Day 3 - Notes Unit 1: Introduction to Chemistry Types of Measurements and Observations, Scientific Notation Please enjoy this free measurement Power Point. If you like the quality of my work, please stop by my TpT store for more lesson plans, homeworks, assessments, and lab activities. http://bit.ly/MsRazzChemClass
Measurement: a type of observation • Qualitative measurements: descriptive • Ex: hot, cold, heavy, light, big, blue, furry • Quantitative measurement: observation made with a measuring instrument and includes both a number and a unit • Ex: ruler, balance, thermometer, graduated cylinder, 13.5°C, 25kg, 17L
Accuracy: How close a measurement is to the true or accepted value • Ex: Weighing a 50g mass 50.00g – accurate 32.18g – not accurate 49.99g – accurate
Precision: How close multiple measurements are to each other • Ex: Take the weight of a 50g mass Accurate, precise: Accurate, precise: 50.00g 50.00g 50.00g 49.99g 50.00g 50.00g Not accurate, precise: 32.18g 32.18g 32.18g
An easy way to remember… ACcurate = Correct PRecision = Reproducibility
Significance in Measurement • . • Which of the following best describes the length of the beetle's body in the picture to the left? • Between 0 and 2 in • Between 1 and 2 in • Between 1.5 and 1.6 in • Between 1.54 and 1.56 in • Between 1.546 and 1.547 in
Significance in Measurement • The correct answer is . . . (d), between 1.54 and 1.56 inches
Significance in Measurement • Measurements are often written as a single numberrather than a range. • The beetle's length in the previous frame was between 1.54 and 1.56 inches long. • The single number that best represents the measurement is the center of the range, 1.55 inches. • When you write the measurement as a single number, it's understood that the last figure (the second of the two 5’s in this case) had to be estimated. Consider measuring the length of the same object with two different rulers.
Significance in Measurement • . • For each of the rulers, give the correct length measurement for the steel pellet as a single number rather than a range
Significance in Measurement • For the ruler on the left you should have had . . . 1.4 in • For the ruler on the right, you should have had . . . 1.47 in
Significance in Measurement • A zero will occur in the last placeof a measurement if the measured value fell exactly on a scale division. • For example, the temperature on the thermometer should be recorded as 30.0°C. • Reporting the temperature as 30°Cwould imply that the measurement had been taken on a thermometer with scale marks 100°C apart!
Significance in Measurement • Use the bottom of the meniscus (the curved interface between air and liquid) as a point of reference in making measurements of volume in a graduated cylinder, pipet, or buret. • In reading any scale, your line of sight should be perpendicular to the scale to avoid 'parallax' reading errors.
Significance in Measurement • The graduated cylinder on the right has scale marks 0.1 mL apart, so it can be read to the nearest 0.01 mL. • Reading across the bottom of the meniscus, a reading of 5.72 mL is reasonable (5.73 mL or 5.71 mL are acceptable, too).
Significance in Measurement • Determine the volume readings for the two cylinders to the right, assuming each scale is in mL.
Significance in Measurement • For the cylinder on the left, you should have measured . . . 3.0 mL • For the cylinder on the right, you should have measured . . . 0.35 mL