Pre AP ChemistryUnit 1Chapters 1 & 2 Introduction to Chemistry Scientific Method and Analyzing Data
What is Chemistry? • It is the study of matter, energy and the changes they undergo. • It is central to the understanding of all other sciences. • What is matter? It is anything that has mass and takes up space. • What is mass? A measurement that reflects the amount of matter. Moles do also but deals with numbers of things.
Mass vs. Weight • Weight is a measure of the amount of matter and how the Earth’s gravitational field pulls on the matter. • Which one changes with location? • What units is mass measured in? • What units is weight measured in? • What apparatus is mass measured with? • What apparatus is weight measured with?
Scientific Method • Systematic approach used in scientific study to avoid bias • Steps (can vary, no set #) 1. Define or recognize a problem or question or observation 2. Form a hypothesis – an explanation or educated guess 3. Test the hypothesis with an experiment – set of controlled observations that is carefully planned and has a detailed procedure 4. Analyze the data collected 5. Form a conclusion – judgment based on information obtained • Does it support or refute the hypothesis? • Does the hypothesis need to be revised?
Bellringer in notes • Concept Assessment: • True or False: The Scientific Method is a linear process with a discrete start and end. • True or False: An experiment can prove a hypothesis. Why? • What is the difference between a law and a theory? • _____ is measured with a scale. • ____ is measured with a balance. • Mass is measured in _______________. • Weight is measured in _____________. (metric system!) • The measurements you take in an experiment are the _______ variables.
Independent variable – the condition that the experimenter changes (manipulates) Dependent variable – the value that changes (responds) because of the independent variable Constants – conditions for all subjects that are kept the same Control – standard to compare results to, does not have the variable to be tested • Qualitative data – describes physical characteristics • Quantitative data – numerical information
Terms to know • Model – a visual, verbal, or mathematical explanation of experimental data • Theory – hypothesis (explanation) that has been supported by many experiments • Hypotheses must be testable • Scientific law – hypothesis in nature that has been supported by many experiments and has not been contradicted. • Unlike a theory, a law is a statement not an explanation. For example, the Law of Gravity states what gravity does, it does not attempt to explain it. A common misconception is that theories can eventually become laws, but this is not true – one is an explanation, one is a statement.
HW Experimental design • Experimental design assignment • Design your own experiment, give it a corny title… • Tell how, where, what, etc. • This is a combination creative writing and lab report, you can write it in paragraph form or a lab report form. Make up a good experiment and tell what you ”did”. • Discuss also: • Control • Constants (5 minimum) • IV • DV • Results and Conclusion • Due Friday Aug 21 • Consumer lab will be on Aug 28, your group will need to be ready then.
Consumer Product Survey Lab • Work with a partner • Choose a product to test, ex. 3 types of hot dogs or 4 different pens • Eliminate bias as much as possible • Be creative and think things through, get your logistics on. • You will need to purchase plates or cups, the product, a palate cleanser, napkins, etc. • Survey Science classes on Aug 28 • Gather + analyze data, you will write a lab report and present your data to the class
Branches of Chemistry • Organic most carbon compounds • Inorganic non-carbon compounds and organometallic cpds • Physical matter and energy interchange • Analytical composition of materials • Biochemistry substances and processes in living systems • Theoretical math + computers to design and predict behavior of substances and processes
Bellringer • Which branch of chemistry studies molecules with carbon? • What is the difference between a theory and a law? • What is the dependent variable? • Which goes on the horizontal axis? • What is a control?
Data Analysis • Manipulating and analyzing numbers
Graphs • There are 3 basics types of graphs. • Bar Graphs • Used to compare a set of measurements, amounts, or changes
Graphs (cont) • Circle Graphs (Pie Graphs) • Shows how a part of something relates to the whole – shows percentages
Graphs (cont) • Line Graphs - shows changes that occur in the related variables • Independent variable is plotted on the x-axis • Dependent variable is plotted on the y-axis • Slope of the line represents the relationship between the 2 variables • Slope = y2 – y1 x2 – x1 • Slope can be a direct proportion – the variables both increase or both decrease • Slope can be an inverse proportion – one variable increases and the other decreases or vice versa
Guidelines for Making Graphs • Always divide the axes into even units • You do not have to start with zero • You can use different divisions on the x- and y-axis • Choose your divisions to make a large graph • Always give your graph a title • Always label both axes with the measurement as well as the unit it was measured in. The unit goes into parenthesis. • Connect the data points – many times this will be with a best fit straight line
Significant Figures and numbers Still in Unit 2: Sci Method and Data Analysis CHEM IS TRY
Significant figures (or digits)these indicate how good a measurement is. • How many sig figs?
