Chapter 3 & A Li’l Bit About “Moles”

Chapter 3 & A Li’l Bit About “Moles” Plus some problem-solving techniques from Chapter 4. We aren’t going to do all of chapter 4, but if YOU are having difficulty with problems, I would review this chapter in detail on your own.

Objective A (remember, the objective refer to the Study Guides)http://www.magazine-agent.com/officials-logic-problems/magazine • Look at the following numbers. How easy would it be to memorize this list and regenerate it in a week or so on a quiz? • 1, 3, 5, 11, 21, 43, 85, 171, 341, 683, 1365, 2731, 5461, 10923, 21845 • Pretty hard? Pretty Easy? Why? • Easy huh? OK, what’s the next number in the sequence? How about the next 5 numbers?

How bout this?http://shop.crackerbarrel.com/online/shopping/default.asp • What if I never mentioned the list again? What if at the end of the semester…the day before the SOL…I asked you to remember those numbers? • Could you do that? • If so, you’re going to do really, really well when I asked you to memorize some “polyatomic ions” on page 147 of your textbook. • My guess is you wouldn’t remember though. Cracker Barrel “Brain Teaser” Game

Can you make sense out of NONSENSE? • Force Hour Upon Neigh • Koran Force Cis Shun • Heaven Fodder Count • Ye Brat Anent • Sago Farce Anew • No luck?

The Gettysburg Addresshttp://www.old-picture.com/defining-moments/pictures/Abraham-Lincoln-Antietam-Battlefield.jpghttp://en.wikipedia.org/wiki/Gettysburg_Address • “Four score and seven years ago our fathers brought forth on this continent a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.” • Abraham Lincoln delivered these words on Nov 19, 1863. (Go back a slide and read down instead of just left to right). • Being able to look at something new, and make sense of it is an important skill for the rest of this course. Yes, Ms Rackley, I know this was Antietam, but it’s a nice picture.

1, 3, 5, 11, 21, 43, 85, 171, 341, 683, 1365, 2731, 5461, 10923, 21845http://www.antiqueradiomuseum.org/RR%20Rule%20Book%20for%20CMSP&P%20RR.jpg • The numbers don’t seem to follow any kind of pattern. • But, what if you knew a rule? It wouldn’t just be memorization then. • OK, good point! The rule is: • Start with 1. • Double and add 1. • Double and subtract 1. • And so on. You just wish it was that EASY!

Let’s look at the numbers againhttp://equintconsulting.com/wp-content/uploads/2008/10/istock_000005164183small.jpg • 1, 3, 5, 11, 21, 43, 85, 171, 341, 683, 1365, 2731, 5461, 10923, 21845 • Start with 1. • Double and add 1. Doubling 1 gives me 2 and adding one gives me 3. • Double and subtract 1. Doubling 3 gives me 6 and subtracting 1 gives me 5.

Learn HOW to do the problem; don’t just memorize the answer!http://familyfun.go.com/Resources/printable-previews/previews/beaver_memorygame_august2.jpg Don’t • Doesn’t “knowing the rule” make the list easier to memorize? • You don’t have to memorize a bunch of unrelated numbers. • IF YOU KNOW the rule, you can generate the number list on the test easily. Anytime! Anywhere!

OK, does this relate to Chemistry at all? • What makes Chemistry hard for most students, is you DON’T know the rule. You didn’t read the book. You didn’t look at the sample problems. You don’t know the RULE! • Every problem looks like it’s a totally brand new problem. But you’re not solving for x or y. You’re finding the “density” or some other REAL PROPERTY of matter. • Every problem looks totally unrelated to anything we’ve done before.

Objective Ahttp://www.52shows.com/wp-content/uploads/2009/02/huh.jpeg • If we can understand the rules, it makes the problems much, much easier. And if you figure out how to do one problem, you should be able to figure out other problems just like it (like on the test). • Let’s start with a simple problem. I’ll give you two numbers, and you tell me the answer. • The numbers are 2 and 3. • What’s the answer?

Objective Ahttp://www.platformnation.com/wp-content/uploads/2009/06/shrugging.jpg • What are you supposed to do with those numbers? • It’s like that in Chemistry. If you don’t have a clue, anything you do is potentially just as valid as anything else. • But usually it’s pretty easy to figure out what to do. What?

Objective Ahttp://www.tvgasm.com/newsgasm/Bill-nye.jpg • In Chemistry, when we have numbers, much of the time we do one of three things: • Multiple 2 x 3 • Divide 2 / 3 • Divide 3 / 2 • If you can figure out which operation to do when, you can actually solve the problem. That’s our goal. What would Bill Nye do? Bill Nye is the Guy!

