Download presentation

Presentation is loading. Please wait.

Published byBrooke Henry Modified over 6 years ago

1
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)

2
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:

3
The Metric System Derived Units: AREA: VOLUME: ENERGY: FORCE: PRESSURE: POWER: VOLTAGE: FREQUENCY: ELECTRIC CHARGE:

4
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”

5
Convert a volume of 12 microliters into centiliters Express a distance of 15 meters in kilometers Convert 83 cm into meters Which is the longer amount of time, 1351 ps or 1.2 ns? Convert 16 dL into L Conversion Practice

6
Uncertainty in Measurement Why are digits in measurements uncertain? 1.Instruments never 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

7
Uncertainty in Measurement Precision:Accuracy:

8
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 –It is at the A zero is not significant when: –It is before –It is at the

9
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

10
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. = 16.212 becomes 16 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 =

11
Significant Digits - Calculations Multiplication and Division –The answer has as many sig figs as the number with the fewest sig figs 14.8 x 3.1 = 45.88 becomes 46 18.2 x 3.0 = 52/1.5 = 321.868783 x 1 = 2400 x 2.123 = 15000/12.354 =

12
Scientific Notation Convenient way of writing very large or very small numbers and showing Number between 1 & 10 with a 5120 becomes Move decimal point in original number to make Move left = ; move right =

13
Scientific Notation Practice 123,000 = 0.000045 = 23.45 = 0.0000000003 = 1,000,000 =

14
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 = 2.24 x 10 4 –3.2 x 10 3 + 1.8 x 10 2 =

15
Scientific Notation Multiplying –Add exponents –(2.0 x 10 3 ) x (3.0 x 10 4 ) = Dividing –Subtract exponents –(8.2 x 10 8 ) x (4.1 x 10 4 ) =

16
Types of Measurements Mass – amount of matter in a body – – Weight – measure of earth’s gravitational attraction for that object – –

17
Types of Measurements Volume – –Cubic meter or –Many instruments to measure Temperature – –Kelvin –Degrees

18
Conversion Factors Enable movement between metric system and “English” system See back cover of book and Appendix III Common conversions you should memorize –1 inch = 2.54 cm –1 mile = 1.609 km –1 kg = 2.20 pounds –1 mL = 1 cm 3 –0 K = -273.15 0 C – 0 F = 1.8( 0 C) + 32

19
Dimensional Analysis (Problem Solving) Remember: ALWAYS use UNITS OF MEASUREMENT in your work!!! A technique of converting between units –Same system (metrics) –Different systems (inches to meters) –Chemical equations….later chapters…

20
Dimensional Analysis (Problem Solving) Conversion Factors: ratio derived from the equality between 2 different units 3 feet = 1 1 dollar = 1 1 yard4 quarters 1 yard4 quarters CF can be written either way 1 minute = 1 60 seconds = 1 1 minute = 1 60 seconds = 1 60 seconds 1 minute

21
Dimensional Analysis (Problem Solving) The “t” method unit given unit wanted = unit wanted unit given Example: How many liters are in 125.6 gallons? 125.6 gallons3.785 Liters = 1 gallon Conversion Factor 475.4 L

22
4.15 hours 60 minutes60 seconds = 1 hour 1 minute 1.5 mL 1 L 1 gal 4 qts 4 cups = 1000 mL 3.785 L 1 gal 1 qt 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? 14900 s 0.0063 cups

23
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

24
m = d x v = 0.24 g/cm 3 x 2 cm 3 = 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. D = m v = 10.8 g 2.7 cm 3 = 4.0 g/cm 3 2. Determine the mass of an object with a density of 0.24 g/cm 3 and a volume of 2 cm 3. SIG FIGS!!! 0.5 g 0.48

Similar presentations

© 2021 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google