1. Unit 1 Safety, Measurements, & Dimensional Analysis

2. What is chemistry? The textbook definition of it is “ the study of matter and the changes that it undergoes.” It is sometimes called the central science because every other science requires a basic understanding of chemistry.

3. What is Matter? Everything in the universe is composed of matter. The fuels that keeps your car running, the fuel that keeps YOU running, the materials of which you are made – all are made of matter. Matter is anything that has mass and takes up space. What about air?

4. Characteristics of Matter All matter has mass. Measured in kilograms (kg) Mass does not vary depending on location. Weight is a measurement that includes mass but also takes into account the effect of the earth’s gravitational pull on that matter. For weight, location does matter!

5. Chemistry: the Central Science There are many branches of chemistry covering a wide range of topics: Organic: based on carbon compounds Inorganic: mostly matter that does not contain carbon Physical Chemistry: behavior & energy changes Analytical: components and composition Check out Table 1:1 for more!

6. The Scientific Method Systematic approach to pose and solve and analyze problems. Involves making careful observations. Two kinds of observations: ◦1. Qualitative: using your 5 senses – color, odor, shape, or a physical characteristic ◦2. Quantitative: Numerical from measurements – temperature, mass, volume

7. EXPERIMENTS!!! Set of controlled observations to test the hypothesis. Independent variable: the experimenter Intentionally changes Dependent variable: changes in response to the independent variable

8. Units & Measurements (Ch. 2)

9. Base Units \ SI Prefixes Scientists need a standard for measurements for reporting data that can be interpreted and used by other scientists. Today we use the Systeme Internationale d’Unites or SI for short.

10. Base Units There are 7 “base units” in SI. A base unit is based on an object or event in the physical world and is independent of other units.

11. The base units are QuantityBase unit TimeSecond (s) LengthMeter (m) MassKilogram (kg) TemperatureKelvin (K) Amount of substanceMole (mol) Electric currentAmpere (A) Luminous intensityCandela (cd)

12. SI prefixes that you need to know PrefixSymbolNumerical ValuePower of 10 GigaG1,000,000,00010 9 MegaM1,000,00010 6 KiloK100010 3 -- 110 0 Decid0.110 -1 Centic0.0110 -2 Millim0.00110 -3 Microµ0.000 00110 -6 Nanon0.000 000 00110 -9 Picop0.000 000 000 00110 -12

13. Moving from one unit to another Stairstep

14. The SI unit for time is based on the frequency of the radiation given off by a cesium-133 atom. Many chemical reactions take place in fractions of seconds. A meter is the distance that light travels in a vacuum in 1/299,792,458 th of a second. A kilogram is determined by the mass of a platinum and iridium cylinder in France stored in a vacuum jar to prevent oxidizing. One kg is approximately 2.2 lbs.

15. Temperature Temperature is the average kinetic energy of the particles that make up an object. Temperature is measured with a thermometer or temperature probe. There are three temperature scales commonly used. ◦Fahrenheit Used in USA FP 32 0 BP 212 0 ◦ Celsius Worldwide FP 0 0 BP 100 0 ◦ To convert Celsius to Fahrenheit use this formula ◦ 0 F = 1.8( 0 C) + 32

16. Kelvin is the scale adopted by SI. At 0 Kelvin (don’t use the degree symbol), particles are at their lowest possible energy state. On Kelvin scale water’s FP 273.15 K ◦ BP 373.15 K 0 Kelvin is called absolute zero To convert from Celsius to Kelvin use this formula K = 0 C + 273

17. Derived Units Any unit made by combining 2 or more base units is a derived unit. Examples are ◦speed distance / time m/s or mi/hr (mph) ◦Volume cm 3 ◦ density = mass = g or g  volume cm 3 ml  If you are given the mass and density, how would you determine the volume? Practice pg 39

18. Volume can be measured in multiple ways. 1Liter =1 dm 3 and 1 ml = 1 cm 3 1 liter is about the same as 1 quart.

19. Scientific Notation and Dimensional Analysis pgs 40-46 In science we often use very large numbers such as the number of atoms in a given amount of substance. ◦Ex. 460,000,000,000,000,000,000,000 atoms of carbon in the Hope Diamond Other times we use very small numbers such as the mass of a single atom. O.00000000000000000000002 g in one carbon atom

20. All those zeroes just get in the way! We can express those numbers in scientific notation without changing their value. To do that we write the number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent). ◦Ex. # atoms in Hope Diamond = 4.6 x 10 23 ◦ Mass of one carbon atom = 2 x 10 -23 g ◦ Practice pg 41

21. Working problems in “sci not” Addition\Subtraction ◦Exponents must be the same Multiplication Multiply the coefficients, then ADD exponents Division Divide the coefficients, then SUBTRACT exponents Practice pg 42 & 43

22. Accuracy & Precision Measurements contain uncertainties that affect how a calculated result is presented. ◦Some relate to the device used ◦Some to human skill

23. Accuracy refers to how close a measured value is to the accepted value. ◦Ex. A brand new nickel has a mass of exactly 5 g ◦Class activity

24. Error & Percent Error When working in a lab situation, we should check ourselves for error. Error = experimental value – accepted value If you measured the mass of a brand new nickel as 4.95g, your error would be 4.95g – 5.00g = - 0.05g

25. A more useful tool is percent error. Percent error = [ error ] x 100 accepted value [error] is the absolute error which is always positive Percent error is a measure of accuracy. In any lab where your percent error is ≥ 10%, you should always include an explanation of why your error is that large. Practice pg 49

26. Precision refers to how close a series of measurements are to one another. Precision can be determined by calculating the uncertainty of a set of measurements.

