1. Chemistry – Aug 28, 2017
P3 Challenge – Do Now
Name 3 different ways of understanding or communicating about chemistry. (There were 6 that we talked about.)
Hand in Lab Map and Equipment list (if not done so yet)
Check for Missing work on board

2. Objectives and Agenda Objectives Agenda Significant Digits
To Understand the Scientific Method
To Use Significant Digits
Agenda
Chemistry Defined and the Nature of Science
Experimental Design
Data Analysis
Laws and Theories
Significant Digits
Scientific Notation
Significant Digits in Calculations

3. Today’s Assignment What’s Due? (Pending assignments to complete.)
Significant Figure Practice Worksheet
What’s Next? (How to prepare for the next day)
Read p

4. Chemistry Defined
Chemistry is the scientific study of matter, its properties, and its changes.
Scientific Study…. using the scientific method
Of Matter…. anything that has mass and takes up space
Mass and weight
Its Properties … what can we measure
Its Changes … how does matter change over time

5. Nature of Science Observation Communication
Quantitative observations (measurements)
Qualitative observations (descriptions)
Communication
Without sharing information, observations are useless to advance human knowledge
Replication
Over time, place and observer
Falsifiable, Testable
Serendipity and Chance discoveries – Penicillium, Teflon, X-rays
Dr. Alexander Fleming, the bacteriologist on duty at St. Mary’s Hospital, returned from a summer vacation in Scotland to find a messy lab bench and a good deal more.
Upon examining some colonies of Staphylococcus aureus, Dr. Fleming noted that a mold called Penicillium notatum had contaminated his Petri dishes. After carefully placing the dishes under his microscope, he was amazed to find that the mold prevented the normal growth of the staphylococci.
The story of Teflon™ began April 6, 1938, at the Chemours Jackson Laboratory in New Jersey. Chemours chemist, Dr. Roy J. Plunkett, was working with gases related to Freon™ refrigerants, another Chemours product. Upon checking a frozen, compressed sample of tetrafluoroethylene, he and his associates discovered that the sample had polymerized spontaneously into a white, waxy solid to form polytetrafluoroethylene (PTFE).

6. Experimental Design
Determine what factors or variables you are interested in studying.
Identify Independent and dependent variables. (IV and DV)
Your experiment may have more than one of each.
An IV is one that you can manage and set levels or cases.
A DV is one that you observe.

7. Experimental Design
A control is one cases where the IV is absent, yet all other features of the experiment remain the same, and the DV is observed.
Controls necessary to show measurable effects, to rule out other explanations, to allow for conclusions to be drawn.
A hypothesis is a guess about the relationship between your variables of interest.
Science is not a linear process. See also Figure 8 on pg 46.

8. Data Analysis
After you perform the experimental trials as outlined by your design, you will have a data set to analyze with several observations of the same event.
Average result
Compare to a known or expected result using a percent error.
% 𝒆𝒓𝒓𝒐𝒓= 𝑨𝒗𝒆𝒓𝒂𝒈𝒆 −𝑬𝒙𝒑𝒆𝒄𝒕𝒆𝒅 𝑬𝒙𝒑𝒆𝒄𝒕𝒆𝒅 ×𝟏𝟎𝟎
Range = Max observation – Min observation.
May use a graph to show relationships between variables.

9. Accuracy and Precision
Accuracy – low % error – how close is the Average to the Expected
Precision – small range – how close are the data to each other

10. Evaluating Results Two Sources of error
Systematic errors
Random errors
Systematic (should be minimized with careful attention to lab techniques)
Instrumental (Ex: Every piece of measuring glassware has an uncertainty associated with it. Marked on the glassware.)
Procedural (Ex: During a chemical processing, every transfer from one vessel to another creates some additional error)
Tends to influence resulting data to be skewed in one direction

11. Evaluating Results Random Error vs a mistake
Can never remove uncertainty because of the fundamentally random nature of the motion of atoms.
Influence of the observer (uncertainty principle)
Tends to increase uncertainty of a measurement in all directions.
Error vs a mistake

12. Laws and Theories
A scientific law is a statement or mathematical equation that reliably describes a behavior of the natural world.
Ex: Law of Conservation of Mass – Antoine Lavoisier
Summarizes macroscopic and atomic phenomena (What happens)
A scientific theory is a well-tested explanation of observations.
Ex: John Dalton’s Atomic Theory
Explains macroscopic and atomic phenomena (Why does it happen)
Conflicting Info for a theory  Revise or replace

13. How to measure
Uncertainty depends on the measurement device used and on how it is used to measure.
Identify the smallest gradation marked on the measurement device.
Measure to this level of precision (certain measurement)
Add one more digit as an estimation of the true measurement’s location between the smallest gradation marks. (source of uncertainty)
Try to decide on one of the five statements below. If you can’t decide between two statements, use the odd digit between.
0 right on the line, 2 just above the line, 4 almost halfway, 6 a little more than halfway, 8 nearly to the next line.

14. Practice

15. Exact and Inexact Numbers
Counting items gives an exact number (e.g. 12 apples = exactly 12 apples)
Definitions within a measurement system give exact numbers (e.g. exactly 12 inches = exactly 1 foot, by definition)
Measurements give inexact numbers (e.g. 5.7 m)
In science, we don’t use fractions.
Conversion factors between systems of measurements give inexact numbers. (e.g. 1 lb = approximately kg… to 4 sigfigs)
Agreed uncertainty is ±1 for the digit in the last decimal place reported or measured
5.7 m means 5.7 ± 0.1 m m means 940 ± 10 m
2.54 cm means 2.54 ± 0.01 cm

16. Determining Significant Figures
The digits of a measured number indicate the level of precision for the measurement.
All non-zero numbers are significant.
Leading zeros are never significant.
Confined zeros are always significant.
Trailing zeros are significant if and only if a decimal point is present.
Ambiguous numbers like 300 mL can be made clear by using a decimal point, a line over the last significant digit, or better, use scientific notation.

17. Practice identifying sigfigs
40.7 L m
250. cm km
85.00 g mm kg
2000 cm

18. Scientific Notation
A clear way to report numbers that are either very large or very small, or numbers with an ambiguous number of significant figures
Two parts: Mantissa x 10exponent
Mantissa, or decimal part, is a number with one non-zero digit to the left of the decimal point that contains all significant digits, and only significant digits
Exponent indicates the decimal place location for the digits.
Exponent = number of places the decimal point must move to be placed to the right of the first significant figure
Large numbers have positive exponents and small numbers have negative exponents.
2000 cm  2.00 x 103 cm makes the significance clear.
Use Sci Not if you need clarity or you need to use more than 3 zeros.

19. Multiplication/Division with Significant Figures
Perform the calculation indicated.
Round your answer to the same number of significant figures as the number with the least number of significant figures that was used in the calculation.
DO NOT report all digits shown in your calculator
Round down for 4 or below.
Round up for 5 and above.
If a data set has a lot of rounding from 5, you may want to use engineering rounding: Round to an even digit result.
Ex: 1.92 m x m = m2 How should this be rounded?

20. Addition/Subtraction with Significant Figures
Perform the calculation indicated.
Round your answer to the same number of decimal places as the number with the least precise decimal place that was used in the calculation.
DO NOT report all digits shown in your calculator
The number of significant figures may increase or decrease.
Hint: Remove any scientific notation, then add/subtract numbers vertically. The place with a significant digit for all numbers is the place to round your answer.
Ex: 0.92 m m = m How should this be rounded?

21. Exit Slip - Homework What’s Due? (Pending assignments to complete.)
Significant Figure Practice Worksheet
What’s Next? (How to prepare for the next day)
Read p