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Safety and Measurement Starting with the basics

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Lab Safety Remember that the lab is a place for serious work! Careless behavior may endanger yourself and others and will not be tolerated! Remember that the lab is a place for serious work! Careless behavior may endanger yourself and others and will not be tolerated!

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Essential Question 1: What is the difference between precision and accuracy with respect to experimental data? KnowWant to knowLearned

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Types of Experimental Data Key Concept 1 – Qualitative data deals with descriptions Key Concept 2 – Quantitative data deals with numbers Key Concept 1 – Qualitative data deals with descriptions Key Concept 2 – Quantitative data deals with numbers Qualitative: -the frame is yellow -the frame looks old -the inside looks reflective Quantitative: -the frame measures 4” x 6” -the frame weighs 3lbs -the frame costs $15

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Accuracy vs. Precision Key Concept 3 – Accuracy refers to how close a measured value is to an accepted value Key Concept 4 – Precision refers to how close a series of measurements are to one another Key Concept 3 – Accuracy refers to how close a measured value is to an accepted value Key Concept 4 – Precision refers to how close a series of measurements are to one another

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Accuracy vs. Precision Accurate but not precisePrecise but not accurate Accurate and preciseNeither accurate nor precise

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Error Error is defined as the difference between the experimental value and an accepted value. The error equation is: error = experimental value – accepted value. Percent error expresses error as a percentage of the accepted value. Error is defined as the difference between the experimental value and an accepted value. The error equation is: error = experimental value – accepted value. Percent error expresses error as a percentage of the accepted value.

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Error KC 5: Experimental value is what you get from actually doing the measurement or experiment KC 6: Accepted (actual) value is the constant value from a textbook or other resource KC 5: Experimental value is what you get from actually doing the measurement or experiment KC 6: Accepted (actual) value is the constant value from a textbook or other resource

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Percent Error A substance has an accepted density of 2.00 g/L. You measured the density as 1.80 g/L. What is the percent error?

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Essential Question 2: What are the appropriate SI units for length, mass, time, temperature, quantity of matter, area, volume, and density? KnowWant to knowLearned

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SI units Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. Key Concept 1: base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units. Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. Key Concept 1: base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.

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SI units Length - meter Mass - kilogram Time - second Temperature – kelvin Quantity of matter – mole Area – m 2 Length - meter Mass - kilogram Time - second Temperature – kelvin Quantity of matter – mole Area – m 2 Derived SI Units Volume – L Density – g/cm 3 or g/mL Key Concept 2: These are the SI units for the following base

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EQ 3: What are the relationships among SI unit prefixes (centi-, milli-, kilo-)? KnowWant to knowLearned

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Unit Prefixes

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EQ 4: How are the correct number of significant figures calculated? There are 2 different types of numbers Exact Measured KC 1: Exact numbers are obtained when you count objects or use a defined relationship. KC 2: Measured numbers are measured with a measuring device so these numbers have ERROR There are 2 different types of numbers Exact Measured KC 1: Exact numbers are obtained when you count objects or use a defined relationship. KC 2: Measured numbers are measured with a measuring device so these numbers have ERROR

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Exact Numbers Counting objects are always exact 2 soccer balls 4 pizzas Exact relationships, predefined values, not measured 1 foot = 12 inches 1 meter = 100 cm For instance is 1 foot = 12.000000000001 inches? No 1 ft is EXACTLY 12 inches. Counting objects are always exact 2 soccer balls 4 pizzas Exact relationships, predefined values, not measured 1 foot = 12 inches 1 meter = 100 cm For instance is 1 foot = 12.000000000001 inches? No 1 ft is EXACTLY 12 inches.

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Measured Numbers Do you see why Measured Numbers have error…you have to make that guess! All but one of the significant figures are known with certainty. The last significant figure is only the best possible estimate. To indicate the precision of a measurement, the value recorded should use all the digits known with certainty. Do you see why Measured Numbers have error…you have to make that guess! All but one of the significant figures are known with certainty. The last significant figure is only the best possible estimate. To indicate the precision of a measurement, the value recorded should use all the digits known with certainty.

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Measured Numbers KC 3: When recording measurements, record all known values then best guess

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Significant Figures Rules Rule 1: Nonzero numbers are always significant. Rule 2: Zeros between nonzero numbers are always significant. Rule 3: All final zeros to the right of the decimal are significant. Rule 4: Placeholder zeros are not significant. To remove placeholder zeros, rewrite the number in scientific notation. Rule 5: Counting numbers and defined constants have an infinite number of significant figures. Rule 1: Nonzero numbers are always significant. Rule 2: Zeros between nonzero numbers are always significant. Rule 3: All final zeros to the right of the decimal are significant. Rule 4: Placeholder zeros are not significant. To remove placeholder zeros, rewrite the number in scientific notation. Rule 5: Counting numbers and defined constants have an infinite number of significant figures.

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Significant Figures KC 4: Everything is significant except zeroes, sometimes

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Significant Figures KC 5: When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement. KC 6: When measurements are multiplied or divided, the answer can contain no more significant figures than the least accurate measurement. KC 5: When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement. KC 6: When measurements are multiplied or divided, the answer can contain no more significant figures than the least accurate measurement.

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Significant Figures Practice How many significant figures are in the following numbers? .00305 10 120.00006 1.0 3.5x10 4 6.02x10 23 How many significant figures are in the following numbers? .00305 10 120.00006 1.0 3.5x10 4 6.02x10 23

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EQ 6: How do scientists record very large or very small quantities? KC 1: Scientific notation can be used to express any number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent). Count the number of places the decimal point must be moved to give a coefficient between 1 and 10 KC 1: Scientific notation can be used to express any number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent). Count the number of places the decimal point must be moved to give a coefficient between 1 and 10

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Scientific Notation 5.67 x 10 5 coefficient base exponent In order for a number to be in correct scientific notation, the following conditions must be true: KC 2: The coefficient must be greater than or equal to 1 and less than 10. KC 3: The base must be 10. KC 4: The exponent must show the number of decimal places that the decimal needs to be moved to change the number to standard notation. 5.67 x 10 5 coefficient base exponent In order for a number to be in correct scientific notation, the following conditions must be true: KC 2: The coefficient must be greater than or equal to 1 and less than 10. KC 3: The base must be 10. KC 4: The exponent must show the number of decimal places that the decimal needs to be moved to change the number to standard notation.

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Scientific Notation The number of places moved equals the value of the exponent The exponent is positive when the decimal moves to the left and negative when the decimal moves to the right. 800 = 8.0 x 10 2 0.0000343 = 3.43 x 10 –5 The number of places moved equals the value of the exponent The exponent is positive when the decimal moves to the left and negative when the decimal moves to the right. 800 = 8.0 x 10 2 0.0000343 = 3.43 x 10 –5

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EQ 7: How do scientists collect and analyze data?

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