Chapter 2 Standards of Measurement Objectives:  Understand Mass and Weight (2.1)  Identify the metric units of measurement (2.6)  Explain what causes.

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Chapter 2 Standards of Measurement Objectives:  Understand Mass and Weight (2.1)  Identify the metric units of measurement (2.6)  Explain what causes uncertainty in measurements (2.7, 2.8 – 2.12)  Learn how to use significant digits and scientific notation (2.2 – 2.5)  Dimensional Analysis (2.8)  Density (2.12)

The Metric System (2.6) The International System of Units Standards of measurement Base units (7) – see Table 2.2 (pg 20) 1.MASS: 2.LENGTH: 3.TIME: 4.COUNT, QUANTITY: 5.TEMPERATURE: 6.ELECTRIC CURRENT: 7.LUMINOUS INSTENSITY:

The Metric System Derived Units:  AREA:  VOLUME:  ENERGY:  FORCE:  PRESSURE:  POWER:  VOLTAGE:  FREQUENCY:  ELECTRIC CHARGE:

The Metric System Metric Prefixes – make base unit larger or smaller Table 2.1 – must know bolded prefixes Based on 10 Math method vs. “Stairs”

Convert a volume of 12 microliters into centiliters Express a distance of 15 meters in kilometers Which is the longer amount of time, 1351 ps or 1.2 ns? Conversion Practice

Uncertainty in Measurement Why are digits in measurements uncertain? 1.Instruments never completely free of flaws 2.Always involves estimation  Choose the right instrument for the job  May be estimated for you (electronic scales)  Scale is marked but you estimate the in- between

Uncertainty in Measurement Precision:Accuracy:

Significant Digits All digits known with certainty plus one final digit which is uncertain (or estimated) All non-zeros are significant (143.34) A zero is significant when : –It is between nonzero digits (2004) – A zero is not significant when: – –

Significant Digits - PRACTICE How many significant digits? 1. 54.23 2. 23.00005 3. 0.0004 4. 35000 5. 0.000504 6. 45.623200 7. 5,000,000 8. 4,000,000.1

Significant Digits - Calculations Addition and Subtraction –Round answer to have final digit in the SAME PLACE as the last digit in the LEAST ACCURATE MEASUREMENT 1.21 + 5.002 + 10. = 34.5 + 12.45 + 23.0505 = 186.31 + 11.1 = 12.0231 + 3.86 = 0.100012 + 120. = 1200 + 12 + 15 + 0.5 = 1200 + 12 + 15 + 0.5 =

Significant Digits - Calculations Multiplication and Division –The answer has as many sig figs as the number with the 14.8 x 3.1 = 18.2 x 3.0 = 52/1.5 = 321.868783 x 1 = 2400 x 2.123 = 15000/12.354 =

Scientific Notation Convenient way of writing very large or very small numbers and showing only significant figures Number between 5120 becomes Move decimal point in original number to make number Move left = ; move right =

Scientific Notation Practice 123,000 = 0.000045 = 23.45 = 0.0000000003 = 1,000,000 =

Scientific Notation Adding and subtracting –Numbers must be the SAME POWER –1.4 x 10 4 + 2.1 x 10 5 (must change to 21.0 x 10 4 ) and then = –3.2 x 10 3 + 1.8 x 10 2 =

Scientific Notation Multiplying – –(2.0 x 10 3 ) x (3.0 x 10 4 ) = Dividing – –(8.2 x 10 8 ) / (4.1 x 10 4 ) =

Types of Measurements Mass – amount of matter in a body – Weight – measure of earth’s gravitational attraction for that object – –

Types of Measurements Volume – the amount of space occupied by matter – – Temperature – measure of the intensity of heat (figure 2.6) – – –

Conversion Factors Enable movement between metric system and “English” system See back cover of book and Appendix III Common conversions you should memorize

Dimensional Analysis (Problem Solving) Remember: A technique of converting between units

Dimensional Analysis (Problem Solving) Conversion Factors: ratio derived from the equality between 2 different units CF can be written either way

Dimensional Analysis (Problem Solving) The “t” method Conversion Factor

How many seconds are in 4.15 hours? Dimensional Analysis (Problem Solving) If a student needs 1.5 mL of water, how many cups does he need?

Density Common ratio used in chemistry Physical property of a substance Mass/volume D = m v SI units: kg/m 3 Solid –g/cm 3Liquid –g/mLGas –g/L Can change due to temperature and/or pressure changes

Density 1.Find the density of a piece of metal with a volume of 2.7 cm 3 and a mass of 10.8 g. 2. Determine the mass of an object with a density of 0.24 g/cm 3 and a volume of 2 cm 3. !!!

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