Objective Ahttp://francisanderson.files.wordpress.com/2009/01/billy-mays.jpg • We don’t use abstract or imaginary or hypothetical quantities in chemistry. • We use real amounts WITH UNITS. • 5 grams • 14.7 milliliters • 3.6 x 10-3moles (don’t worry about moles for a while…we’ll get to these) • 6.02 x 1023 molecules But wait! There’s more!

Objective Ahttp://www.vintagecalculators.com/html/texas_insturments_ti_58.html Note the cool red LED numbers • Notice on the last slide, most of the the numbers aren’t as nice as 2 or 3. • But so what. You have a calculator. Calculators don’t care how hairy the numbers are…they just add ‘em up. • You need to get in the habit of always using units. If the units in your answer don’t work out right, the problem is WRONG. Try again. Second calculator I ever got (1977). I got my first one in 1975 and all it did was add, subtract, multiply, divide AND do square roots. Quite an upgrade!

Units TELL you the right ANSWER! • If your units don’t work out right, your answer is wrong. • Do the problem over. Read the problem carefully before you start, and check your work when you get done. • Don’t just ignore wrong units. It is a big clue for you. This is very important. • LISTEN to the units!

Qualitative and Quantitative Data • Qualitative (think quality) • This is more a description. These are observations usually. • It’s blue. It’s hot. It’s cool. It’s smells like rotten eggs. • Remember to look for qualitative date when you do your lab experiments. • Quantitative (think quantity or amount) • This is telling me how MUCH of something you have. • 5.0 g of baking soda. 2L of diet Coke. 4.5 moles of CO2. • Remember to record quantitative data in your lab notebook when you do experiments too.

Objective B Math Alert! • Scientific notation is used to express very large and very small numbers. • Two very important numbers in chemistry are • 6.02 x 1023 = 602,000,000,000,000,000,000,000 (Avogadro’s Number) • 6.6 x 10-34 = 0.00000000000000000000000000000000066 (Planck’s Constant) • One is a VERY LARGE number. One is a very small number.

Objective Bhttp://phoenix.fanster.com/suns/files/2009/05/pile-of-money.png • 6.02 x 1023 is very large. • Let’s say you had that much money. • $602,000,000,000,000,000,000,000.00 • If you spent a billion dollars every second of every day, how long do you think the money would last?

Objective Bhttp://musikality.net/wp-content/uploads/2009/02/shocked.jpghttp://hebrewandgreekreader.files.wordpress.com/2009/05/waynes_world_15b15d.jpg • Answer: • More than 19 million years! Way! No Way!

Power Point Assignment • Another one for everyone…we are going to study “moles” in Chap 7. However, I want to introduce moles much earlier than that, and Chap 3 seems like a great time to do so. • Research moles online and write a 150 word summary about moles. (Note: mole is a chemical UNIT and not a little creature that burrows into the ground.) • Be prepared for a one question quiz on Chap 3!

Scientific Notation(we now resume our regularly scheduled power point…) • We use scientific notation to more easily represent very large and/or very small numbers. • We represent numbers as a “factor” times a power of 10. • Let’s look at 500, as an example.

Scientific Notation • 500 = 5 x 10 x 10, right? • But 10 x 10 = 100 and as you know, 100 = 1 x 102. • So we can rewrite 500 as 5 x (1 x 102). • But 5 x 1 just equals 5, so we usually ignore the “1” and just write 500 as 5 x 102. • That’s scientific notation. I’m sure this is just a review for all of you.

Scientific Notation • How about 999? The decimal point moves from left to right. • 999 = 9.99 x 10 x 10 • So, 999 = 9.99 x 102. • When you put a large number into scientific notation, the exponent will be positive.

Scientific Notation • How about 0.0014? • Well, 1.4 divided by 10 = 0.14. • 0.14 divided by 10 = 0.014. • 0.014 divided by 10 = 0.0014. • So we’re dividing by 10 and doing it 3 times.

Scientific Notation • So 0.0014 = 1.4 ÷ 10 ÷ 10÷ 10 • Or 0.0014 = 1.4 ÷ 103 since we are dividing by 10 three times. • 1.4 = 1.4 x 10-3 ------- 103

Scientific Notation • So 0.0014 = 1.4 x 10-3. • The decimal point moved from left to right. • When you put a small number into scientific notation, the exponent will be negative. • Remember that these are exponents. Negative exponents don’t mean negative numbers, they mean very small numbers (between 0 and 1).

