Chemistry
What is Chemistry ~The science that deals with the materials of the universe and the changes these materials undergo. The study of the interactions of matter (atoms and molecules) and the energy involved
Gathering Information Observation- a fact you use one of your five senses to determine (the thermometer reads 24o C, this font is white) Inference- something you reason out (Heat entered the liquid causing the temperature to rise) Inferences are not as reliable as observations but sometimes required.
Problem Solving 1. Recognize some problem, and clearly state it. 2. Propose a possible solution to the problem, this is formulating a hypothesis. 3. Test your hypothesis by running some type of an experiment
Scientific Method ~A procedure for solving problems Observation Gather information Form a hypothesis Test your hypothesis Analyze your results Draw conclusion or restate hypothesis Repeat your work Publish or share it with others
It is not an exact sequence Repeat your work And share it with others Gather info Draw conclusion Form hypothesis Problem Analyze results Test hypothesis
Experiment There are many ways to experiment Variable- what you are testing only test one variable at a time A control group is necessary for an accurate comparison (the experiment without the variable) Blinded control groups don’t know they are the control Double blinded studies have patients who don’t know they are the control and experimenters who don’t know they are working with the control
Theories and Laws Common definitions of these words cause confusion. Theory- common definition is a hypothesis. An educated guess as to the solution of the problem. Law- a rule, that must be followed. THIS IS NOT THE DEFINITION OF SCIENTIFIC THEORY OR LAW!!
Theories and Laws Theory- attempts to explain why data gained from conclusions and observations are so. Law- summary of what is said in several conclusions and observations. Theories do NOT become laws! The names have nothing to do with level of acceptance.
Models Model- any representation of an object or a system A theory is sometimes called a model as it explains helps to explain how something works. The theory or model of how a gas works would be countless tiny particles (atoms and molecules) moving about rapidly colliding with everything. This is the best possible accepted account for why gas act the way they do.
Laws A Natural Law is a summary statement. Like Charles’ Law, put simply, heating a gas makes it expand, cooling it makes it contract. There is no why in a Law, just what happens. A law is NOT a more proven version of a theory, it is a different type of a statement.
Lab Safety
In the event of an accident… REMAIN CALM!!!!!! Get someone who knows what to do. Don’t do anything “helpful” unless you are asked someone is in serious danger
Appropriate Dress Goggles Closed shoes—No Flip flops or sandals. Long hair must be tied back. Nothing dangling loosely from you.
Lab Safety Equipment Fire extinguisher Fire Blanket Shower Eye Wash If there is a large fire on equipment or the room If a person is on fire If a chemical is spilled on someone’s body (everyone but the victim will leave the room) If a chemical is in someone’s eyes
Other equipment First Aid kit Broom and dustpan broken glass bucket Chemical Spill Clean up kit Gas turn off button Fire alarm for minor injuries for broken glass or metal all sharp objects go in here For chemical spills Turns off all gas to room in case of emergency pull
The Metric System and conversions
Why use the metric system? is it just to annoy American high school science students? It is used by (almost) the entire world except for the United States. (Myanmar and Liberia are the only other hold outs) Easy to replicate. Easier to convert between units.
The “SI” system SI is a subset of the metric system. SI stands for Systeme Internationale d’Unites or the International System of Units. length meter m mass kilogram Kg volume liter L temperature Kelvin/ Celsius K / C amount of substance mole mol
Metric Prefixes Name Symbol Meaning Tera T Giga- G Mega- M 1,000,000 1,000,000,000,000 Giga- G 1,000,000,000 Mega- M 1,000,000 Kilo- k 1,000 Hecto- h 100 Deka- da 10 (base) Deci d 1/10 Centi- c 1/100 Milli- m 1/1,000
Converting between Units (Dimensional Analysis, Factor Label Method) to convert one unit to another you need conversion factors. Conversion factor- how much of one unit equals another unit Ex. 1 kg = 2.2 lb or 1000 m = 1 km Therefore 1 kg/ 2.2 lb = 1 or 2.2 lb / 1 kg =1 you can always multiply any number by one and not change the number
Write down your given and underline it. draw an H or a field goal post next to it. in any H or field goal post you can put one conversion factor (half on top half on bottom). put the unit you want to cancel out on the opposite side of the field goal. multiply by everything on top, divide by everything on the bottom. Convert 52 lbs to kg. (2.2 lbs = 1 kg) 1 kg 52 lbs = 23.6 kg 2.2 lbs lbs divided by lbs cancel out
