Enjoy your vacation!

Due to technical issues, I will be posting on Tuesday, 9/2/14. Enjoy your vacation!
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The first unit of your Chemistry course lays the foundation for measurement and the language of chemistry for the entire year. In my previous entry, I talked about measurement and significant figures. For this entry, I'm going to talk about a few more basic concepts that get the students prepared for the study of high school Chemistry. Objectives: 1. Identify four base units of measurement; identify and use prefixes kilo- through milli- . 2. Record measurements and perform calculations using scientific notation. Scientific study is conducted using or System Internationalunits -- also known as SI the metric system. Students have used this system over the years so it's not unfamiliar, but they have been on summer vacation and not really using it. Americans never really got rid of the English system of measurement (pounds, ounces, inches and Fahrenheit degrees), so a reminder is useful to students.From http://www.thefreedictionary.com/SI+system: Noun1. SI system - a complete metric system of units of measurement for scientists; fundamental quantities are length (meter) and mass (kilogram) and time (second) and electric current (ampere) and temperature (kelvin) and amount of matter (mole) and luminous intensity (candela); "Today the United States is the only country in the world not totally committed to the Systeme International d'Unites"International System, International System of Units, SI unit, Systeme International, Systeme International d'Unites, SImetric system - a decimal system of weights and measures based on the meter and the kilogram and the second Units students would used the most in high school Chemistry are grams, milliliters and centimeters. Later in the school year, moles will be used, and seconds as well.Here is a page with commonly used metric system units, symbols and prefixes: http://lamar.colostate.edu/~hillger/common.html This video provides a useful pneumonic for remembering the metric prefixes and a guide for converting metric measurement units: I will talk about the of unit conversion in my next post. I'm a big fan of this method and even use it for these metric conversions, but knowing another method is always useful (you can check your answer if you know a different way to complete a calculation). factor-label methodBy the way, I do instruct students to put a zero in front of the decimal point! Another topic to review briefly is the use of . scientific notationStudents use scientific calculators on a regular basis. Graphing calculators are required for many high school math courses; however, programs can be saved in these calculators that would solve the problems for them. I know that the New York State Regents Examinations in Chemistry and Physics do not allow the use of graphing calculators for this reason. It is the teacher's choice on what type of calculator to allow in the classroom. Consult with the other teachers in your department, or the head of your science department, to determine the calculator guidelines being used.For a standard scientific calculator, it's worth it to instruct your students NOT to press the 10 X button, but to use the EE or EXP button. When pressed, " x 10" will show up on the calculator screen and the power of ten can be entered. I highly recommend that you have a 5 minute lesson with your students or they will use their calculators incorrectly and answers will be off by a power of 10!Here's a 10 minute video showing various examples relating to the conversion of numbers and calculations with scientific notation: Instead of putting commas in the number, the convention is to simply leave a space between groups of 3 numbers (just don't write in the commas). For example, instead of 637,000 it would be reported as 637 000 . Adding and subtracting in scientific notation requires that the numbers be put into the same power of 10 (the same exponent). Then the addition and subtraction is relatively easy. Chemistry students most likely will be multiplying and dividing numbers in scientific notation. Here is a brief 7 minute video discussing all of these skills: BTW, (-6) - (-4) = (-6) + (4) = -2 . Here are a few worksheets to practice this important skill. These two pages contains basic conversion problems with answers: http://misterguch.brinkster.net/PRA039.pdf http://cdn.kutasoftware.com/Worksheets/PreAlg/Scientific%20Notation.pdf Here's a page with multiplying/dividing practice -- with answers! http://www.lavc.edu/math/math125/Worksheets/MDscientific.pdf This two-page worksheet contains scientific notation practice as well as math problems in scientific notation: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=40&ved=0CFcQFjAJOB4&url=http%3A%2F%2Fcbsd.org%2Fsite%2Fhandlers%2Ffiledownload.ashx%3Fmoduleinstanceid%3D23849%26dataid%3D15143%26FileName%3DScientific%2520Notation%2520Worksheet.pdf&ei=5Pr5U9jeCJatyASZjoCgDw&usg=AFQjCNG_yk726nH8gkDCixIFc6ST1EAslQ&bvm=bv.73612305,d.aWw This web page contains a mixture of worksheet options: http://teacherweb.com/GA/MarionCountyMiddleHigh/Welch8thmath/Scientific-Notation-Worksheets.pdf Remember to purchase my lab book "Chemistry on a Budget" . It is available at amazon.com and lulu.com for only $20! The book contains 13 labs that require consumable materials you can purchase at local stores.http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budgetEach lab is presented with two possible report formats -- both labs use the same procedure but each has a different conclusion -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired, and each version is designed to be just two pages. This way the teacher can photocopy just one 2-sided page per student (saves paper). Many of you are heading back to school, setting up your classrooms, and preparing for your first days -- some of you may even be starting classes this week. For those teachers, have a great school year! BTW, I'd love to hear from you with your questions or suggestions for blog topics. Have a great week! Typically the first unit in a Chemistry course contains information about Measurement and Significant Figures. Students must learn these essential skills -- they're important for this course and further study in the sciences. Objectives: 1. Compare accuracy and precision of measurements. 