PP 4 units of measurement and precision vs accuracy 1 3 4

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Units of Measurement Precision vs Accuracy Sections 1.3 and 1.4 Types of Observations and Measurements  We make QUALITATIVE observations of reactions — changes in color and physical state  We also make QUANTITATIVE observations that involve MEASUREMENTS with numbers and units NO NAKED NUMBERS A measurement always has two parts: A value (this is the number) A unit of measure (this tells what you have) Example: 200 meters; 15 ml; 13.98 grams  In Chemistry we use SI Units of measure International System of Units  These are the base units that we will be working with:  From these base units, we can combine them using mathematical operations to obtain derived units  Some of the derived units we will be using include:  Density (g/ml)  Area (m2)  Volume (m3) Prefixes Used in the SI System Metric Prefixes  Kilo- means 1000 of that unit  kilometer (km) = 1000 meters (m)  Centi- means 1/100 of that unit  meter (m) = 100 centimeters (cm)  dollar = 100 cents  Milli- means 1/1000 of that unit  meter (m) = 1000 millimeters (mm) To convert from one metric unit to another remember this King–Henry Died (Unexpectedly) Drinking Chocolate Milk pneumonic: You must also know… …how to convert within the Metric System Here’s a good device: On your paper draw a line and add tick marks: Next: Above the tick marks write the abbreviations for the King Henry pneumonic: k h d (u ) d m l g Write the units in the middle under the “U” c m Solution Classify each of the following as an exact (e) or a measured(m) number Give reason A m Requires a thermometer(measuring tool) B e From a definition in U.S system C m Need measuring tool to determine D e Counted the hats E m Measured  Two types of instruments used to take measurements  Digital display -measurement is displayed electronically by machine (Ex: electronic balance)  Scaled instrument -instruments has numbered lines to determine measurement (Ex: ruler)  REMEMBER TO INCLUDE THE DIGIT OF UNCERTAINTY IN YOUR MEASUREMENT A digit that must be estimated is called uncertain  A measurement always has some degree of uncertainty  Record the certain digits and the first uncertain digit (the estimated number)   Graduated cylinders shows each line (scale) represents ml increments  This instrument is accurate to ones place, therefore estimated digit should be in tenth place  For scaled instruments the estimated digit must be determined by YOU  Liquid volume is 43.0 ml not 43 ml The zero, in tenth place, is the estimated digit Measurement of Volume Using a The volume is read at the bottom of the liquid curve Buret (meniscus)   Meniscus of the liquid occurs at about 20.15 mL  Certain digits: 20.15  Uncertain digit: 20.15  Electronic thermometer is an example of a instrument that uses digital display  The last digit in these types of instruments is the estimated digit and is always supplied  The in the tenth place in the estimated digit  32.6 oC is the correct reading  All measurements have some degree of uncertainty WHY?????  When measurements are recorded CORRECTLY it must be written with a digit of uncertainty (estimated digit) and a unit  Last digit in ANY measurement is the digit of uncertainty (estimated digit) Precision and Accuracy Accuracy • Agreement of a particular value with the true value Precision • Degree of agreement among several measurements of the same quantity Measurement  Accurate means "capable of providing a correct reading or measurement."  In Chemistry: it means 'correct‘ How close you are to the accepted value Measurement Accurate Measurement Precise X X X X X X Measurement Can you be neither accurate or precise? Measurement x This is a random like pattern, neither precise nor accurate The darts are not clustered x together and are not near the bull's eye x x x Measurement This is an accurate pattern, but not precise The darts are x not clustered, but their 'average' position is the center x x x x of the bull's eye Measurement This pattern is both precise and accurate The darts are tightly clustered and their average position is the center of the bull's eye xxxx x [...]