Scientific Notation • 103 = 1,000 • 102 = 100 • 101 = 10 • 100 = 1 (NOT 0!!) • 10-1 = 0.1 • 10-2 = 0.01 • 10-3 = 0.001 Go up, multiply by 10 Go down, divide by 10

How do we add or subtract using scientific notation? • Make the exponents the same, if necessary, and then just add. • 5.4 x 103 + 2.6 x 102 = ? • Let’s change the second number so that the exponents match up… • 5.4 x 103 + 0.26 x 103 = 5.66 x 103

How do we add or subtract using scientific notation? • Does that make sense? • Well 5.4 x 103 = 5,400 • And 2.6 x 102 = 260 • So 5,400 + 260 = 5,660. Putting that back in scientific notations gives us 5.66 x 103. • Either way, your calculator will do it for you without any problems. Maybe!! Use parentheses with scientific notation on TI-83 and TI-84 graphing calculators or you will get the wrong answer. Math Alert!

How do we multiply or divide using scientific notation? • Even simpler • To multiply, you multiply the numbers and add the exponents. • 4 x 107 × 2 x 10-3 = 8 x 104 (80,000) • To divide, you divide the numbers and subtract the exponents. • 4 x 107 ÷ 2 x 10-3 = 2 x 1010 (20,000,000,000) × ÷

Sample Problems on Scientific Notation • A 91.43 • B 0.000000000154 • C 6,378,000 • D 0.000008 • E 149,600,000,000 • F 8934.8

Objective c…Accuracy, Precision and Errorhttp://www.edupics.com/en-coloring-pictures-pages-photo-dartboard-p9574.jpg • Think of a dartboard. You are trying to hit the bullseye. • Accuracy is hitting what you are aiming for. • Precision is hitting the same spot over and over. Is this accurate, precise, or both, or neither?

Objective c…Accuracy, Precision and Errorhttp://comps.fotosearch.com/comp/IGS/IGS170/dartboard-darts_~IS028-013.jpg • Think of a dartboard. You are trying to hit the bullseye. • If you hit the edge of the dartboard, you are not accurate. • If your darts are all over the place, you are not precise. Both accurate AND precise!

Objective c…Accuracy, Precision and Errorhttp://www.durhamtech.edu/graphics/programs/univtransf/chemlab1lg.jpg Take your time. Know what you are doing BEFORE you do it. Pay attention to detail. No one in this group is not involved. You’ll get good results. Everyone working together safely and observing what’s happening. • In Chemistry labs, we will take measurements. • Accuracy is how close you are to the TRUE value. • Precision is how close all of your measurements are to each other.

Objective c…Accuracy, Precision and Error • Can you be accurate (or have accuracy) with only 1 measurement? • Can you be precise (or have precision) with only 1 measurement? Yes, accuracy is compared to a “true” value. No, precision is “closeness” to all other measurements

Objective c…Accuracy, Precision and Error Accurate, Not Precise • Student A had 3 measurements: 80, 85, 90 Average = 85.0 • Student B had 3 measurements: 84.9, 85.0, 85.1 Average = 85.0 • Student C had 3 measurements: 82.1, 82.2, 82.3 Average = 82.2 • Student D had 3 measurements: 70.2, 82.2, 94.2 Average = 82.2 • The accepted value = 84.9. Who is accurate? Who is precise? Accurate, Precise Not Accurate, Precise Not Accurate, Not Precise

Objective C…Error • I put the formula for error and % error in your study guide. • The error is the difference between the experimental value and the actual or true value. We take the “absolute value” because there’s no such thing as “negative error.” • Being 5% high is the same as being 5% low. You still have 5% error in either case.

Objective C…Error • If the actual value is 10, it doesn’t matter if you get 9 or you get 11. You are still off by a unit of “1” • % error = Error / True Value x 100 • Using our example, % error = 1/10 x 100 or 10%.