1 yd = .9144 m How many meters are in a football field (100 yds)? 100 yds 100 yds 1yd .9144 m =91.4 m .9144m 1 yd no, the units you want to cancel have to be on the opposite side. yards divided by yards cancel out You can always do more than one step with this method. How many meters is 100 ft? (1yd = 3ft) 100 ft 1 yd .9144 m = 30.5 m 3 ft 1 yds feet and yards cancel but you have to go to meters so…
1 kg = 2. 2 lb, 1000g = 1 kg 1000 mL = 1 L 30 mL = 1 fl oz, 3 1 kg = 2.2 lb, 1000g = 1 kg 1000 mL = 1 L 30 mL = 1 fl oz, 3.8 L = 1 gal How many kg are in 175 lbs? 175 lbs 1 kg 2.2 lbs = 79.5 kg how many grams are in 175 lbs? =79,500 g 175 lbs 1 kg 1000 g 2.2 lbs The key to doing multi-step problems is figuring out a “plan of attack” in the last problem I can convert lbs kgg, then fill in your H’s to match How many fl oz are in .32 gal? (you will need 3 H’s) 0.32 gal 3.8 L 1000 mL 1 fl oz 1 gal 1 L 30 mL =40.5 fl oz
If you have a unit expressed as a fraction.. put the number and the numerator as the given, and write the denominator below the line, then proceed with the rest of the rules convert 250 g/L to g/mL 250 g L 1 L =.25 g/mL 1000 mL liters cancel Convert 42 km/hr to m/s 1 min 42 km 1 hr 1 hr =11.7 m/s 60 min 60 s
Sig Figs Significant Figures
What are Sig Figs? I read on the Forbes list that Jimmy Haslam (owner of the Browns) has a net worth 1.8 billion dollars. Myself and a friend bought 4 tickets for $264.30 Assume that immediately after it was reported, I ran to Mr. Haslam with cash. Jimmy gets every penny and hasn’t had another expense yet. Does that mean Jimmy Haslam now has exactly $1,800,000,264.30? Of course not, all of those 0’s were actually numbers that we didn’t report because we didn’t measure accurately enough. The number was rounded!
This is where sig figs come into play Absolutely accurate measurements are impossible!!! We must round somewhere When we do calculations with these numbers we must reflect how accurate our initial numbers were. Significant digits means that digit was accurately measured Insignificant digit means that digit was NOT accurately measured.
Rules for determining if a digit is significant If it is not a zero, it is significant.123 If a zero is between two significant digits, it is significant. 309 Zeros at the end of a number with a decimal point are significant. 56.0 Zeros at the end of a number that do not have a decimal point are NOT significant. 82400 Zeros at the front of a decimal are NOT significant. .00562
Determine how many sig figs are in each number 734 100,025 6501000 .00034 2.00034 527.00 16.01 18700000000000
Round each number to the given number of sig figs (2) 734 (4) 101.025 (3) 651500 (5) .00334 (4) 132.084 (3) 527.00 (5) 16.01 (3) 18700
When adding or subtracting. How to report answers When multiplying or dividing. You can only have as many sig figs in your answer as you do in the number with the least amount of sig figs. 3.56 x 2.1= 7.476 7.5 (2 sig figs) When adding or subtracting. Numbers added to or subtracted from insignificant numbers are insignificant (rounded off). 347.58 + 21 368.58 369 insignificant
Examples 1.24 x 34 983200/ 124 772000 + 5710 323400 - 54000
Exemptions from sig figs some numbers have an infinite number of sig figs. Meaning we can ignore them in our calculations If a something = 1(unit), that one has an infinite number of sig figs. 1 yd = .9144 m many conversion factors have an infinite number of sig figs, for example 3 ft = 1 yd, 60 sec= 1 min, 100 cm = 1m. Not all conversion factors have an infinite number of sig figs though. .9144 m = 1 yd, 2.2 lbs = 1 kg. If you are ever unsure, ask me!
Important Rule Only use sig figs in your answer. Do NOT round in the middle of the problem!!!
Problem 1 yd = .9144 m 3 ft = 1 yd, 60 sec= 1 min, 100 cm = 1m. Convert 79 ft to yards to the correct number of significant figures.
Another A 17.5 g object is placed in a graduated cylinder. The volume of the water in the graduated cylinder rises from 12.5 mL to 23.5 mL. What is the density of the object to the correct number of significant figures?
Scientific Notation some numbers so large or small that is a pain to write out normally for example Jimmy Haslam has $1,800,000,000 To write in scientific notation write down all sig figs x10x The number is always written to the ones place with a decimal so the above number is $1.8x109
Quick conversions 6.7 x10-7 2.31 x105 5.79 x103 4.19 x10-5 .0065 94,100,000 .000000065 9,840
Scientific notation has to be used to correctly write some answers For example 1329 / 13 = 102.23 rounded to 2 sig figs would be… You Have To Write This Number In Scientific Notation! 1.0x102
scientific notation and your calculator To put numbers in scientific notation in your calculator there is normally an E or EE or EXP key That E EE or EXP replaces the x10 Pay attention to the way your calculator denotes scientific notation!!!
Temperature Conversions The United States is the only country to measure temperature in Fahrenheit. Most countries measure temperature in degrees Celsius. A conversion needs to be made Tc = (TF-32)(.56) TF = Tc(1.8) + 32 Kelvin is the SI unit of measure for temperature but is only used in extreme heat or cold situations K = Tc + 273 Tc = K - 273