1. Name_____________________ Block____ Chemistry - Chapter 3 Reading Measurements, Significant Figures, SI Units and Dimensional Analysis

2. Uncertainties in Measurement  Quantitative Measurements depend upon: 1.Reliability of the measuring instrument… Graduated cylinders, balances, thermometers, and rulers all have limitations in the information that they provide. 2.The care with which it is read –this is determined by YOU!  These are the UNCERTAINTIES of Measurement.

3. Uncertainty in measurement  How many numbers can I write down, legitimately, when I make a measurement?  You are allowed to write down all numbers that are measured with certainty plus one that is estimated.  Significant figures in a measurement include all of the digits that are known, plus one more digit that is estimated.

4. To read a measurement using correct sig. figure: If the size of each interval is 1 cm (there is 1 cm between lines), you can guess digit to the 0.1 place  3.5cm Since the size of each interval is 0.1 cm, you can guess digit to the 0.01 place  3.52 cm

5. Which measurement is the best?

6. Read the measurements using correct number of sig. figs.

8. How to determine number of Significant Figures?  Measurements must be reported to the correct number of significant figures.  How Do I Determine the Number of Significant Figures … Go by the RULES !!  Are you ready for the RULES??

9. Rules for Significant Figures  Rule 1 – Nonzeros always count as significant figures. The measurements 24.7 m, 0.743 m, and 714 m each have three significant figures.  Rule 2 – Zeros appearing between nonzero digits are significant. The measurements 7003 m, 40.79 m, and 1.503 m each have four significant figures.  Rule 3 – Leading zeros appearing in front of nonzero digits are not significant. The measurements 0.0071m, 0.42 m and 0.000099 m each have two significant figures.

10. Rules for Significant Figures… Cont’d  Rule 4 – Trailing zeros are significant only if the number contains a decimal point. The measurements 43.00 m, 1.010 m, and 9.000 m each have four significant figures.  Rule 5 – Two special situations have an unlimited number of significant figures: 1. Counted items example, 23 people or 425 thumbtacks 2. Exactly defined quantities example, 60 minutes = 1hr or 100 cm = 1 m

11. Atlantic Pacific Rule for Significant Figures

12. Now it is your turn!!! How many Significant figures are in each of the following measurements? 1.123 cm 2.40,506 mm 3.22 meter sticks 4.0.07080 m 5.98,000 km 6.9.8000 x 10 3 m

13. Significant figures in calculations  In general a calculated answer cannot be more precise than the least precise measurement from which it was calculated.  Ever heard that a chain is only as strong as the weakest link?  Sometimes, calculated values need to be rounded off.

14. Rounding calculated answers Rounding  Decide how many significant figures are needed (more on this very soon)  Round to that many digits, counting from the left  Is the next digit less than 5? Drop it.  Next digit 5 or greater? Increase by 1 Example, round 314.721 m to 4 sig figs  314.7 m round 0.001775 m to 2 sig figs  0.0018 m

15. Rounding calculated answers Addition and Subtraction with Sig. Figs TThe answer should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places.  Example, 6.8 cm + 11.934 cm = 18.734 cm  18.7 cm

16. Rounding calculated answers Multiplication and Division with Sig. Figs  The answer should be rounded to the same number of significant figures as the measurement with the least number of significant figures.  Example, 6.38 mm x 2.0 mm = 12.76 mm  13 mm (2.0 mm has two significant figures—the least)

17. Metric (SI) System and English (Imperial) System  Measurements depend upon units that serve as reference standards.  The standards of measurement used in science are those of the Metric system.  Metric System was revised and named as the International System of Units (SI), as of 1960.  The SI system has 7 base units.  English (Imperial) System is the old system.  The U.S. stands along with Liberia and Burma in using the English system. The rest of the world uses Metric system.

18. SI Base Units

19. Nature of measurements Quantitative measurements consist of 2 parts:  Part 1 – number  Part 2 – unit Examples:  20 grams  75 km/hour

20. SI Units  Sometimes, non-SI units are used. Ex. pound, degree Fahrenheit.  Some are derived units—they are made by joining other units. Examples, Speed = miles/hour (distance/time) Density = grams/mL (mass/volume)

21. Prefixes convert the base units into units that are appropriate for the item being measured.

22. KILO 1000 Units HECTA 100 Units DECA 10 Units DECI 0.1 Unit CENTI 0.01 Unit MILLI 0.001 Unit Meters Liters Grams Metric Conversions Ladder Method How do you use the “ladder” method? 1 st – Determine your starting point. 2 nd – Count the “jumps” to your ending point. 3 rd – Move the decimal the same number of jumps in the same direction. 4 km = _________ m 1 2 3 How many jumps does it take? Starting Point Ending Point 4. 1 __. 2 3 = 4000 m

23. Units of Length  In SI, the basic unit of length is meter (m)  Length is distance between 2 objects  Common metric units of length - cm, m and km.  Can you estimate the following? 1. height of a doorknob from floor 2. width of a shirt button 3. thickness of dime 4. thickness of RNA molecule

24. Units of Mass  Mass is a measure of the quantity of matter present.  Weight is a force that measures the pull by gravity.  Note: Mass is constant, regardless of location but weight changes with location  The SI unit of mass is the kilogram (kg)  Common metric units of mass - mg, g and kg.

25. Units of Volume  Volume – space occupied by any sample of matter.  Calculated for a regular solid by multiplying the length x width x height; thus derived from units of length. SI unit = cubic meter (m 3 )  Common units - cubic centimeter (cm 3 ), L, mL.  Note: 1mL = 1cm 3

26. Temperature  Temperature is a measure of how hot or cold an object is. It determines direction of heat transfer.  Heat moves from the object at the higher temperature to the object at the lower temperature.  We use two units of temperature: Celsius – named after Anders Celsius Kelvin – named after Lord Kelvin

27. Units of Temperature  Celsius scale is defined by: Freezing point of water = 0 0 C Boiling point of water = 100 0 C To convert from 0 F to 0 C : 0 C = 5/9 ( 0 F – 32)  Kelvin scale is represented by K absolute zero = 0 K or -273 0 C formula to convert: K = 0 C + 273

28. Density The formula for density is: mass volume  Common units are: g/mL, g/cm 3, or g/L.  Note: Density does not depend upon sample size.  Relationship between density and temperature: The density of a substance generally decreases as its temperature increases.

29. Dimensional Analysis  Is a way to analyze and solve problems using the units, or dimensions, of the measurements.  Alternative approach to problem solving.  Express 32 minutes in seconds. 1 minute = 60 sec (This is a Conversion Factor) 32 minutes x 60 seconds = 1920 seconds. 1 1 minute