Chemistry Introduction: Matter, Variables, and Scientific Method

1. Chapter One INTRODUCTION TO CHEMISTRY

2. Monday Scientific method foldable Variables foldable Variables worksheet for homework

3. Section 1.2 Chemistry and Matter • Chemistry- Study of matter and changes it undergoes • Matter- anything that has mass and takes up space

4. What’s the difference between mass and weight???

5. Mass- the amount of matter in an object • Weight- measure of matter and effect of gravity on an object

6. What do the prefixes macro- and micro- mean???

7. Macroscopic- do not need a microscope to see it • Submicroscopic- so tiny that parts can’t even be seen with microscope (ex: atom)

8. Submicroscopic events are explained by making models (a visual, verbal, or mathematical explanation of how things occur)

9. Section 1.3Scientific Methods Scientific Method- a systematic approach used in all scientific study

10. Steps of Scientific Method 1. Observation- the act of gathering information; may be qualitative data (from 5 senses) or quantitative data (numerical information)

11. 2. Formulate hypothesis (testable statement or prediction about what has been observed)

12. 3. Conduct Experiment (set of controlled observations that test hypothesis)

13. Variables Independent and Dependent Variables: What they mean and how to use them

14. What is a variable? In the design of a scientific experiment, a variable is any factor that changes from data group to data group. Scientific experiments are designed so that the tested variables are the only things that are supposed to change from group to group; all other factors are to remain constant

15. A handy Mnemonic for Variables Remember this phrase: DRY MIX

16. Dependent Variable Dependent Variable is the variable that Responds to the experimental design and is graphed on the Y-axis

17. Independent Variable The variableManipulated by the scientist is called theIndependent variable and is graphed on the X-axis

18. Constant – variable that does not change during an experiment Control- standard for comparison

19. For Example: John wants to test how outside temperature effects pea plant growth. He sets up four identical greenhouse boxes where the only difference in the plant environments will be ambient temperature. One plant will grow at 10 °C. Another will grow at 20 °C which is room temperature. A third will grow at 30 °C. Finally, a forth will grow at 50 °C. After 30 days, the pea plants were measured for growth.

20. Data Table

21. Graph

22. 4. Analyze the data (more to come in chapter 2)

23. 5. Form a conclusion (judgment based on the information obtained; comparison of hypothesis with actual results)

24. Theory- explanation supported by many, many experiments Ex: Big Bang Theory Scientific Law-when the same conclusion is found many times with no exceptions Ex: Newton’s Law of Motion

25. Scientific Method and Law

26. Discussion Which variable was the independent variable? Which variable was the dependent variable? Which plant represented the control group?

27. Tuesday Correct variables worksheet Scientific notation Significant figures Accuracy and precision

28. Chapter 2 Data Analysis

29. 2.1 Units of Measurement • In 1960 the metric system was updated and is called the SystemeInternationaled’Unites or the SI unit of measurement. • Standard units of measurement for ALL scientists to use worldwide.

30. Base Unit - unit of measurement based on an object or event in the physical world The standard kilogram is stored in a vault at the International Bureau of Weights and Standards near Paris. It is made of a platinum-iridium alloy, and is shown here next to an inch-based ruler for scale.

31. Base Units: 1. Time: second (s) 2. Length: meter (m) 3. Mass: gram (g)

32. 4. Temperature: Kelvin (K) 5. Amount of substance: mole (mol) an international standard to measure an "amount of stuff" aka Mole! It refers to the number of atoms in 12 grams of carbon 12 (6.022 x 1023) Avagadro’s Number

33. Derived Unit - A unit that is a combination of base units. • There are hundreds of units needed for measuring “everything,” but they are all derived from those base units.

34. Volume = L x W x H for a regularly shaped solid cubic meter (m3),cubic centimeter (cm3) or cubic decimeter (dm3) • Unit for volume: liter (L) for a liquid • 1 dm3 = 1 L 1 cm3 = 1 mL

35. Density- ratio that compares the mass of an object to its volume • Units are grams per cubic centimeter (g/cm3) • 1 ml = 1 cm3

36. density = mass volume Density is a property that can be used to identify an unknown sample of matter.

37. Temperature • Kelvin – SI base unit for temperature • ºC + 273 = K • K – 273 = ºC • There are no negative temperatures in Kelvin

38. 2.2 Scientific Notation • Scientific Notation- expresses numbers as a multiple of two factors: 1. A number between 1 and 9 2. Ten is raised to a power (exponent). • 2.0 x 103 3 is the exponent • 2.0 x 103 = 2000 • .20 or 20 would be WRONG because they are NOT numbers between 1 and 10!!

39. Scientific Notation Example Count the number of places the decimal point moved and the direction • Convert 436289 to scientific notation. • Place decimal at end of number 436289. • Move decimal to place it behind the first number 4.36289 • Youmoved the decimal 5 places left.  • If decimal moves left, the exponent is positive • The # of times the decimal was moved becomes the exponent. 4.36289 x 105

40. If decimal moves left, exponent is positive • if decimal moves right, exponent is negative

41. Convert .000872 to scientific notation • Move the decimal behind first number that is NOT a zero. 0008.72 • 8.72 You moved the decimal 4 places right.  • The # of times the decimal was moved becomes the exponent. • If decimal moves right, exponent is negative. • The # of times the decimal was moved becomes the negative exponent • 8.72 x 10 – 4

42. To convert Scientific Notation to Standard Notation Reverse the above steps: • If the exponent is positive move the decimal to the right the same number of places as the exponent. • 2.5 x 104 = 25 000 • If the exponent is negative move the decimal to the left the same number of places as the exponent. • 2.5 x 10-4 = .00025

43. Adding, subtracting, multiplying, and dividing in Scientific Notation by using the calculator • Use “EE” or “exp” key on your calculator to replace “ x 10^” • Ex: 8.72 x 10-4 would be 8.72”EE”-4

44. Sect. 2.3: How reliable are measurements? • Accuracy– how close a measured value is to an accepted or true value • Precision – how close a series of measurements are to each other • Compare to throwing darts bottom of pg 36.

46. ACCURACY VS. PRECISION: HOWEVER, if the actual time is 3:00, then the second clock is more accurate than the first one. • ACCURACY = HOW CLOSE A MEASUREMENT IS TO THE TRUE VALUE • PRECISION = EXACTNESS THIS CLOCK is more precise than THIS CLOCK

47. Percent error– the ratio of an error to an accepted value. % error = experimental – accepted x 100 accepted value Example: Density of lead is 11.3, you had 10.3 in your experiment. Difference is 1 So 1 x 100 = 8.8% 11.3

48. Significant Figures • Accuracy is limited by the available tools. • Sig figs are based on instrument precision (numbers can only be as exact as the instrument is) • Instruments must be calibrated to assure accuracy.

49. The “best” number is the one with the most decimal places. • So 3.54 g is MORE precise than 3.5 g. Significant figures - include all known digits plus ONE estimated digit.

50. Having Trouble with Sig Figs? Try this: 1. Determine if the decimal point is “present” or “absent”. 2. Picture a map of the U.S. with the Pacific Ocean on the left and the Atlantic Ocean on the right. PACIFIC ATLANTIC Decimal present Decimal absent   3. If the decimal point is “present”, imagine an arrow LEFT from the Pacific Ocean pointing to the number. (Think “P” for “present” and “Pacific”).  4. If the decimal point is “absent”, imagine an arrow RIGHT from the Atlantic Ocean pointing to the number (“A” for “absent” and “Atlantic”).  5. Start counting digits when the arrow hits a non-zero digit. Each digit after that is significant.