Safety MSDS Scientific Method Powers of 10 Accuracy vs. Precision Significant Digits Dimensional Analysis

What is Chemistry? Chemistry is the study of matter and the changes it undergoes. It is a science of inquiry. We need chemistry to understand medications, cooking, and transportation issues.

Reasons to Understand Chemistry Be a better informed citizen so that you understand news stories about chemicals. So that you understand drug and chemical interactions and can make better choices about your life.

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MSDS

The Most Misunderstood Words in Science Hypothesis, theory, skeptic, model, nature vs. nurture, significant, natural

Observation Hypothesis Experiments Conclusion –Model –Theory –Law

Theory vs. Law Scientific theories explain why something happens. As technology changes, theories can be improved. Scientific laws explain how something happens. Laws don’t change.

Inference vs. Observation Observations are made using your senses. Inferences are made by comparing past experiences.

Hypothesis vs. Theory Hypothesis –Explanation of why something happens that must be testable. –Requires extensive testing after which it may become a theory. Theory –Explanation of why something happens that has been tested many times, is well established, and highly reliable

Models We used models to explain hypotheses. What are some kinds of models that you know?

Pure Research –Research for the sake of knowledge Applied Research –Solve a specific problem –Includes technology

Standards of Measurement When we measure, we use a measuring tool to compare some dimension of an object to a standard. For example, at one time the standard for length was the king’s foot. What are some problems with this standard?

SI measurement Le Système international d'unitésLe Système international d'unités The only countries that have not officially adopted SI are Liberia (in western Africa) and Myanmar (a.k.a. Burma, in SE Asia), but now these are reportedly using metric regularlyThe only countries that have not officially adopted SI are Liberia (in western Africa) and Myanmar (a.k.a. Burma, in SE Asia), but now these are reportedly using metric regularly Metrication is a process that does not happen all at once, but is rather a process that happens over time.Metrication is a process that does not happen all at once, but is rather a process that happens over time. Among countries with non-metric usage, the U.S. is the only country significantly holding out.The U.S. officially adopted SI in 1866.Among countries with non-metric usage, the U.S. is the only country significantly holding out. The U.S. officially adopted SI in 1866.

15 The Base SI Units QuantityBase Unit LengthMeter (m) MassKilogram (kg) TimeSecond (s) TemperatureKelvin (K) AmountMole (mol) Electric CurrentAmpere (A) Luminous IntensityCandela (cd)

Derived Units Two or more base units combined mathematically. 1. Volume v = length x width x height volume = meters x meters x meters volume = meters x meters x meters Three base unitsThree base units 2. Density D = mass/volume Density = kilograms/meters x meters x metersDensity = kilograms/meters x meters x meters Four base unitsFour base units 3. Speed s = distance/time Speed = meters/secondsSpeed = meters/seconds Two base unitsTwo base units

Measuring Volume

Volume Remember to read the volume at the bottom of the meniscus!

Powers of 10 See what powers of 10 look like on the above video! Or explore it on your own with this website:

SI Prefixes PrefixSymbolFactorScientific Notation Example GigaG1,000,000, Gigameter (Gm) MegaM1,000, Megagram (Mg) Kilok1, Kilometer (km) Decid1/ Deciliter (dL) Centic1/ Centimeter (cm) Millim1/ Milligram (mg) Microµ1/1,000, Microgram (µg) Nanon1/1,000,000, Nanosecond (ns) picop1/1,000,000,000, Picometer (pm)

Metric Prefixes

Chemistry In Action On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mars’ atmosphere 100 km lower than planned and was destroyed by heat. 1 lb = 1 N 1 lb = 4.45 N “ This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.”

What is Scientific Notation? Scientific notation is a way of expressing really big numbers or really small numbers.Scientific notation is a way of expressing really big numbers or really small numbers. For very large and very small numbers, scientific notation is more concise.For very large and very small numbers, scientific notation is more concise.

To change standard form to scientific notation… Put one non-zero digit to the left of the decimal point.Put one non-zero digit to the left of the decimal point. Count the number of decimal places the decimal point “moved” from the original number. This will be the exponent on the 10.Count the number of decimal places the decimal point “moved” from the original number. This will be the exponent on the 10. If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.

