Unit one – fundamentals of chemistry notes Scientific method

1. Unit one – fundamentals of chemistry notes Scientific method Scientific method: The _____________________ approach to the ______________________ of scientific problems and the ______________________ of interactions in nature. Step 1:_____________________________________________________________________________ To begin the scientific process, a ____________________ must be clearly and specifically identified. Example of a defining a problem:________________________________________________ _____________________________________________________________________________________ logical observation solution Identifying a problem problem I can’t stay awake in chemistry class Man-made synthetic materials such as Styrofoam do not degrade

2. Gathering information Step 2:_____________________________________________________________________________ Before setting out to find the answer to a scientific question, ____________________________ must be gathered in the form of preliminary ____________________________. Sources such as ______________________ and ____________________ papers could be checked for existing information on the problem at hand. information Research journals scientific

3. Step 3: ____________________________________________________________________________ Once a problem or question has been recognized, a ____________________ or ________________________________ is constructed. In an experiment, hypotheses are not “correct” or “Incorrect”, they are _____________________ or ___________________________ by the data collected. If a hypothesis has been tested repeatedly and not contradicted, it is known as a _____________ or ___________________. A well- tested and verified hypothesis that describes a large body of information is known as a _________________________. Example of a hypothesis:_________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Formulating a hypothesis hypothesis Educated explanation supported Not supported theory postulate law I fall asleep in chemistry class because I don’t get enough sleep at night. by altering the chemical structure of Styrofoam, a degradable formula Can be established.

4. Step 4:_____________________________________________________________________________ A crucial step in the scientific process!!! ____________________ collected during this step needs to be ____________________ and ______________________________. Data can be collected in the form of _______________________________ or _____________________________________. There are two types of observations:_____________________________________ and_____________________________. __________________________ observations are made using the five senses while _________________________ observations are made using_______________________________. Think about qualitative as “what” and quantitative as ”how much”. Experimentation and observation data organized analyzed observations experimentation qualitative quantitative Qualitative quantitative instruments

5. Experimentation involves designing scientific tests that use _____________________. A ___________________ is defined as any factor that can affect the outcome of an experiment. The ________________________ variable is set and ____________________ by the experimenter (such as time). The ___________________ variable is the variable that ___________________________ when the independent variable changes (such as plant growth). Properly set-up experiments provide ________________________ groups as well as ________________________ groups. Control groups are set-up under “normal” conditions and are used to compare the experimental results to. variables variable independent controlled dependent changes control experimental

6. Drawing conclusions Step 5: ____________________________________________________________________________ Conclusions should be based on ______________________________ and analyzed ________________________________. Reference should be made to the original ________________________. Questions to think about in the conclusion may include: Was the hypothesis supported or not supported by the data? What were possible sources of error in the lab? What are some ways to improve the experiment? What are some questions yet to be addressed? observations data hypothesis

7. Important considerations: 1)    If the data does not support the initial hypothesis, the experiment was not pointless! 2)    If the original hypothesis or problem addressed needs to be modified, the whole process needs to start over. Sometimes an experiment that “goes wrong” opens the doorway to a new discovery.scientific method

8. Notes continued Significant figures Significant figures: all of the _________________ that are known in digits a ______________________ plus a last digit that is _____________________. Measurements should always be recorded to the correct number of significant figures! Example: Recording room temperature.  _______________________________________________________________ THINK ABOUT IT!!! Suppose you were given temperature data for various points in Frederick from a variety of sources and the data looked like this: 23.232C, 25.2C, 26.1746C, 27.12C If you wanted to find an average, how much should you round your answer???) measurement estimated 24.3 c 3 significant figures!

9. General Rule: An ________________ cannot be more _________________ than the _______________ precise _________________ from which it was calculated. When adding or subtracting, round to the same number of __________________ as the measurement with the ________________ number of decimal places. 3.451 7.982 3.45 1.41 1.02 - 1.1 +2.072 +2.1 answer precise least measurement decimal places least 2.35 11.102 2.4 6.933 6.93 11.1

10. multiplying dividing When __________________ or _________________, round the answer to the same number of ____________________ ______________ as the measurement with the ____________ number of significant figures. Examples: 2.1 x 1.301 =__________________ 4.02 x 2.945 = _______________ 0.034 x 3.223 = _______________ Significant figures least = 2.7 2.7321 11.8389 = 11.8 0.109582 = 0.11