27. To determine uncertainty 1. find the average of the measurements 2. for each measurement, find the absolute deviation from the average. 3. average the deviations 4. report using ± symbol

28. Example Uncertainty Example Uncertainty How old is Coach Thompson? If 5 people guess 63, 59, 60, 61, 61 Average = 60.8 Deviations from 60.8: 2.2, 1.8, 1.8,0.2,0.2 Average deviations = 1.04 Report answer as 60.8 ± 1.04 Is this accurate? You would have to ask Coach!

29. Significant Figures Often precision is limited by the tools available. ◦Ex. A digital clock can only read to what is displayed on the dial ◦BUT a stopwatch can record to the nearest hundredths of a second. Limitations also can come from the condition of the tool AND the skill of the person using it.

30. The precision of a measurement is indicated by the number of digits reported. 4.75cm is more precise than 4.7cm Significant figures- include all known digits plus one estimated digit.

31. Recognizing Sig Figs The Five Rules: 1. Nonzero numbers are ALWAYS significant. 33.56 g 2. Zeros between nonzero numbers are ALWAYS significant. 989.08 cm 3. All final zeros to the right of a decimal ARE significant. 8.50 ml 4. Placeholder zeros are NOT significant. 0.055 ml or 78600 m 5. Counting numbers and defined constants have an infinite number of significant figures. 5 moles 60 s = 1 min

32. Practice pg 51

33. To round or not to round… Reporting data with significant figures ◦Reported values should have the correct number of sig figs. ◦That is, no more than the original data with the FEWEST sig figs. ◦Often you will need to round. ◦First, decide the correct number of sig figs.

34. Practice pg 53 Rounding rules pg 52 1. if digit to right of the last sig fig is < 5, do not round up. 2. if digit to right of last sig fig is > 5, round up! 3. if digit to right of last sig fig is 5 followed by a nonzero digit, round up. 4. if digits to the right of the last sig fig are a 5 followed by a 0 or no other number, if last sig fig is odd, round up. If last sig fig is even, do NOT round up.

35. Dimensional Analysis It’s a systematic process of solving problems using conversion factors. Referred to as the factor-label method. Conversion Factor: a ratio of equivalent values with different units. ◦Ex. 1 foot = 12 inches ◦ 1 day = 24 hours ◦ 1 meter = 100 cm

36. Writing Conversion Factors One set of equivalents. 1 ft = 12 in Two ways to write a conversion factor. 1 ft or 12 in 12 in 1 ft What’s the purpose? Trying to lose (cancel) one unit and (introduce) go to another one. Practice pg 45

37. PIZZA PARTY TIME! ____ people, 3 slices per person, 8 slices per pizza…. How many pizzas do you need to order? If the pizzas cost $6 each, how much money do you need to pay for them?

38. Presenting Data – tables & graphs Graphing pgs 55 – 57 In science we are interested in analyzing our data for trends or patterns. Does raising the temperature change the reaction rate. How much chemical is needed to change the boiling point by a certain number of degrees. Using graphs can help us answer those questions.

39. Circle graphs, pie charts – useful for showing parts of a whole. Often used when data is presented in percentages.

40. Bar Graphs – often used to show how a quantity varies across categories such as time, location, and temperature. The quantity being measured is shown on the vertical (y) axis. The independent variable appears on the horizontal (x) axis.

41. In Chemistry, most of our graphs will be line graphs. The points on the line represent the intersection of data for two variables. Independent variable is plotted on the x- axis. Dependent variable on the y-axis. To establish a trend, we do NOT “connect the dots” but draw a best-fit line. Best-fit lines will have about as many points above the line as below it.

42. IF the best-fit line is straight, the relationship between the two variables is said to be “linear” and the variables are directly related. The slope of the line rises to the right, it is positive. (as x increases, y increases) If the slope sinks to the right, slope is negative. (As x increases, y decreases)

43. Calculating slope: ◦With 2 pairs of data points, you can calculate the slope of the line. ◦Slope = rise = ∆y = y 2 - y 1 ◦ run ∆x x 2 - x 1 ∆ means “change in”

44. Interpreting Graphs Use a systematic approach to analyzing graphs. 1. note the dependent and independent variables. 2. x-axis values depend on y-axis values 3. is it linear or nonlinear? 4. if linear, is it positive or negative?

45. 5. If points are connected, it is continuous so you can read the values between points (interpolation)

46. 6. you can also extend the line beyond given points to estimate values – (extrapolation)