Examples 1.Given: 289,800,000 2.Move: (moved 8 places) 3.Answer: x Given: Move: 5.67 (moved 4 places) 3.Answer: 5.67 x 10 -4

Examples 16. Express the following in scientific notation. a.700 m b.38,000 m c. 4,500,000 m d. 685,000,000,000 m e kg f kg g kg h kg

Examples Solve the following problems on your calculator: a.5 x m + 2 x m b.7 x 10 8 m – 4 x 10 8 m c.4.39 x 10 5 kg – 2.8 x 10 4 kg d.5.36 x kg – 7.40 x kg e.(4 x 10 2 cm) x (1 x 10 8 cm) f.(1 x 10 3 cm) x (5 x cm) g.(6 x 10 2 g) ÷ (2 x 10 1 cm 3 ) h.(4 x g) ÷ (2 x cm 3 )

Dimensional Analysis A method of problem-solving that focuses on the units used to describe matter that uses conversion factors. There are always two ways to show a conversion factor! 1m = 100 cm or 100 cm = 1 m 1 km = 1000 m or 1000 m = 1 km 1 hr = 60 min or 60 min = 1 hr

How many minutes are in 2.5 hours? Conversion factor 2.5 hr 60 min = 150 min 1 hr 1 hr cancel By using dimensional analysis, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

Examples 19. Make the following conversions using the prefix chart on #14. a. Convert 360 s to ms b. Convert 4800 g to kg c. Convert 5600 dm to m d. Convert 72 g to mg

Wait a minute! What is wrong with the following setup? 1.4 day 1 day 60 min 60 sec 24 hr 1 hr 1 min 24 hr 1 hr 1 min

Three targets with three arrows each to shoot. Can you hit the bull's-eye? Both accurate and precise Precise but not accurate Neither accurate nor precise How do they compare? Accuracy is how close your measurements are to the accepted value. Precision is how close your measurements are to each other.

Percent Error Percent error shows how accurate your measurement is:Percent error shows how accurate your measurement is: % Error = Accepted Value – Experimental Value x100 Accepted Value Accepted Value

Significant Figures The numbers reported in a measurement are limited by the measuring tool The numbers reported in a measurement are limited by the measuring tool Significant figures in a measurement include the measured digits plus one estimated digit Significant figures in a measurement include the measured digits plus one estimated digit

Rules for Significant Digits RULE 1. All non-zero digits in a measured number are significant.RULE 1. All non-zero digits in a measured number are significant. RULE 2. Zeros between non-zero numbers are significant.RULE 2. Zeros between non-zero numbers are significant. RULE 3. Other zeros are only significant if they follow both a decimal point and a non-zero digit.RULE 3. Other zeros are only significant if they follow both a decimal point and a non-zero digit.

Examples 27. How many significant digits are in each of the following measurements? a L e mL b. 820,400.0Lf x g c. 707,000kgg mL d sh x 10 5 kg

Significant Numbers in Calculations A calculated answer cannot be more precise than the measuring tool. A calculated answer cannot be more precise than the measuring tool. A calculated answer must match the least precise measurement. A calculated answer must match the least precise measurement. Significant figures are needed for final answers from Significant figures are needed for final answers from 1) adding or subtracting 1) adding or subtracting 2) multiplying or dividing

Adding and Subtracting The answer has the same number of decimal places as the measurement with the fewest decimal places one decimal place two decimal places answer 26.5 one decimal place

Multiplying and Dividing Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures. a X 4.2 = → 9.2 b ÷ 0.07 = → 60 c X = → X 0.060

Examples 30. Solve and round to the appropriate number of significant digits. a. 43.2cm cm + 48cm = __________________ b mg mg mg = ____________________ c cm – 3.14cm =___________________ d. 24m x 3.26m =________________________ e. 53.0m x 1.53m =___________________________ f m ÷ 51.2s =________________________ g. 168m ÷ 58s =_______________________