# Safety and Measurement Starting with the basics. Lab Safety  Remember that the lab is a place for serious work!  Careless behavior may endanger yourself.

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Safety and Measurement Starting with the basics

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!

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

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

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

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

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.

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

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?

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

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.

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

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

Unit Prefixes

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

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.

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.

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

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.

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

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.

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

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

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.

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

EQ 7: How do scientists collect and analyze data?

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