1. Chemistry is an observation science Observations frequently require taking measurements Measurements have some degree of uncertainty All measured numbers have 2 parts: Chapter 2: Measurements in Chemistry

2. Scientists use the Metric System: Units of Measurement MeasurementMetric Base Unit Length Volume Mass Temperature Time

3. PrefixSymbolNumerical ValueSci Notation Equality Prefixes that Increase the Size of the Unit: GigaG1,000,000,0001 x 10 9 megaM1,000,0001 x 10 6 1 Mg = 10 6 g or 1 g = 10 -6 Mg kilok1,0001 x 10 3 1 km = 1000 m or 1 m = 10 -3 km Prefixes that Decrease the Size of the Unit: decid0.11 x 10 -1 1 dL = 0.1 L or 1 L = 10 dL centic0.011 x 10 -2 1 cm = 0.01 m or 1 m = 100 cm millim0.0011 x 10 -3 1 ms = 10 -3 s or 1 s = 1000 ms micro  0.0000011 x 10 -6 1  g = 10 -6 g or 1 g = 10 6  g nanon0.0000000011 x 10 -9 Metric Prefixes:

4. What is the relationship between volume and length? 1 Liter = the space occupied by a 10 cm cube

5. Exact and Inexact Numbers? Exact number = number whose value has no uncertainty defined numbers counted numbers Inexact number = a number with a degree of uncertainty measured numbers

6. Uncertainty in Measurement Significant figures = all digits that are known with certainty + 1 estimated digit

8. Precision = the degree to which a measurement is reproducible The precision of a measurement is determined by the instrument used: Digital equipment – record all digits Analog equipment – incremental (closest) marks

9. Guidelines for Determining Significant Figures in Measured Numbers Significant Figures Digits known with certainty + one estimated digit Nonzero Digits 1, 2, 3 … 9 are always significant Zero May or may not be significant Leading Zeros Zeros at the beginning of a number are never significant Trailing Zeros Are significant only if the decimal point is shown Confined Zeros Zeros between non-zero digits are always significant

10. How many Significant Figures? 562.000.03345,100348 Calculations & Significant Figures: The answer to a calculation involving measured numbers cannot have greater significance than any of the measurements! Addition and Subtraction: The answer has the same precision as the least precise measurement. Example: A graduted cylinder contained 25.5 ml of water. A glass marble was added to the cylinder and the volume reading increased to 33.2 ml. What was the volume of the marble?

11. Multiplication and Division: The answer has the same number of significant figures as the measurement with the fewest significant figures. Example: The marble (from the previous example) has a mass of 22.0186 grams. What is it’s density? Rules for rounding: If the digit to be dropped is less than 5, simply drop it If the digit to be dropped is 5 or greater, round up Round to 2 significant figures: 258.59 0.06617182,540

12. Perform the following calculations involving measured numbers, express your answer to the proper number of significant figures: a) 6.731 x 0.0021 = b)8.4 1.8 + 5.2 c) 120  0.0045 = (write the answer in scientific notation)

13. Scientific Notation: a convenient way of expressing large or small numbers

14. A number in Scientific Notation has 2 parts: coefficient - a number between 1 and 10 it includes only significant figures exponential term – a number expressed as x 10 n n = an integer (positive or negative) Convert to scientific notation: 47,0000.00211 Convert to standard notation: 5.442 x 10 3 8.25 x 10 -5 1.23 x 10 -34

15. Scientific Notation & Calculators: -enter the coefficient as you would for a regular number -press EXP or EE -enter the exponent Examples: a. (9.41 x 10 12 ) x (2.7722 x 10 -5 ) = b. (2.5 x 10 4 )  (6.8 x 10 6 ) =

16. Conversion Factors—Metric System: What does it mean? 1 cm = 0.01 meter or 100 cm = 1 meter Write the equality as a ratio: A ratio can be used as a conversion factor.

17. Consider a meterstick: 1 meter = 100 cm How many cm are equal to 2.5 meters? 1 meter = 1000 mm How many meters are equal to 650 mm?

18. Unit Conversion within the Metric System: Start with the given measured number What units are to be changed? Find the relationship between units (equality) Write as a ratio with the “old” unit in the denominator & the “new” unit in the numerator Cancel the units Multiply/divide the numbers Record your answer to the proper number of sig. figs. a. Convert 1.5x10 5 milliseconds (ms) to seconds b. Convert 35 microliters (  L) to Liters c. Convert 2130 decigrams (dg) to kilograms (kg)

19. Unit Conversion within the English System: a. Convert 349 inches to feet

20. English-to-Metric & Metric-to-English Conversions: Example: Convert 128 lb to kiligrams Example: Convert 36.5 inches to cm

21. Example: Convert 650 ml to cm 3. Recall the relationship between volume and length: 1 Liter = the space occupied by a 10 cm cube

22. Multistep conversions: Start with the given measured number What units are to be changed? (make a unit map) Find the relationship between units for each step Write each as a ratio with the “old” unit in the denominator & the “new” unit in the numerator Write the conversion as a series of multiplication steps. Cancel the units Multiply/divide the numbers Record your answer to the proper number of sig. figs. Example: convert 9.85 Liters to gallons (given that 1 Liter = 1.057 qt; 1 gallon = 4 qt.)

23. Example: Convert 35 mi/hr to m/min (given that 1 mile = 1609 meters) Example: A 150 lb. man requires a drug dosage of 2.5 mg/kg. How many milligrams of the drug should he take? (1 kg = 2.205 lb.)

24. Converting squared or cubed units: 1.Convert 0.25 m 2 to cm 2. 2.One side of a sheet of paper has an area of 93.5 in 2. Convert this to square cm?

25. Density = mass volume

26. Density = mass volume Example: A piece of metal has a mass of 78.12 g and a volume of 9.5 cm 3. What is it’s density? What metal is it? Metal Density ( g/cm 3 ) Mg 1.7 Al 2.7 Zn 7.1 Sn 7.3 Fe 7.9 Brass 8.4 Cu 8.9 Pb 11.4 Au 19.3 Pt21.1 Density Animation http://www.wiredchemist.com/anim-density

27. Example: A shiny gold-colored nugget has a mass of 26.5 grams and a volume of 3.4 cm 3. Is it gold? Example: Carbon dioxide has a density of 0.001963 g/ml. What is the mass of a 5.0Liter sample of CO 2 ?

28. Example: An empty graduated cylinder has a mass of 215 grams. After filling it with liquid (946 ml) it is weighed again; the mass of the cylinder + liquid is 1854 grams. What is the density of the liquid? 215 grams 1854 grams

29. Temperature - a measure of the intensity of heat Temperature Scales: Celcius (  C) Fahrenheit (  F) Kelvin (K)

30. Conversions between temperature scales: Converting from Celcius to Fahrenheit: A mixture of salt and water has a temperature of -5.0  C. What is the temp on the Fahrenheit scale?

31. Converting from Fahrenheit to Celcius: A child has a temperature of 103.1  F. What is the temp on the Celcius scale? Converting from Celcius to Kelvin: On the planet Mercury, the average daytime temperature is 683 K. What is the temp on the Celcius scale?