More • How many sig figs? Meniscus
Homework • Experimental design due Fri Aug 21 • Think about Consumer Lab on Fri Aug 28
Try these A B C A = ________________ B = ________________ C = ________________
Here's a little story that may help you understand the idea behind significant digits: • Some tourists at the Museum of Natural History are marveling at the dinosaur bones. One of them asks the guard, “Can you tell me how old these bonds are?” • The guard replies, “They’re three million, four years and six months old.” • “That’s an awfully exact number,” says the tourist. “How do you know their age so precisely?” • The guard answers, “Well, the dinosaur bones were three million years old when I started working here, and that was four and a half years ago.”
Being careless with significant figures may result in dire consequences. The following is a true story told to me by a Baltimore County middle school teacher concerning their mishap resulting from not considering the significance of significant figures: • The science teachers at a Baltimore County middle school wished to acquire a steel cube, one cubic centimeter in size to use as a visual aid to teach the metric system. The machine shop they contacted sent them a work order with instructions to draw the cube and specify its dimensions. On the work order, the science supervisor drew a cube and specified each side to be 1.000 cm. • The science supervisor, not thinking about the "logistics", verified this number. When the finished cube arrived approximately one month later, it appeared to be a work of art. The sides were mirror smooth and the edges razor sharp. When they looked at the "bottom line", they were shocked to see that the cost was……….
……….. $500! Thinking an error was made in billing, they contacted the machine shop to ask if the bill was really $5.00, and not $500. At this time, the machine shop verified that the cube was to be made to four significant figure specifications. It was explained to the school, that in order to make a cube of such a high degree of certainty, in addition to using an expensive alloy with a low coefficient of expansion, many man hours were needed to make the cube. The cube had to be ground down, and measured with calipers to within a certain tolerance.. • So, "parts and labor" to prepare the cube cost $500. The science budget for the school was wiped out for the entire year. This school now has a steel cube worth its weight in gold, because it is a very certain cubic centimeter in size. http://pages.towson.edu/ladon/sigfigs.html
Rules and more rules… • In a measurement, includes all known digits plus one estimated digit • Rule 1: Digits other than zero are always significant • Rule 2: Zeros to the right of number AND right of decimal are significant • Rule 3: Zeroes between two other significant digits are always significant • Rule 4: Zeroes used solely for spacing the decimal point are not significant • Rule 5: Counting numbers and defined constantshave an infinite amount of significant figures
Examples… tell how many sig figs • 1400 • 27.00 • 0.0133 • 0.00520 • 1,000 • 3,030
Bellringer • Tell how many sig figs are in these measurements. • A) 10.0 cm b) 0.00349 cmc) 2.35 cm d) 0.02 cm e) 4.430 cm • ‘If these were all taken with a lab ruler, evaluate the correctness of each.
Bellringer • Correct each of the following: • Mia Nottabrane measured her chemistry textbook with a std ruler: 3.320 cm x 34.55 cm x 0.00382 cm • 12, 340, 000 = 5 sig figs • The area of a carpet is 6.5 m3 • Sylvester measured the mass of Tweety bird to be 0.459 kg with a scale from the chem lab. • Weight is measured in Newtons in the English system using a scale that has springs.
Addition and Subtraction • Your answer must have the same number of digits to the right of the decimal point as the value with the fewest digits to the right of the decimal point. Round to get this amount. • Must be in the same power. • If not, must change to same power or to a regular number, keep the same power of 10. • Answer must have same places past decimal as least of the original numbers. • Check to make sure answer is in correct scientific notation.
