Starter

1. Starter • Convert 6 years to weeks, then to days, then to hours, then to minutes, then to seconds. 312 wks, 2191.50 days, 52596 hrs, 3155760 min, 189345600 sec

2. Here is what we are doing today: • Notes – Units of measurement • Wkst – Metrics & Percent Error • Hmwk – Take home lab (due Monday!)

3. 2.2 Units of Measurement

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 being measured • 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 of 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 • In chemistry, grams (g) is more common • 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. Length • SI unit: m • km is used instead of miles for highway distances and car speeds in most countries

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

11. Volume • amount of space occupied by object • SI: m3 = m x m x m • We will use mL (cm3) more than m3 • non-SI: 1 liter = 1000cm3 = 1000mL

12. ratio of mass to volume SI: Density • characteristic property of substance (doesn’t change with amount ) because as volume increases, mass also increases • density usually decreases as T increases • exception: ice is less dense than liquid water so it floats

13. Example A sample of aluminum metal has a mass of 8.4 g. The volume is 3.1 cm3. Find the density.

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 units to find a connection • always begin with the number and unit you are given with a 1 below it

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

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

20. Starter • Convert 3.76 mm to Mm.

21. 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

22. 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

23. 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

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

25. 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