2. Apply the rules of identifying the significant figures in a measurement. 3. Apply the rules for calculation with significant figures (adding/subtracting and multiplying/dividing). Here is a brief video about accuracy and precision which shows two examples to aid in comprehension: Another important skill for students is to read a measurement using an instrument to the limit of its accuracy. One way I introduce this is for the students to use centimeter rulers to measure the width of their textbook (or a piece of paper or whatever is handy). I collect various measurements (or have students write them on the board) -- for example, the students could report 20.5 cm, 20.8 cm, 21 cm and 20.4 cm. I would then report the "true" answer as 20.53589123853295 cm. The students will be confused, recognizing, and possibly stating, that it is a made up number, that it's not possible to get this answer with the ruler being used. From there I discuss that it's important to read a measurement instrument to the limit of its accuracy, which means between the lines of the instrument. The last digit of any measurement is the uncertain digit because it is an estimate. Practice in reading measurements are in the following worksheets -- some are for younger students worksheet, but there are many examples to use. http://www4.smsd.org/debbiekapaun/docs/Doc-167686.pdf http://www.math-aids.com/images/measurement-reading-thermometers.png http://cdn.r1n.co.uk/img/resources/2012/07/16/01/01-07-24-954640399-300.png If you're feeling creative, possibly mimic this worksheet with fewer examples: http://ch017.k12.sd.us/Sturgis%20classes/mathworksheets/ruler%20worksheet.jpg This worksheet contains the readings of a graduated cylinder: http://www.mathworksheets4kids.com/capacity/reading-cylinder-decimals-large.png Remember that because water can adhere to the sides of the graduated cylinder forming a U-shape called a meniscus, the measurement is read in the center, or bottom, of the meniscus. Because looking above the cylinder can result in an inaccurate measurement, it is important to read the measurement at eye-level. For future calculation work, it is an important skill to recognize the significant figures or sig figs in a measurement.This page contains rules for assessing the sig figs in a measurement: http://www.usca.edu/chemistry/genchem/sigfig.htm These rules can simplified into two rules: 1. To count the significant figures in a number with a decimal point -- the first non-zero number and all numbers to the right are considered to be significant. I draw an arrow at that number and a line under all the numbers to the right.For example, 1010.0 cm has 5 significant figures. 2. To count the significant figures in a number without a decimal point -- the numbers from the first non-zero number to the last non-zero number are significant. I draw a bracket from the first non-zero number to the last non-zero number.For example, 1010 cm has 3 significant figures. Here are a few worksheets to practice this important skill: http://woodridge.k12.oh.us/ourpages/users/dweaver/Chemistry/PracticeWorksheets/MiscellaneousWorksheets/SigFigWorksheet.pdf https://www.everettcc.edu/files/students/rainier-learning-center/tutoring-center/chemistry/w316-significant-figures-worksheet.pdf http://www.math-only-math.com/worksheet-on-significant-figures.html Recognizing the sig figs in measurements is important for calculations and knowing how to round off the result. The rules are mainly for adding/subtracting and multiplying dividing are:1. When adding or subtracting measured quantities, round the result so it has the same number of decimal places as the least accurate measurement. 5.34 cm + 9.3 cm + 6.12 cm is simply listed and it can be difficult to see the least significant measurement. 5.34 cm 9.3 cm + 6.12 cm ---------------- With this layered organization, it is easier to see where the rounding will occur. 2. When multiplying or dividing measured quantities, count the number of sig figs in each measurement and round the resulting calculated value to the least number of sig figs in the measurements. For example, 0.0322 cm x 6.5 cm = 0.2093 cm2 (unrounded) -- counting the sig figs in the measurements, there are 3 and 2. The result is rounded to two significant figures, 0.21 cm2 -- because the 3rd significant figure is greater than 4. For constants or accepted values, all of the numbers are considered to be significant and the values are not considered to be limiting when rounding off calculations.The convention is to calculate first, then round off at the end. Because the rules for rounding are different for add/subtract and mult/divide, round at the end of one series of operations (adding/subtracting or multiplying/dividing) before switching to a series of operations with a different rounding rule. The following page contains three videos regarding these calculation rules: http://www.kentchemistry.com/links/Measurements/calcswithsigfigs.htm Notice that he cancels or combines the measurement units in the calculations. I will be talking about measurement units in a subsequent post. Also, his third video shows calculations with both add/subtract and multiply/divide calculations where rounding occurs in one calculation with one rule before switching to the other rule. This page addresses "Exact Values" as well. Thank you for your patience as I posted later due to illness. My next post will be Sunday, 8/24/14. Purchase my lab book "Chemistry on a Budget" -- it is available at amazon.com and lulu.com . The book contains 13 labs that require consumable materials you can purchase at local stores.http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budgetEach lab is presented with two possible report formats -- both labs use the same procedure but each has a different conclusion -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired, and each version is designed to be just two pages. This way the teacher can photocopy just one 2-sided page per student (saves paper). You may be enjoying the last few days of relaxation before going back to your school. Order my book and enjoy the rest of your summer -- it will get to you in a few weeks! I've been ill this week, so I will post a new entry on Tuesday, 8/19.