11. Rules to identifying the number of sig. figs.: 1)Every ___________________ digit in a reported measurement is significant. 56.6, 2.34 and 978 all have _____________ significant figures (sig. figs). 2)_________________ appearing between ________________ digits are significant. 6007, 50.89 and 5.708 all have ________ sig. figs. 3)__________________ zeros appearing in front of _____________ digits are ____________________ and not considered significant. 0.000091, 0.042 and 0.42 all have ___________ sig. figs. Non-zero 3 nonzero zeros 4 leftmost nonzero placeholders 2

12. 4)Zeros at the _____________ and to the _________________ of a decimal point are _______________ significant. 57.00, 2.030 and 7.000 all have __________ sig. figs. 5)Zeros at the _____________ and to the _________________ of a decimal point are _______________ significant unless a careful measurement was actually made. 400, 4000 and 30000 all have ____________ significant figure. When calculating the correct number of significant figures in an answer, perform all of the calculations FIRST then round the final answer. end right always 4 left Right end not 1

13. Notes continued Scientific Notation Review A number written in scientific notation has two components: A _________________ and 10 raised to a _______________. The Coefficient must be greater than or equal to _________ and less than ______________. (2.3 x 103, 7.9 x10 -5) What is 540,000 in Scientific notation? _____________________ 5.4 x 10 = 54 For each positive power of ten, 54 x 10 = 540 the decimal point moves one 540 x 10 = 5,400 place to the right 5,400 x 10 = 54,000 4.67 x 103 =_________________ 54,000 x 10 = 540,000 2.71 x 104 = _________________ 5.4 x 105 = 540,000 For each negative power of ten, 4.5 x 10 –6 = ________________ the decimal point moves one 1.21 x 10 –3 = _______________ place to the left. coefficient power 1 10 5.4 x 105 4,670 27,100 0.0000045 0.00121

14. (Remember: 10 –1 = 1/10; 3.2 x 10 –1 = (3.2/10) = 0.32) Adding and Subtracting: THE _______________ MUST BE THE SAME! Add the coefficients, the exponent remains the same. 3.2 X 103 8.6 X 102Must be changed to ___________ +4.5 X 103 +1.1 X 103 Multiplying and dividing: Multiply/divide the exponents and follow these rules: exponents 0.86 x 103 7.7 x 103 1.96 x 103 Multiply: Multiply the coefficients, _______ the exponents add (4.0 x 102)(3.0 x 103)=_____________ Divide: Divide the coefficients, ____________ the exponents (4.0 x 104)/(2.0 x 102)=___________ 12 x 105 = 1.2 x 106 subtract 2.0 x 102

15. Notes on Accuracy and Precision _________________ is exact (there are 26 students in this class). _____________________ are subject to error. If each of the individual measurements in a set of data are close to the ______________ of the set, then they are ______________ . The _____________ of an individual measurement is determined by the piece of equipment used to take the measurement. Precision counting measurements average precise precision

16. For example: It does not make sense to measure room temperature on a thermometer marked in degrees Celsius and read that it is 25.53 degrees Celsius. The number of ________________ ________________ in a measurement is determined by all of the _______________ digits in the measurement plus one digit that is ___________________. In the temperature example, the 25 degrees is known and the 0.5 is estimated. The thermometer is not precise enough to read to the 1/100 of a degree. Significant figures known estimated

17. The ________________ of a set of measurements refers to the closeness of the average of the set to the “________________” value and depends on how _________________ the measurement was made. FOR EXAMPLE: A block of wood has a Length of 4.3 cm. A student measures the length of the block and finds it to be 4.4 cm. Another student measures the block of wood and determines its length to be 5.2 cm. Which measurement is more accurate?______________________________ accuracy accepted carefully 4.4 cm

18. Determine if each of the targets below represent low or high precision and low or high accuracy. ___________ Accuracy ______________ Accuracy ___________ Precision ______________ Precision ___________ Accuracy ______________ Accuracy ___________ Precision ______________ Precision poor good good good good poor poor poor

19. Which number is more precise? (think about the limitations of the balance used to make the measurement!) A)3.00 g B)3.000g C)3 g Which number is a more accurate measure of a 7.00 kg block? A)6.93 kg B)6.9 kg C)8 kg Remember to think about accuracy, precision and significant digits. An answer of 9.067894038399 L is not an acceptable answer on a lab, test or any other piece of paper that bears the privilege of sporting your signature. B! A!