Objective C…Error • We will discuss error primarily in our labs. Be sure to include a discussion of any errors that happened in your experiment in your “Analysis of Data” section of your lab report. • What kind of errors can you have in your labs? • Two kinds: • Random • Systemic

Objective C…Errorhttp://www.budapesthotels.com/sitepic/error_button.pnghttp://images.intomobile.com/wp-content/uploads/2009/06/easy-button.jpg • Random errors are mistakes. You can take care to reduce or eliminate random errors. These usually come from being unprepared (not reading the lab prior to doing it), rushing to get done, and careless errors (like forgetting to do a step). • Systemic errors are errors that are present in your system. You can’t do anything about these. If your data is precise, but not accurate this might indicate that you had systemic error. Easy Button Error Button

Objective d…Significant Figureshttp://www.musicdirect.com/shared/images/products/large/aayremyrtle.http://becauseican.co.za/wp-content/uploads/2008/04/ruler_0_10.jpghttp://mrsdlovesscience.com/meniscusirr.jpg • Measure the block of wood using the ruler. How long is it? • How much water is in the graduated cylinder? 23.0 mL ?? mL

Objective d…Significant Figures • When you take measurements in Chemistry class or in lab, you have to worry about how many significant figures (usually abbreviated as sig figs) you have. • What are sig figs? • All the digits you can read and the first one you can estimate. Between 7.1 and 7.2, so record as 7.15. All 3 digits are significant, because you read the first 2 and estimated the last 1.

Objective d…Significant Figureshttp://www.freefoto.com/images/2000/98/2000_98_1---Number-Zero_web.jpg Significant? Maybe or maybe not! • However, if you didn’t measure it, there are rules for figuring out how many sig figs something has. • RULE #1. All non-zero digits are significant. • So that means that the only thing you have to determine is whether or not the zeros are significant.

Objective d…Significant Figures • Rules are in the study guide. • 2. Zeros between non zero digits are significant. So, 2.003 has 4 sig figs. • 3. Zeros at the end of a number AND to the right of the decimal point are significant. So, 1.000 has 4 sig figs. • 4. Zeros at the beginning of a number are never significant. So, 0.00034 has 2 sig figs. • 5. Exact measurements or exact quantities have an unlimited amount of sig figs. Example 1 hour = 60 min. “1” and “60” both have an unlimited number of sig figs.

Objective d…Significant Figures • Adding/Subtracting • Answer cannot have more sig figs AFTER the decimal point than the number with the lowest number. • Ex: 2.1 + 2.22 + 2.345 = 6.665 • Answer can only have 1 digit after the decimal • Correct answer = 6.7 • Multiplying/Dividing • Answer cannot have more sig figs than the number with the lowest number of sig figs. • Ex: 2.22 x 2.345 = 5.2059 • 2.22 has 3 sig figs and 2.345 has 4 sig figs. Answer can only have 3 sig figs. • Correct answer = 5.21 ±1 sig figs off is usually OK. If answer should have 4 sig figs and you have 3, 4 or 5, I won’t mark it wrong.

Objective d…Significant Figureshttp://www.tvguide.com/celebrities/stuart-scott/214001 • But isn’t 50 and 50.0 and 50.00 and even 50.000 the exact same number? • Maybe, outside of chemistry class, but not in here. • Let me explain. 50 ≠ 50? Wha-hap-happen?

Objective d…Significant Figures • 50 means that your measurement is somewhere between 49 and 51. • 50.0 means that your measurement is somewhere between 49.9 and 50.1 • 50.00 means that your measurement is somewhere between 49.99 and 50.01 • 50.000 means that your measurement is somewhere between 49.999 and 50.001 The more sig figs in your measurement, the more confidence you have that it’s “exactly” 50 mL or g.

Objective e…SI Units AKA The Metric Systemhttp://www.boston.com/ae/celebrity/more_names/blog/KG.JPG • You need to know THESE: • Meters for length (m and cm and nm) • Kilograms for mass (kg and g) • Kelvin for temperature (K) • cm3 or liters for volume (L and mL) • Kilopascals for pressure (KPa and atm) 1.0 KG?

Objective e…SI Units AKA The Metric System • You need to know • Kilo means 1000 times (1 g = 1 kg) • Centi means 1/100th (100 cm = 1 m) • Milli means 1/1000th (1,000 mm = 1 m) • Micro means 1/1,000,000th (1000 μg = 1 mg or 1,000,000 μg = 1 g) • Nano means 1/1,000,000,000th (1 billion nm = 1 m) • Å = Angstrom means 1/10,000,000,000th (10 billion Å = 1 m) Certified SI Genius μ (mu) = micro

Objective f…Densityhttp://www.tungsten-spheres.com/density_model.jpg • Density = mass / volume • Usually has units of g / cm3 • Density of water = 1.000 g / cm3 • You should memorize this number! • Density is the mass in grams of 1 cubic centimeter of volume. Densely packed

Chapter 3 & A Li’l Bit About “Moles”