Thank you for your patience! Summer is ending and it's time to think about how to start off your class year. I recommend setting class rules at the beginning of the first day, but that won't take an entire class! One lab that is interesting, colorful, has temperature changes and gas production is "Flash in a Bag" (sometimes called "Chemical Reaction in a Bag". Students must wear goggles when performing this -- be prepared to talk about this lab's safety.Here's a simple demonstration of the reaction -- I made this a discovery experience, and could refer to it many times. I performed this lab with one bag (similar to the video) and actually twisted the bag between the solid and liquid reactants -- then the zip-loc bag could be sealed before the ingredients were mixed. I allowed the students to handle the bag during the reaction -- the temperature changes could be felt and the gas production was exciting! Again, goggles are to be worn, and students must to wash their hands, with soap, before removing their goggles.From this experience, you later can have a brief lecture about the signs of chemical change (color change, production of a gas, temperature change) as well as the concept of exothermic and endothermic change. If desired, the chemical reaction can be written, using it to introduce the chemical language, with phases noted, and even balancing to show a final result. Here is a lab page that is a brief set of lab instructions: http://www.chymist.com/Chem%20in%20ZipLock%20bag.pdf The indicator doesn't have to be measured, one or two pipets of indicator is sufficient. An explanation of the chemical changes observed was found at: http://www.elmhurst.edu/~chm/demos/reactioninbag2.htm A slightly edited version is below: Explanation: A chemical reaction occurs between the calcium chloride and the baking soda in which a double replacement reaction takes place. The two solids switch partners and form a new substance--the precipitate calcium carbonate. Calcium chloride + baking soda (sodium bicarbonate) --- calcium carbonate + sodium chloride + hydrogen ions CaCl2 + 2 NaHCO3 ---> CaCO3 + 2 NaCl + H+ ions As the reaction proceeds, the bicarbonate breaks down first to make hydrogen ions, an acid. This acid then converts some of the bicarbonate to carbon dioxide gas which begins to blow up the plastic bag. Hydrogen ions + sodium bicarbonate ---> carbon dioxide + water + sodium ions H+ ions + NaHCO3 ---> CO2 + H2O + Na+ A good summary of the reactions (on Page 3) is at: https://www.flinnsci.com/media/621024/91419.pdf This lab is an exciting beginning to the course for students and an simple preparation for the teacher. Check out my lab book "Chemistry on a Budget" available at amazon.com and lulu.com -- it contains 13 labs that require consumable materials you can purchase at local stores -- and it's only $20! http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budgetEach lab is presented with two possible report formats -- both labs use the same procedure but each has a different conclusion -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired, and each version is designed to be just two pages. This way the teacher can photocopy just one 2-sided page per student (saves paper). It will take a little time to get to you, so order it and enjoy the rest of your summer vacation! Have a good week! Students who receive a poor grade on a laboratory report sometimes ask to rewrite the lab to improve their grade. I eventually became proactive about this, and offered to meet with students, before the lab report was due, to provide feedback. Many students who took advantage of this strategy eventually received As on those reports.I required a one-on-one meeting with the student with the written lab in hand -- then I would read it in front of the student and provide the feedback as if I were grading it. When "advertising" this option to my students, I stated that the students who met with me, and made the improvements I suggested, usually received good grades on those lab reports. I did have a student try to give me a disk with the lab to be read on it, but I refused to review the lab -- I required my teacher meeting with the student and the printed out lab report as it was more affective. Another student met with me but made none of the corrections and simply erased the penciled in comments. This was a surprise but that was the student's choice. I talk about another strategy for making up missed lab activities (due to absence) in my lab book "Chemistry on a Budget" available at amazon.com and lulu.com -- it contains 13 labs that require consumable materials you can purchase at local stores -- and it's only $20! Each lab is presented with two possible report formats -- both labs use the same procedure but each has a different conclusion -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired, and each version is designed to be just two pages. This way the teacher can photocopy just one 2-sided page per student (saves paper). It will take a little time to get to you, so order it and enjoy your summer vacation! Have a good week! |
## AuthorMarjorie R. Heesemann is a chemistry teacher with 15 years of experience who is now working to develop resources for the Chemistry classroom. ## Archives
November 2017
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