Scientific Measurements Chapter 3

Objectives Construct and use tables and graphs to interpret data sets. Solve simple algebraic expressions. Measure with accuracy and precision (length, volume, mass, temperature, time, etc.) Convert within a unit (such as, centimeters to meters). Use common prefixes such as milli-, centi-, and kilo-. Use scientific notation, where appropriate. Use ratio and proportion in the solution of problems.

Objectives Determine the correct number of significant figures. Determine percent error from experimental and accepted values. Use appropriate metric/standard international (SI) units of measurement for mass (kg); length (m); and time (s). Use Celsius and Kelvin scales.

Observations Qualitative: results in descriptions (Canadian geese) Quantitative: results in numerical form (15 Canadian geese)

Accuracy and Precision Accuracy: how close measurement is to true value Precision: how close several measurements are to the same value The number of digits in a measurement

Study Buddy Review How would you describe the following sets of numbers? 68.6, 68.7, 68.9 Goal = , 40.01, Goal = , 6.0, 7.0 Goal = , 0.87, Goal= 0.87

Study Buddy Review How would you describe the following sets of numbers? 68.6, 68.7, 68.9 Goal = 23.0 –Precise but inaccurate 40.02, 40.01, Goal = –Precise and accurate 2.4, 6.0, 7.0 Goal = 4.0 –Imprecise and inaccurate 0.874, 0.87, Goal= 0.87 –Imprecise but accurate

Percent Error Error: difference between experimental value and accepted value Accepted value: true or correct value from literature Experimental value: measured value determined from lab % error = accepted value –experimental value x 100 accepted value

Study Buddy Review Convert the following to scientific notation: g 10,000 m Convert the following to standard notation: 1.5 x dL 2.2 x 10 5 mL

Study Buddy Review Convert the following to scientific notation: g5 x g 10,000 m1 x 10 4 m Convert the following to standard notation: 1.5 x dL dL 2.2 x 10 5 mL220,000 mL

The Metric System

Metric and SI units Metric System used in science SI System – International System of units based on metric system –Used to standardize quantities between scientists

Common Units in Chemistry Quantity it represents SI unitCommon metric unit in Chemistry Lengthmeter (m)centimeter (cm) Masskilogram (kg)gram (g) Volumem 3 (cubic meters) milliliter (mL) Temperature Kelvin (K)Celsius ( o C)

Mass A measure of the quantity of matter; amount of material in an object Never changes (Weight – force due to the pull of gravity on an object)

Volume Cube Demo Cube is 10 cm x 10 cm x 10 cm = 1000 cm 3 (also 1 dm x 1 dm x 1 dm or 1 dm 3 ) Cube is filled by water in filled 1 liter beaker so 1 L = 1000 cm 3 1 L = 1000 mL= 1000 cm 3 = 1 dm 3 *IMPORTANT RELATIONSHIP: 1 cm 3 = 1 mL

Temperature Temperature: a measure of the average kinetic energy of particles that make up substance Use Celsius or Kelvin temperature in chemistry Kelvin Temperature scale based on absolute zero Absolute zero or 0 K –coldest possible temperature –Temperature where motion of particles stops A degree in Kelvin is equal in size to a Celsius degree K = o C + 273

Metric Unit Prefixes Used to make the base units larger or smaller so that they are more convenient to use PrefixSymbolMagnitudeMultiple of base unit Kilok10 3 1,000 Hectoh Deckada Decid Centic Millim

Conversions to Know 1 Mm = 1 x 10 6 m 1 km = 1000 m 100 cm = 1 m 1000 mm = 1 m 1 x 10 6 μm = 1 m Can represent meters, grams, liters

Significant Figures

Uncertainty in Measurement Measurements are uncertain –Measuring instruments are never completely flawless –Measuring always involves some estimation

Measuring Practice

Significant Digits/Figures All the certain digits in a measured quantity and 1 estimated digit of measurement. Rules for determining Significant figures: see handout

Study Buddy Review: Identify S.F mL mg km x 10 6 lbs L dogs cats 8.14, carrots

Study Buddy Review: Identify S.F mL mg km x 10 6 lbs L dogs cats4 8.14, carrots7