1. Homework: Due Friday 9/4 Do 1-10 on a separate sheet of paper, include units. Do all problems on slide 25 as well.

2. SI Units QuantityBase UnitSymbol Length Mass Time Temp meter kilogram second kelvin m kg s K Amountmolemol

3. Accuracy vs. Precision Accuracy - how close a measurement is to the true value Precision - how close a set of measurements are to each other ACCURACY = CORRECTNESS PRECISION = CONSISTENCY

5. Percent Error Indicates accuracy of a measurement.

6. Percent Error Julie determines the density of copper to be 8.25 g/cm 3. Find the % error if the actual density of copper is 8.92 g/cm 3. % error = 7.51 %

7. Precision This is the repeatability of a measurement. It may or may not be accurate But everyone who does it gets the same answer

8. Accuracy vs. Precision Which of the following will allow measurement of a liquid’s volume with the greatest precision? A 50 mL cylinder graduated in 1 mL increments B 50 mL cylinder graduated in 0.5 mL increments C 100 mL cylinder graduated in 1 mL increments D 200 mL cylinder graduated in 5 mL increments Answer: B

9. Significant Figures (Sig Figs) Indicate precision of a measurement. Recording Sig Figs –Sig figs in a measurement include the known digits plus a final estimated digit 2.33 cm

17. If the decimal is present, start on the Pacific side at the first nonzero digit and count it and all the digits to the right of it. If the decimal is absent, start on the Atlantic side at the first nonzero digit and count it and all the digits to the left of it. Pacific (Present) Atlantic (Absent)

18. 4. 0.080 3. 5,280 2. 402 1. 23.50 Significant Figures Counting Sig Fig Examples 1. 23.50 2. 402 3. 5,280 4. 0.080 = ____ sig figs

19. Measurement Unit Conversions

24. Significant Figures 5. (15.30 g) ÷ (6.4 mL) Practice Problems = _______ g/mL 6. (18.9 g) - (0.86 g) = _______ g

26. Scientific Notation Converting into Sci. Notation: –Move decimal until there’s 1 digit to its left. Places moved = exponent. –Large # (>1)  positive exponent Small # (<1)  negative exponent –Only write sig figs.

27. Write these in Scientific Notation 7. 2,400,000  g 8. 0.00256 kg 9.7  10 -5 km 10.6.2  10 4 mm Practice Problems