Adding and Subtractingleast number of places past decimal • Ex. 1.059 g + 0.23975 g = • 45 mL - 13.84 mL = • Ex. 2.849 - 0.3971 • 2.93 x 10 3 + 4.92406 x 10 6
Multiplying and Dividing • Your answer must have the same number of significant figures as the measurement with the fewest sig figs • Multiply the factors and then add the powers of 10 • Ex. 3.00 x 10 4 x 4.0 x 10 3 • Divide the factors and then subtract the powers of 10 • Ex. 3.00 x 10 4 x 4.0 x 10 3 • Ex. 450.3 / 23 = • 0.0238 m x 0.0289309 m =
Tutorials • http://misterguch.brinkster.net/sigfigs.html tutorial • https://www.youtube.com/watch?v=VAuslY-Uuf4 Tyler deWitt 7 min • http://www.proprofs.com/quiz-school/story.php?title=significant-digits-rounding quiz • http://www.funbrain.com/measure/
Scientific Notation • It expresses numbers as a multiple of 2 factors • A number between 1 and 9 • Ten raised to a power (exponent) • We use it in science to easily deal with both small and large numbers. • To convert scientific notation to normal numbers, move the decimal point “n” times • positive to the right, negative to the left • Ex 17,300,000 and 0.000 023
Steps • Move the decimal point to produce a factor between 1 and 9. • Count the number of spaces you moved and note which direction. • Remove the extra zeroes at the end or beginning unless the zero is the last number and it is after the decimal point. • Multiply the result by 10n where n=# of places moved • n is positive if the decimal point was moved to the left (the # got smaller) • n is negative if the decimal point was moved to the right (the # got bigger)
Scientific NotationIs a Coefficient raised to power of 10 (ex 6.9 x 10-3)Practice Problems: • 80 = 0.0000070 = 8 X 101 7.0 X10-6 • 268 = 2.4 X 104 = 2.68 X 102 24000 • 247.89 = 3.8 X 10-4 = 2.4789 X 102 0.00038
Practice • 0.00359 = • 45.08 = • 0.034 = • 30.0 = • 2.4 x 103 • 9.8 x 10-2 • 5.0 x 101
Working with Scientific Notation Multiplication • Multiply the coefficients, add the exponents • (3.0 x 104) x (2.0 x 102) = Division • Divide the coefficients, subtract the denominator exponent from numerator exponent • 3.0 x 104 2.0 x 102 = 6.0 x 106 1.5 x 102
Assessing Measurements • Precision – how close a set of measurements are to each other, regardless if correct or not • Accuracy – how close a measurement is to the true or accepted value (TV) 34.94, 30.28, 29.04 ? TV = 26.072 5.595, 5.592, 5.602 ? TV = 5.988
Percent error • Percent error = |your value – accepted value| x 100 accepted value • What does the |your value – accepted value| mean?
Bellringer • Today will be graded • You have 3-4 min to look over notes. Precision vs accuracy How many sig figs in a number How to put numbers in sci notation Answer in correct sig/figs: Add/subtract Answer in correct sig/figs: Mult/div Rounding numbers
Things to work on after the quiz • Finish Lab “Who do you think you are” • Finish questions and % error • Make-up for late points: Pg 96 # 58-61, 79 and pg 96 # 63, 64, 70 • Turn in one sheet of paper: Consumer lab pre-experiment (names of group members, period, what you are doing and how, how are you reducing bias (be specific), how are you going to hide the product, who is bringing what, what ballot look like (give me a sample if you want copies), etc.)
Measurement systems Metric system • Developed before the French Revolution (~1790) • Antoine Lavoisier • Based on units of 10 (uses prefixes) • Used by all major countries except US SI (International system) • ~1960, chooses some metric units to be an international standard • 7 base units • kg, s, m, K, etc. CGS • Used in laboratory for ease of recording • cm, gram, s https://www.youtube.com/watch?v=MekxJse2vgs Bill Nye metric system https://www.youtube.com/watch?v=WuaxXcgX6Rc Causey
Videos • https://www.youtube.com/watch?v=GZ0BpiCm6cYstddev metric system
Metric Conversions • kentuckyhas dark anddirty coal mines • M x x k h da+ d c m x xμ x x n • Mega; kilo; hecto; deka; “AND” is BASE UNIT (g, L, m); deci; centi; milli; micro, nano • Note: “m” means “meter” when it is a UNIT but means “milli” when it is a PREFIX • Ex. Convert 45 m (meters) to mm (millimeters) • How many micrograms are in 0.00621 cg? • Convert 3.06 L to mL
JFF • 10 -2pede = a _______________ • 10 6 phones = a _________________ • 10 rations = a ________________ • Who do you go to for legal help? the 10 -18 rney = ___________________ • My favorite Mexican salsa? 10 -12 de gallo = _____________________