Y/ X Slope = Y 2 -Y 1 /X 2 -X 1 = Y/ X Density = mass/volume Density = mass/volume