Intro to Chemistry, the Scientific Method, and Measurement

Transcription

1 Intro to Chemistry, the Scientific Method, and Measurement

2 Why Study Chemistry? Produce new materials New sources of energy Medicine Criminal investigations Weapons

3 Learning Chemistry Fair amount of memorizing Learn the core curriculum Problem Solving Get information out of the text

4 What is Chemistry? The science that deals with the materials of the universe and the changes that these materials undergo Sometimes called the central science most phenomena in the world involve chemical changes Photosynthesis & respiration Combustion Food production Memory storage Looks at the microscopic world molecules and atoms

5 Review 1. What are some reasons to study chemistry? 2. What is chemistry? 3. What are some places in the real world where chemistry is used?

6 The Scientific Method 1. Question (or problem) - What is the main topic of your exploration? 2. Research - In this step, you find out what everybody else knows about your topic already. - You need to look at credible sources to find this information. - Try to find out something about your topic that nobody knows the answer to, or at least something that you do not know the answer to.

7 The Scientific Method 3. Hypothesis - A possible explanation of events or a possible answer to your question. - it needs to be based on your research. - There are two types of hypotheses: - Null Hypothesis (H 0 ), which states that there will be no difference between the control group and the experiment group. In other words, nothing will happen. (more professional) - Alternate Hypothesis (H A ), which is your prediction of what will happen in the experiment. (common)

8 The Scientific Method 4. Experiment - You need to briefly list your materials and methods. - You need to write out the steps you will take to perform your experiment. - All experiments must be divided up into two groups: experiment and control. - In the experiment group, you add different variables (one at a time) to see how they alter the experiment (called independent variables). Besides the different variables in each test, EVERYTHING ELSE MUST BE THE SAME! - In the control group, you perform the same experiment, but you add no variables. The result here is what you compare everything else to. - You must record your results. These results must be measurable. The things you measure are called dependent variables. Generally, you only measure one dependent variable per experiment.

9 The Scientific Method 5. Record and Analyze Data - Make sure to keep good records of your results. - Put your data into a table, graph, chart, etc. so you can compare your results easily. - If you get serious, you need to analyze your data using a statistical test st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North

10 The Scientific Method 6. Conclusion - Must refer back to your hypothesis. - If you used an alternate hypothesis, you either say that your hypothesis was right, or it was wrong. - If you used a null hypothesis, you need to say that you either proved your hypothesis wrong, or you failed to prove your hypothesis wrong (it was right). 7. Retest / Application / Publish Results - In this section, mention any questions that you came up with because of your experiment, anything you did wrong, etc. - Also, mention why anyone should care about your results (you MUST care) and how they could apply them to their lives.

11 Review 1. What are the steps of the scientific method? 2. What are the two types of hypotheses and when might you use each one? 3. Why should you do research? 4. What is a control group and what is it used for? 5. What is an independent variable? 6. Why should you use tables and graphs? 7. Why should you retest?

12 Fact vs. Inference Fact: a thing that has already happened or is thought to be true Infer: to derive or conclude by reasoning from something known or assumed Examples: There is a tree in the picture The tree is tall There are three wolves The wolves are hungry The wolves are picky eaters The wolves are holding a paper The wolves are going to help natural selection move along quicker Water Buffalo

13 Facts and Inferences?

14 Venn Diagram Assignment

15 Metric System Le Systemé International (official name) Abbreviated as SI system Also called the metric system in US (unofficial name) Official system of measurement in every major country in the world but one.

16 III. Units of Measurement Everything based on the meter Today s definition of a meter The distance that light travels in a very small amount of time in a vacuum (in 1 / 299,792,458 sec) This is a good definition because the speed of light never changes (c = 3 x 10 8 m/s) French scientists created a set of prefixes that multiplied or divided the meter by fractions of 10 to make smaller and greater units of measurement

17 Prefixes Prefix Abbreviation How it Equates Tera..T. 1 Tm = 1,000,000,000,000 m Giga.G.1 Gm = 1,000,000,000 m Mega..M.1 Mm =1,000,000 m Kilo..k....1 km = 1,000 m Hecto.h. 1 hm = 100 m Deka.da. 1 dam = 10 m Basic Unit (Meter, Liter, Gram)..m, L, g... 1 m = 1 m deci...d..1 dm = 0.1 m centi.. c....1 cm = 0.01 m milli m...1 mm = m micro....µ µm = m nano. n..1nm = m pico p....1pm = m

18 Energy Joule J

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20 IV. Uncertainty in Measurement Precision: Measurements are close to one another Accuracy: Measurements are close to accepted value

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22 V. Working with Numbers Significant Digits : refers to all certain numbers in a measurement and one estimated number All measurements must include a number and the unit in which it was measured

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25 Significant Figures 1. All nonzero digits are significant Zeroes between two significant figures are themselves significant Zeroes at the beginning of a number are never significant Zeroes at the end of a number are significant if a decimal point is written in the number

26 Significant Figures When addition or subtraction is performed, answers are rounded to the least significant decimal place =???? When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation. 3 x 2.2 =????

27 Scientific Notation Makes small and large numbers easier to work with Two parts 1. Change to a number between 1 & Use a power of ten for decimal movement Turns 1200 to 1.2 x 10 3 What would turn to????

28 Percents and Percent Error % = amount have x 100 amount possible 8 people out of 10 are here today. What percent is that? % error= measured value accepted accepted value x100 Boiling point is 100 C. You measure it at 98 C. What is your percent error?

29 Ratios in Calculations Speed = length time Density = mass volume

30 VI. Problem Solving Dimensional Analysis: Technique for converting between units Unit equality: tells how units are related (see pg. 130) Conversion factors: a unit equality written as a fraction

31 Example: Change 250 gals into Liters Step 1: Find a unit equality 1 gal = L Step 2: Write conversion factors 1 gal/ L L/ 1 gal Step 3: Choose correct conversion factor -cancel units

32 Step 4: Solve 250 gals x L = 950 L 1 gal 5 inches =??? Centimeters 10 meters =??? kilometers

33 Lengthy Conversions: Change 5.0 hours into seconds Step 1: 1hr. = 60 min. 1 min. = 60 s Step 2: 60 min./ 1 hr. 1 hr./ 60 min. 1 min./ 60 s 60 s/ 1 min. Step 3 & 4: 5.0 hr. x 60 min. x 60 s = 18,000 s 1 hr. 1 min.

34 Two variables are compared 1. independent variable scientist changes (x-axis) 2. dependent variable responds to changes in the other variable (yaxis) Graphing

35 Steps to making a graph Label axes of graph name of variable & units Determine the scale on each axis and label Plot measurements Connect data points with best fit line Title graph should describe graph

36 Review 1. What is the official name for the metric system? 2. What unit is everything in the SI system based on? 3. What prefix means 10? 4. What prefix means 0.01? 5. What unit is used to measure volume? 6. What unit is used to measure mass? 7. What unit is used to measure energy?