20. Notes – percent error Accuracy of data can be analyzed using a percent error calculation. Percent error gives a mathematical value that represents the difference between the ________________________ value and the ______________________ value. The accepted value is the correct value (what the data should be – based on reliable _______________). The experimental value is the value measured in ________________. Formula for percent error: accepted value – experimental value ____________________________________________ x 100   accepted value What does it mean if the percent error is negative??? What value would have to be greater? accepted experimental research lab You got more than you expected! Experimental value

21. Notes - Uncertainty Precision can be given a mathematical value by calculating the ______________________ of a measurement. The uncertainty of a measurement is calculated as ___________________ of the value of the last certain ___________________ of the measurement. For Example: 7.24 g Last certain digit:____________________ Uncertainty = 0.5 x __________________ = _____________________ Uncertainty of the measurement: 7.24 g +/- Uncertainty of an instrument = half the smallest increment on the scale (1 increment = uncertainty of +/- 0.5) REMEMBER! The lower the uncertainty, the higher the precision of the instrument!!! uncertainty half digit 0.2 0.2 0.1 0.1

22. Base unit Abbreviation Quantity measured length time temperature mass Ampere A electric current candela cd luminous intensity mole mol amount of substance Notes - Metric measurements The SI (International system of units) is a system used around the world that is based on units of ten. metric systemsmart people  There are seven base units: m meter s second kelvin k g gram All other units are derived from the seven base units (and are thus known as derived units).

23. For example: Volume: Can be determined by three methods: 1)Using a formula: volume = ___________ x _________ x ____________ (UNITS=____________) 2)Measuring with a graduated cylinder: (UNITS=___________) 3)Determined by water displacement: (UNITS=________________) Remember that: 1 mL = 1 cm3 =1000 mm3 If a metal block displaces 8.0 mL of water, then its volume in cm3 is 8.0 cm3 and 8,000 mm3 because 8.0 mL x 1000 mm3/1 mL = 8,000 mm3. What is the volume in cm3of a metal toy that displaces 7.5 mL of water when dropped into a small container? width length height cm3 mL mL=cm3 7.5 cm3 Or 7,500 mm3

24. MASS Is the SI unit for mass a base unit or derived?___________________ What is the difference between mass and weight? When would your weight change, but not your mass? Mass:________________________________________________________________ _____________________________________________________________________ Weight: _____________________________________________________________ ______________________________________________________________________ Density:(Base unit or derived?) formula: density = Base unit The amount of matter in a given object The product of mass and gravitational force Derived! Units=g/mL Mass/volume

25. Temperature: There are three scales used to measure temperature: ________________________ ________________________ ________________________ ____________________ is the SI unit for temperature When dealing with calculations, it is often necessary to use prefixes. The distance from Maryland to Utah would be measured in _____. The length of a pencil would be measured in__________. The height of the letter h would be measured in____________. celsius fahrenheit kelvin kelvin km cm mm

26. prefix symbol 1 of these = this many base units in scientific notation mega M one million 1 x 106 kilo k one thousand 1 x 103 hecto h one hundred 1 x 102 deka dk Ten 1 x 101 * baseunit One 1 x 100 deci d one tenth 1 x 10-1 centi c one hundredth 1 x 10-2 milli m one thousandth 1 x 10-3 micro u one millionth 1 x 10-6 nano n one billionth 1 x 10-9 pico p one trillionth 1 x 10-12 SI Prefixes

27. Notes - Conversions To convert between units, move the decimal point _____ _____  _____ 0.4 4  40 400 K H D U D C M 5  50 500  5000  _____ ______ ______ As an alternative or for more complex problems, use dimensional analysis ( a.k.a the factor-label method). Step 1) write down what is known (number and unit) Step 2) set up a conversion factor with the target end unit on top and one known unit on the bottom Step 3) divide the product of the numbers in the numerator by the product of the numbers in the denominator Step 4) make sure that the final answer has the same number of significant figures as the number given 0.0004 0.004 0.04 500000 50000 5,000,000

28. Example: How many seconds are there in 7 minutes? Step 1)Known = 7 minutes Step 2) 7 minutes x ___seconds = 1 minute Step 3) 7 minutes x ___ seconds = ________seconds 1 x 1 minute all together, it looks like this: 7 minutes x ___seconds = _______ seconds 1 minute 60 420 60 60 420

29. Problem #2) How many cm are there in 5.2 meters? Problem #3) How many hours are there in 3 weeks?