# Safety and Measurement Starting with the basics. Lab Safety ï‚ Remember that the lab is a...

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Safety and MeasurementStarting with the basics

Lab SafetyRemember 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 DataKey Concept 1 Qualitative data deals with descriptionsKey Concept 2 Quantitative data deals with numbersQualitative:-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. PrecisionKey Concept 3 Accuracy refers to how close a measured value is to an accepted valueKey Concept 4 Precision refers to how close a series of measurements are to one another

Accuracy vs. Precision

Accurate but not precisePrecise but not accurateAccurate and preciseNeither accurate nor precise

ErrorError 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.

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

Percent ErrorA 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 unitsSystme Internationale d'Units (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 unitsLength - meterMass - kilogramTime - secondTemperature kelvinQuantity of matter moleArea m2Derived SI UnitsVolume LDensity g/cm3 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

Unit Prefixes

EQ 4: How are the correct number of significant figures calculated?There are 2 different types of numbersExactMeasuredKC 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 NumbersCounting objects are always exact 2 soccer balls 4 pizzasExact relationships, predefined values, not measured 1 foot = 12 inches 1 meter = 100 cmFor instance is 1 foot = 12.000000000001 inches? No 1 ft is EXACTLY 12 inches.

Measured NumbersDo you see why Measured Numbers have erroryou 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 NumbersKC 3: When recording measurements, record all known values then best guess

Significant Figures RulesRule 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 FiguresKC 4: Everything is significant except zeroes, sometimes

Significant FiguresKC 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 PracticeHow many significant figures are in the following numbers?.0030510120.000061.03.5x1046.02x1023

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

Scientific Notation5.67 x 105 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 NotationThe number of places moved equals the value of the exponentThe exponent is positive when the decimal moves to the left and negative when the decimal moves to the right.800 = 8.0 x 1020.0000343 = 3.43 x 105

EQ 7: How do scientists collect and analyze data?