Starter

1. Starter • Convert 3 years to weeks then to days then to hours then to minutes then to seconds.

2. Ch 2.2 Units of Measurement

3. Measurement 2 types of info: • Quantitative-numerical (usually numbers) • Qualitative- descriptive (usually words)

4. Measurement • Quantitative information • Need a number and a unit (most of time) • Represents a quantity • For example: 2 meters • 2 is number • Meters is unit • Length is quantity • Units compare what is being measured to a defined measurement standard

5. SI Measurement • Le Systeme International d’Unites : SI • System of measurement agreed on all over the world in 1960 • Contains 7 base units • units are defined in terms of standards of measurement that are objects or natural occurrence that are of constant value or are easily reproducible • We still use some non-SI units

6. Important SI Base Units

7. Prefixes • Prefixes are added to the base unit names to represent quantities smaller or larger

8. Mass • Measure of the quantity of matter • SI unit: kg • use g a lot too • mass vs. weight • weight is the measure of gravitational pull on matter • mass does not depend on gravity • on a new planet, mass would be same but weight could change

9. Mass vs. Weight Mass and weight are often confused but are NOT the same! Mass – measure of the quantity of matter in an object. Weight – a measure of the gravitational pull on matter. Weight will vary with gravitational pull on an object, but mass remains the same.

10. Length • SI unit: m • use cm a lot too • km is used instead of miles for highway distances and car speeds in most countries

11. Derived SI Units • come from combining base units • combine using multiplication or division Examples: 1. Area: A = length x width = m x m = m2

12. Derived SI Units 2. Volume - amount of space occupied by object • SI: m3 = m x m x m • non-SI: can be expressed in liters = L 1 L = 1 dm3 • use cm3 in lab a lot 1 cm3 = 1ml 1 L = ___?___mL = ___?___cm3

13. Density • Ratio of mass to volume • Mass divided by volume • Can be used as one property to identify a substance (doesn’t change with amount ) • Density is constant no matter what the size of the sample because as mass increases so does volume

14. Conversion Factors • ratio that comes from a statement of equality between 2 different units • every conversion factor is equal to 1 Example: statement of equality conversion factor

15. Conversion Factors • can be multiplied by other numbers without changing the value of the number • since you are just multiplying by 1

16. Guidelines for Conversions • always consider what unit you are starting and ending with • if you aren’t sure what steps to take, write down all the info you know about the start and end unit to find a connection • always begin with the number and unit you are given with a 1 below it • always cancel units as you go • the larger unit in the conversion factor should usually have a one next to it

17. Example 1 Convert 5.2 cm to mm • Known: 100 cm = 1 m 1000 mm = 1 m • Must use m as an intermediate

18. Example 2 Convert 0.020 kg to mg • Known: 1 kg = 1000 g 1000 mg = 1 g • Must use g as an intermediate

19. Example 3 Convert 500,000 μg to kg • Known: 1,000,000 μg = 1 g 1 kg = 1000 g • Must use g as an intermediate

20. Advanced Conversions • One difficult type of conversion deals with squared or cubed units • Be sure to square or cube the conversion factor you are using to cancel all the units • If you tend to forget to square or cube the number in the conversion factor, try rewriting the conversion factor instead of just using the exponent

21. Example • Convert: 2000 cm3 to m3 • No intermediate needed Known: 100 cm = 1 m cm3 = cm x cm x cm m3 = m x m x m OR

22. Advanced Conversions • Another difficult type of conversion deals units that are fractions themselves • Be sure convert one unit at a time; don’t try to do both at once • Work on the unit on top first; then work on the unit on the bottom • Setup your work the exact same way

23. Example Known: 1000 g = 1 kg 1000 mL = 1 L • Convert: 350 g/mL to kg/L • No intermediate needed OR

24. Combination Example • Convert: 7634 mg/m3 to Mg/L Known: 100 cm = 1 m 1000 mg = 1 g 1 cm3 = 1 mL 1,000,000 g = 1 Mg 1000 mL = 1 L

25. Conversion Practice • 20kg =________mg • 0.75 L =________mL • 72 quarters =________dollars • 80 days =________sec • 12 dozen donuts =________donuts • 300 yards =________inches

26. Conversion Practice • 20 kg = 20,000,000 mg • 0.75 L = 750 mL • 72 quarters = 18 dollars • 80 days = 6,912,000 sec • 12 dozen donuts = 144 donuts • 300 yards = 10,800 inches

27. 2.3 Using Scientific Measurements

28. Accuracy vs. Precision • Accuracy- closeness of measurement to correct or accepted value • Precision- closeness of a set of measurements

29. Accuracy vs. Precision

31. Percent Error vs. Percent Difference • Percent Error: • Measures the accuracy of an experiment • Can have + or – value

32. Percent Error vs. Percent Difference • Percent Difference: • Used when one isn’t “right” • Compare two values • Measures precision

33. Example • Measured density from lab experiment is 1.40 g/mL. The correct density is 1.36 g/mL. • Find the percent error.

34. Example • Two students measured the density of a substance. Sally got 1.40 g/mL and Bob got 1.36 g/mL. • Find the percent difference.

35. Practice Problems • A student measures the mass of a sample as 9.67 g. Calculate the percent error, given that the correct mass is 9.82g. • A handbook gives the density of calcium as 1.54 g/cm3. What is the percent error of a density calculation of 1.25 g/cm3 bases on lab measurements.

36. Significant Figures • All certain digits plus one estimated digit

37. Determining Number of Sig Figs • All non-zero numbers are sig figs • Zeros depend on location in number: LEADING zeros never count EMBEDDED zeros always count TRAILING zeros only count if there is a decimal point.

38. Location of Zeros • EMBEDDED: between non-zero numbers • All are sig figs • LEADING: at front of all non-zero numbers • None are sig figs • TRAILING: at the end of non-zero numbers • If there is a decimal, all are sig figs • If there is not, none are sig figs

41. Practice 101.02 IMBEDDED 5 20.0 TRAILING w/ 3 0.005302 LEADING 4 17000 TRAILING w/o 2 4320. TRAILING w/ 4

42. Rounding • Need to use rounding to write a calculation correctly • Calculator gives you lots of insignificant figures and you must round to the right place • When rounding, look at the digit after the one you can keep • Greater than or equal to 5, round up • Less than 5, keep the same

43. Examples Make the following have 3 sig figs: • 761.50  762 • 14.334  14.3 • 10.44  10.4 • 10789  10800 • 8024.50  8020 • 203.514  204

44. Using Sig Figs in Calculations • Adding/Subtracting: • end with the least number of decimal places

45. Using Sig Figs in Calculations • Adding/Subtracting: • end with the least number of decimal places

46. Using Sig Figs in Calculations • Multiplying/Dividing: • end with the least number of sig figs

47. Using Sig Figs in Calculations • Multiplying/Dividing: • end with the least number of sig figs

48. Scientific Notation • condensed form of writing large or small numbers • form: M x 10n • M must be: • greater than or equal to 1 • less than 10 • n must be: • whole number • positive or negative

49. Scientific Notation • Find M by moving decimal point over in the original number to left or right so that only one non-zero number is to left of decimal

50. Scientific Notation • Find n by counting number of places you moved the decimal : to left (+) or to right (-)