CHEM 1110 Chapter 1
Chapter 1 OVERVIEW What s science? What s chemistry? Science and numbers Measurements Unit conversion States of matter Density & specific gravity Describing energy Heat and its transfer First things first
What is Science? The whole of science is nothing more than a refinement of everyday thinking. -Albert Einstein
What s chemistry? The Central Science Physics Chemistry Biology
What is Chemistry? The study of the matter, its composition, properties, and the changes it undergoes.
Scientific Method A way of solving problems or answering questions. Starts with observation- noting an recording facts Hypothesis- a possible explanation as to the cause of the observation, based on research and previous knowledge
Scientific Method Experiment- designed to test the hypothesis only two possible answers hypothesis is right hypothesis is wrong Generates data -observations from experiments. Modify hypothesis - repeat the cycle
Observations Hypothesis Experiment Cycle repeats many times. By you and by others The hypothesis gets more and more certain. Becomes a theory A thoroughly tested model that explains why things behave a certain way.
Observations Hypothesis Experiment Another outcome is that certain behavior is repeated many times Scientific Law is developed Description of how things behave Usually an equation Law - how Theory- why
Science and numbers Why does science have to use # s?
Types of observations Qualitative- descriptive, but not true measurements Hot Large Quantitative- describe with numbers and units 100 C 15 meters Scientists Prefer Quantitative data; More precise, testable, no bias
How good are the measurements? Scientists use two words to describe how good the measurements are Accuracy- how close the measurement is to the actual value. Precision- how well can the measurement be repeated.
Differences Accuracy can be true of an individual measurement or the average of several. Precision requires several measurements before anything can be said about it.
Let s use a golf analogy
Accurate? No Precise? Yes
Accurate? Yes Precise? Yes
Precise? No Accurate? Maybe?
Accurate? Yes Precise? We cant say!
In terms of measurement Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across. Were they precise? Were they accurate?
Why? Chemistry often deals with very large and very small numbers. There are 602,000,000,000,000,000,000,000 molecules of water in 18 ml one electron has a mass of 0.000000000000000000000000000911 g We need a shorter way of writing these numbers
Standard Exponential Form another name for scientific notation. consists of two parts a number between 1 and 10 multiplied by 10, raised to some power 602,000,000,000,000,000,000,000 = 6.02 x 10 23 0.000000000000000000000000000911 g = 9.11 x 10-28
Putting a number into scientific notation determine how many times you have to move the decimal place to make it into a number between 1 and 10 3240000 use that as the power of 10 3.24 x 10 6 Put this number into scientific notation 286543
What if the number is smaller? if you make the number bigger by moving the decimal point, make the exponent smaller and visa-versa 0.00045 4.50 x 10-4 Put this number into scientific notation 0.000006422
Getting back to original number Move the decimal point the same number of times as the exponent If the exponent gets bigger the number gets smaller Change 2.99 x 10 8 Change 4.87 x 10-3
Using your calculator EE and EXP button stand for x 10 to the 4.5 x 10-4 push 4.5 push either EXP or EE push 4 +/- or -4 see what your display says.
Practice these problems (4.8 x 10 5 ) x (6.7 x 10-6 ) (6.8 x 10-6 ) (3.2 x 10 4 ) Remember when you multiply you add exponents 10 6 x 10-4 When you divide you subtract exponents.
Adding and Subtracting You can t add or subtract numbers until they are to the same power of ten. Your calculator does this automatically. (4.8 x 10 5 ) + (6.7 x 10 6 ) (6.8 x 10-6 ) - (3.2 x 10-5 ) Remember- standard form starts with a number between 1 and 10 to start.
Really large, Scientific Notation and really small numbers
PEMDAS 2.4 10 3 4.8 10 3 4 1.2 10 3 4.8 10 4 3 1.2 10 2.4 10
Significant figures (sig figs) How many numbers mean anything. When we measure something, we can (and do) always estimate between the smallest marks. Measure in cm. 1 2 3 4 5
Significant figures (sig figs) The better marks the better we can estimate. Measure in cm. Scientist always understand that the last number measured is actually an estimate. 1 2 3 4 5
Significant figures (sig figs) The measurements we write down tell us about the ruler we measure with The last digit is between the lines What is the smallest mark on the ruler that measures 142.13 cm? 141 142
Rules for Determining Significant Digits All non zero numbers are significant 1,2,3,4,5,6,7,8,9 All zeros sandwiched in between non zero numbers are significant 101, 10001 Placeholder zeros are not significant Use the Atlantic-Pacific Rule
Pacific Atlantic Present Absent If the decimal point is absent, start at the Atlantic (right), find the first non zero, and count all the rest of the digits 230000 1750
Pacific Atlantic Present Absent If the decimal point is PRESENT, start at the Pacific (left), find the first non zero, and count all the rest of the digits 0.045 1.2300
Sig figs. How many sig figs in the following measurements? 458 g 4085 g 4850 g 0.004085 g 40.004085 g 405.0 g 4050 g 0.450 g 4050.05 g 0.0500060 g
Rounding rules Look at the number behind the one you re rounding. If it is 0 to 4 don t change it. If it is 5 to 9 make it one bigger. Round 45.462 to four sig figs. to three sig figs. to two sig figs. to one sig figs. 45.5 45 50 45.46
Numbers without sig figs Counted numbers 12 eggs in a dozen 32 students in a class Definitions 1 m = 100 cm 16 ounces is 1 pound No estimated numbers
Watch the Sig Figs When rounding, you don t change the size of the number. You should end up with a number about the same size. Use place holders- they re not significant. Round 15253 to 3 sig figs Round 0.028965 to 3 sig figs 15300 0.0290
Adding and subtracting with sig figs The last sig fig in a measurement is an estimate. Your answer when you add or subtract can not be better than your worst estimate. have to round it to the least place of the measurement in the problem.
For example + 27.93 + 6.4 First line up the decimal places 27.93 Then do the adding.. 6.4 Find the estimated numbers in the problem. 34.33 This answer must be rounded to the tenths place.
RULE: When adding or subtracting your answer can only show as many decimal places as the measurement having the fewest number of decimal places. Example: When we add 3.76 g + 14.83 g + 2.1 g = 20.69 g We look to the original problem to see the number of decimal places shown in each of the original measurements. 2.1 shows the least number of decimal places. We must round our answer, 20.69, to one decimal place (the tenth place). Our final answer is 20.7 g
Practice 4.8 + 6.8765 520 + 94.98 0.0045 + 2.113 500-126
RULE: When multiplying or dividing, your answer may only show as many significant digits as the multiplied or divided measurement showing the least number of significant digits. Example: When multiplying 22.37 cm x 3.10 cm x 85.75 cm = 5946.50525 cm 3 Check the number of significant digits in each of the original measurements: 22.37 4 significant digits. 3.10 3 significant digits. 85.75 4 significant digits. Our answer can only show 3 significant digits. 5946.50525 shows 9 significant digits, we must round to show only 3 significant digits. Our final answer becomes 5950 cm 3.
Multiplication and Division 3.6 x 653 2350.8 3.6 has 2 s.f. 653 has 3 s.f. answer can only have 2 s.f. 2400
Multiplication and Division Same rules for division. practice 4.5 / 6.245 9.8764 x.043