Welcome to AP Chemistry

1. Welcome to AP Chemistry

2. Significant figures • Meaningful digits in a MEASUREMENT • Exact numbers are counted, have unlimited significant figures • If it is measured or estimated, it has sig figs. • If not it is exact. • All numbers except zero are significant. • Some zeros are, some aren’t

3. Which zeroes count? • In between other sig figs does • Before the first number doesn’t • After the last number counts if: • it is after the decimal point • the decimal point is written in • 3200 2 sig figs • 3200.4 sig figs

4. Doing the math • Multiplication and division, same number of sig figs in answer as the least in the problem • Addition and subtraction, same number of decimal places in answer as least in problem.

5. More Preliminaries Scientific Method Metric System Uncertainty

6. Scientific method. • A way of solving problems • Observation- what is seen or measured • Hypothesis- educated guess of why things behave the way they do. (possible explanation) • Experiment- designed to test hypothesis • leads to new observations, • and the cycle goes on

7. Scientific method. • After many cycles, a broad, general explanation is developed for why things behave the way they do • Theory • Also regular patterns of how things behave the same in different systems emerges • Law • Laws are summaries of observations

8. Scientific method. • Theories have predictive value. • The true test of a theory is if it can predict new behaviors. • If the prediction is wrong, the theory must be changed. • In Short: Theory- why Law - how

9. Theory (Model) Law Observations Hypothesis Modify Experiment Prediction Experiment

10. Metric System • Every measurement has two parts • Number and a Scale (unit) • SI system (le Systeme International) based on the metric system • Prefix + base unit • Prefix tells you the power of 10 to multiply by - decimal system -easy conversions

11. Metric System • Base Units • Mass - kilogram (kg) • Length- meter (m) • Time - second (s) • Temperature- Kelvin (K) • Electric current- ampere (amp, A) • Amount of substance- mole (mol)

12. Prefixes • giga- G 1,000,000,000 109 • mega - M 1,000,000 106 • kilo - k 1,000 103 • deci- d 0.1 10-1 • centi- c 0.01 10-2 • milli- m 0.001 10-3 • micro- m 0.000001 10-6 • nano- n 0.000000001 10-9

13. Deriving the Liter • Liter is defined as the volume of 1 dm3 • V = length x width x height

14. Mass and Weight • Mass is measure of resistance to change in motion • Weight is force of gravity on a mass Fw = mass x g (g = 9.8 m/s2) • Sometimes used interchangeably • Mass can’t change, weight can

15. Uncertainty • Basis for significant figures • All measurements are uncertain to some degree • Precision- how repeatable • Accuracy- how correct - closeness to true value. • Better precision implies better accuracy • You can have precision without accuracy • You can’t have accuracy without precision

16. Uncertainty • 2 Types of Error: Random error - equal chance of being high or low- addressed by averaging measurements - expected • Systematic error- same direction each time • Want to avoid this type

17. Dimensional Analysis Using the units to solve problems

18. Dimensional Analysis • Use conversion factors to change the units • Conversion factors = 1 • 1 foot = 12 inches (equivalence statement) • 12 in =1= 1 ft. 1 ft. 12 in • 2 conversion factors • multiply by the one that will give you the correct units in your answer.

19. 1.00 ns Examples • The speed of light is 3.00 x 108 m/s. How far will a beam of light travel in 1.00 ns? 1 x 10-9s 1 ns 3.00 x 108 m 1s = 0.300 m

20. Dealing with Two Units If your pace on a treadmill is 65 meters per minute, how many seconds will it take for you to walk a distance of 8450 feet?

21. What about Square and Cubic units? • Use the conversion factors you already know, but when you square or cube the unit, don’t forget to cube the number also! • Best way: Square or cube the ENITRE conversion factor • Example: Convert 4.3 cm3 to mm3 ( ) 4.3 cm3 10 mm 3 1 cm 4.3 cm3 103 mm3 13 cm3 = = 4300 mm3

22. Learning Check • A Nalgene water bottle holds 1000 cm3 of water. How many cubic decimeters is that?

23. Solution 1000 cm3 1 dm 3 10 cm ( ) = 1 dm3 So, a dm3 is the same as a Liter ! A cm3 is the same as a milliliter.

24. Temperature and Density

25. Temperature • A measure of the average kinetic energy • Different temperature scales, all are talking about the same height of mercury.

26. 100ºC = 212ºF 0ºC = 32ºF 0ºC 100ºC 212ºF 32ºF

27. oF = 1.8(oC) + 32 oC = (oF – 32) / 1.8 K = oC +273 0ºC 100ºC 212ºF 32ºF

28. Density • Ratio of mass to volume • D = m/V • Useful for identifying a compound • Useful for predicting weight • An intrinsic property- does not depend on the quantity of the material

29. Density Problem • An empty container weighs 121.3 g. Filled with carbon tetrachloride (density = 1.53 g/cm3 ) the container weighs 283.2 g. What is the volume of the container? V = m / D m = 161.9 g D = 1.53 g/cm3 V = 161.9 g /(1.53 g/cm3) = 106 cm3

30. Density Problem • A 55.0 gal drum weighs 75.0 lbs. when empty. What will the total mass be when filled with ethanol? density of ethanol is 0.789 g/cm3 1 gal = 3.78 L 1 lb = 454 g 55.0 gal | 3.78 L | 1000 mL | 1 cm3| 0.789 g | 1 lb = 361 lb | 1 gal | 1L | 1 mL | 1 cm3 | 454 g 361 lb + 75.0 lb = 436 lb

31. Grams to Mols to Atoms • Use molar mass to convert from grams to mols or from mols to grams • Conversions involving atoms, molecules, or ions: • use Avogadro’s number 6.02 x 1023 particles/mol

32. % Error = Accepted value – Experimental value x 100 Accepted value Negative % errors are OK