... amount of matter in an object (grams, measured with a BALANCE) What is a Liter?? Measuring Volume: measured with a  The volume of a liquid is graduated cylinder When liquid is poured into the cylinder, a curved surface called the meniscus is formed Learning Check 1 1000 m = 1 _ a) mm b) km c) dm a) mg b) kg c) dg 2 0.0 01 g = 1 _ 3 0 .1 L = 1 _ a) mL b) cL c) dL 4 0. 01 m = 1 _ a) mm b) cm c) dm 1 1000... digit and is always supplied  The 6 in the tenth place in the estimated digit  32 .6 oC is the correct reading  All measurements have some degree of uncertainty WHY?????  When measurements are recorded CORRECTLY it must be written with a digit of uncertainty (estimated digit) and a unit  Last digit in ANY measurement is the digit of uncertainty (estimated digit) Precision and Accuracy Accuracy... volume is 43 .0 ml not 43 ml The zero, in tenth place, is the estimated digit Measurement of Volume Using a The volume is read at the bottom of the liquid curve Buret (meniscus)   Meniscus of the liquid occurs at about 20 .15 mL  Certain digits: 20 .15  Uncertain digit: 20 .15  Electronic thermometer is an example of a instrument that uses digital display  The last digit in these types of instruments... relationship 1 foot = 12 inches 1 meters = 10 0 cm  Not obtained with measuring tools  We will later learn that these numbers do not limit the number of significant figures reported Learning Check Classify each of the following as an exact(e) or a measured (m) number A. _Gold melts at 10 64 C B. _1 yard = 3 feet C. _A red blood cell with diameter 6 x 10 -4 cm D. _There were 6 hats on the shelf E. _A can of. .. b) cm c) dm 1 1000 m = 1 _ a) mm a) mg b) km b) kg c) dm 2 0.0 01 g = 1 _ c) dg 3 0 .1 L = 1 _ a) mL b) cL c) dL 4 0. 01 m = 1 _ a) mm b) cm c) dm Measured Numbers When you use a measuring tool is used to determine a quantity such as your height or weight, the numbers you obtain are called measured numbers Exact Numbers  Obtained when you count objects 2 soccer balls 1 watch 4 pizzas  Obtained from... meter, liters, and grams: k h d hm dam kl hl kg hg km u d c m m dm cm dal l dl cl ml dag g dg cg mg mm How to use this device: 1 Look at the problem Look at the unit that has a number On the device put your pencil on that unit 2 Move to new unit, counting jumps and noticing the direction of the jump 3 Move decimal in original number the same # of spaces and in the same direction Example #1: (1) Look at... measurement is the digit of uncertainty (estimated digit) Precision and Accuracy Accuracy • Agreement of a particular value with the true value Precision • Degree of agreement among several measurements of the same quantity Measurement  Accurate means "capable of providing a correct reading or measurement. "  In Chemistry: it means 'correct‘ How close you are to the accepted value ... has numbered lines to determine measurement (Ex: ruler)  REMEMBER TO INCLUDE THE DIGIT OF UNCERTAINTY IN YOUR MEASUREMENT A digit that must be estimated is called uncertain  A measurement always has some degree of uncertainty  Record the certain digits and the first uncertain digit (the estimated number)   Graduated cylinders shows each line (scale) represents 1 ml increments  This instrument... unit k km h hm d dam u d m dm c cm m mm Example #1: 2 Move to new unit, counting jumps and noticing the direction of the jump! Be careful NOT to count the spot you start from, where you put your pencil point Only count the jumps! k d c dm cm km h hm d dam u m One jump to the right! m mm Example #1: 3 Move decimal in original number the same # of spaces and in the same direction 56 cm = _ mm 56.0 One... Answer: Example #2: (1) Look at the problem 7.25 L = kL Look at the unit that has a number 7.25 L k h d u d c m On the device put your pencil on that unit kl hl dal L dl cl ml Example #2: 2 Move to new unit, counting jumps and noticing the ddirection of the jump! k h u d c m kL hL daL L dL cL Three jumps to the left! mL Example #2: (3) Move decimal in original number the same # of spaces and in the same
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