Measurement and Calculation Unit 2

The Fundamental SI Units (la Système Internationale, SI) Physical QuantityNameAbbreviation Mass Length Time Temperature Electric Current Amount of Substance Luminous Intensity kilogram meter second Kelvin Ampere mole candela kg m s K A mol cd

SI Units

SI Prefixes Common to Chemistry Base unit Deci (d) 1/ Centi (c) 1/ Milli (m) 1/ Micro (μ) 1/ Nano (n) Pico (p) Kilo (k) 1, Mega (M) 1,000, Giga (G) 1,000,000,

Scientific Notation A shorthand method of expressing large and small numbers using exponents. Expresses values as a multiple of 10 to a specific power. Must use the correct form when expressing a number in sci not. M x 10 n M = any number between 1 & 10 n = any integer (including 0) Example: 12,480,000 → x → 2.37 x 10 -5

Scientific Notation Express the following in scientific notation: 1. 2,300, Express the following in decimal form: x x 10 -4

Scientific Notation Perform the following calculations, expressing your answer in scientific notation. 1. (6.0 x 10 4 ) (2.0 x 10 5 ) 2. (1.248 x 10 7 )(2.37 x ) 3. (8.0 x 10 3 ) / (2.0 x 10 6 ) 4. (2.0 x ) / (4.0 x ) 5. (5.27 x 10 4 ) + (2.96 x 10 6 ) 1.2 x x x x x 10 6

Accuracy vs. Precision Accuracy refers to how close a measurement is to the true or actual value. Precision refers to how close a series of measurements are to one another.

Reporting Measurements To indicate the uncertainty of a single measurement scientists use a system called significant figures Our data can only be as precise as the least precise measuring tool/instrument

Rules for Counting Significant Figures 1. Nonzero integers are always significant Ex m  3 sig figs g  4 sig. figs 2. ‘0’ between nonzero digits are significant. Ex L  3 sig. figs km  5 sig figs

Rules Continued 3. ‘0’ in front of nonzero digits (leading zeros) are never significant. Ex m  4 sig. figs kg  1 sig. fig. Neither are zeroes at the end of a number Ex g = 2 sig figs *The zeroes in these cases are ‘placeholders’; they are used for spacing.

Rules Continued 4. Zeros at the end of a number and to the right of a decimal are significant. Ex  4 sig. figs  10 sig. figs. 5. A decimal point placed after zeros indicates that the zeros are significant. Ex  1 sig. fig  4 sig. figs.

Rules Continued Do NOT count sig. figs. in the following numbers: 1. Counting numbers 2. Constants which are defined values (1 atm) 3. Conversion factors which are defined relationships (1km = 1000m)

Calculations with Significant Figures Answers to calculations must be rounded to the proper number of significant figures at the end of the calculation.

Adding/Subtracting Numbers with Significant Figures When adding/subtracting, look for the LEAST PRECISE measurement to determine the correct number of sig. figs. Round answer to the same decimal place Ex. 54 g g g = 163 g mL – 2.1 mL = 53.1 mL

Multiplication/Division with Significant Figures Count the number of significant figures in each measurement Round the result so it has the same number of significant figures as the measurement with the smallest number of significant figures 4.5 x = 2 sf3 sf x 10 4 ÷ = = 5.90 x 10 5 Correct?

How HOT are you?? Heat (energy) cannot be measured directly. We can measure heat transfer by change in temperature. We define temperature as the average kinetic energy of a system. movement within a substance Measure temperature with a thermometer.

Temperature Scales Fahrenheit Scale, °F Relative scale Celsius Scale, °C Relative scale Water’s freezing point = 0°C, boiling point = 100°C Kelvin Scale, K Absolute scale Water’s freezing point = 273 K, boiling point = 373 K o C = K K = o C + 273

Graphing 1.Determine the variables. -Independent  x-axis -Dependent  y-axis 2.Determine the range of values. 3.Utilize all of 1 side of the graph paper. -usually start at ‘0’ but NOT ALWAYS 4. Makes scales easy & keep consistent

Graphing 5. Label both axes (include unit). - draw axes with a straight edge 6.Give your graph an appropriate title. - dependent vs. independent 7. Titles, axes, & labels must be in INK! 8. Plot data with ‘x’ not ‘’ (may be in pencil) 9. Draw “best-fit” line (or curve) through your data

Graphing 10. You may be asked to use your graph to draw conclusions & make predictions. Three examples would include: Interpolation – within the limits of the data Extrapolation – beyond the limits of the data Slope Determination (show work on graph)

“Best-Fit” Line Distance vs. Time for Freefall

Temperature of Water Graph Construct a graph of the data that was collected. o F on the y-axis o C on the x-axis Draw best-fit line through data points. Calculate the slope of the line and show your calculations on the graph. Use the slope and the y-intercept to write the equation of the line (y = mx + b). What does this equation represent? What is the 0 C that is equivalent to 0 o F (determine this by using the graph itself)? What graphing technique did you use to determine this?

Dimensional Analysis A simple mathematical approach to converting between units. Involves conversion factors (fractions). Follows simple math functions (x/÷) We can use conversion factors for metric conversions as well as other conversions. Dim. analysis can be used to convert from 1 unit to another. One step or several steps. Each conversion factor represents a math function – treat it as such.

Dimensional Analysis Examples: 1. What is the volume of a 250-mL beaker in L? 2. What is your weight in g? 3. How many kg are equivalent to 4 lbs? 4. How many mg are in.500 lbs? 5. How many lbs are equivalent to 4.00 kg?

Density Density is a property of matter representing the mass per unit volume For equal volumes, denser object has larger mass For equal masses, denser object has small volume Solids = g/cm 3 1 cm 3 = 1 mL Liquids = g/mL Gases = g/L 1L = 1 dm 3 Volume of a solid can be determined by water displacement

Using Density in Calculations Density = Mass Volume Volume = Mass Density

Brownie Graph 1. Graph mass (y) vs. volume (x) 2. Draw best-fit straight line through data points. Extend to y-axis 3. Calculate slope (decimal # and units) – show work on graph 4. Answer the following: - What does the value for the slope represent? - What is the value for the y – intercept? - What does it represent?