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Transcript of Chemistry
Observations & Inferences
What is Chemistry?
Chemistry is a branch of science which describes matter & the changes in matter.
Measurement - Quantitative Observations
How do we solve problems?
Scientific method - organized step-by-step thought process used to solve a problem
Unit 1: Introduction to the Scientific Method & Measurement
may involve seeing, feeling, hearing, or using a measuring device. Scientists carefully record observations as part of the scientific process. Analysis of observations allows the scientist to infer conclusions.
is a logical conclusion based on observation or deductive reasoning.
Inductive vs. Deductive Reasoning
Science is the study of the world around us. Science - searching for a cause & effect.
Pure Science: For discovery & explanation
Applied Science/Technology: put discoveries to use - to better mankind - leads to more technology
Define the problem (after observing a situation)
Research the problem
Past Hypotheses & Laws
Form a hypothesis - a proposed explanation based on observations & prior knowledge
If (I do this), then (this will happen)
Design & perform tests (experiment)
Qualitative Data: (without numbers) a description in words of what is seen, felt, touched, heard
Ex: Round, green, fuzzy, loud
Quantitative Data: (with numbers) measurements
Ex: 23.5 cm, 61.83 mL
Search for relationships
Make graphs, calculations
Interpretation of Relationships
Evaluate the hypothesis
Either reject the hypothesis or support the hypothesis
YOU CAN NEVER PROVE A HYPOTHESIS 100%
Perform additional tests
A scientific theory is an explanation that is strongly supported by scientific evidence. Scientific theories are usually validated by repeated observation and experimentation. In short, scientific theories describe why things happen.
A law of nature is a statement that describes a natural phenomenon that always happens the same way under the same set of circumstances. Laws are descriptive. They do not explain the science behind the phenomenon. For example, all gases can be measured to behave similarly at the same temperature and pressure. This is a statement of fact, and it is described by the ideal gas law. In this example, the ideal gas law does not describe why this phenomenon occurs. Instead, it only describes what occurs
The measurement can be repeatable by others. (All close to the same value)
Someone else could use the same equipment and get the same measurement
Test Tube Holder
Close to the accepted value
Data collected via qualitative (descriptions) or quantitative (numbers) methods are FACTS only.
Observations are made using one or more of your five senses.
An interpretation attempts to explain an observation.
Example: the light bulb glowed BECAUSE electricity was going through the filament, making it hot.
Not all numbers are significant!
1. All non-zeros ALWAYS count
2. Trapped zeros ALWAYS count
3. Trailing zeros ONLY IF a decimal is present or a line over it
4. Zeros before the first 1-9 number NEVER count
Calculating with Significant Digits
Answer should have the # of decimal places as the number with the least number of decimal places because you cannot be more precise than the least precise number.
Ex: 2.65435 + 1.1 = 3.7
4.795 - 2.3 = 2.4
Answer should have no more sig figs than the factor with the least number of significant figures - you can only be as precise as the least precise number.
Ex: 1.15 x 2.3 = 2.6
A unit made through a calculation of measurements
Ex: Measure the mass and volume and you can calculate the density.
SI (international) Units
Each unit of measurement has a base that can have a different prefix added.
Length = meter (m)
Mass = gram (g)
Volume = liter (L)
Temperature = Celsius (c)
or Kelvin (K)
Time = Second (s)
Commonly Used Prefixes
1000 x larger
Scientific notation is how scientists easily handle very large or very small numbers.
Density = mass/volume
Density describes how much matter is in a certain amount of space.
(also called Factor-Label Method or the Unit Factor Method) is a problem-solving method that uses the fact that any number or expression can be multiplied by one without changing its value. It is a useful technique.
When to use Dimensional Analysis
Use this method when you are trying to change the units for a measurement (ex: inches to centimeters)
EX: Mrs. Polson is 63 inches tall. How many meters is that?
Hint: You need to know how many centimeters is in an inch, and how many centimeters are in a meter.
1. Record a number for every line on the instrument.
2. When you run out of lines estimate the last digit
3. If it is right on the line estimate a zero
4. More lines = more accurate
When you use a graduated cylinder, read from the BOTTOM of the meniscus (curve)
Percent error describes how far away from the expected value your result is, or how much error you have in your experiment.
% error =
True Value - Observed Value
Percentage Error vs.
Say you got 52/61 on a test.... how do you calculate your percent?
% = 52/61 = 85%
What if you had to calculate the percent you got wrong?
% wrong = (#wrong)/61 = (61-52)/61
That's the same as percent error!
The balloons from yesterday's experiment were filled with hydrogen, carbon dioxide, oxygen, a mixture of hydrogen and oxygen, helium, and air. Use the facts below and your observations to determine which balloon is which.
Hydrogen (H2): D = .000089 g/mL,
Carbon Dioxide (CO2): .001977 g/mL
Oxygen (O2): D = .001331 g/mL
Helium (He): D = .00018 g/mL,
Air (Mixture, mostly N2): .00128 g/mL
Hydrogen: Very flammable
Carbon Dioxide: No
Oxygen: No, but provides fuel for fire
Nitrogen (N2): No
1. You are measuring length with a meter stick. However, you do not realize that the first 4.0 centimeters of the meter stick are missing. How will your measurements be with respect to precision and accuracy?
2. Write your own example of a scenario that would give you inaccurate but precise measurements.
3. Agree or disagree with the following statement and explain your choice: "We can never be 100% certain of any measurement because at some point we'll reach the limit of precision. After that, it is all just a guess."
2. How many significant figures does each number have?
1. Evaluate the accuracy and precision of classmate A and classmate B. (wait for demo)
Warm-Up: Quiz Practice
Write the following numbers using scientific notation.
Write out the following number in full:
5) 2.14 x 10^-5
Answer the following problems (watch your SIG FIGS)
6. 1.12 mL + 0.465 mL =
7. 1.111111 g x 2 g =
8. 100.0 cm - 70.05 cm =
1) 0.00000342 => 3.42 x 10^-6
2) 1,9800,000 => 1.98 x 10^7
3) 879,300,000 => 8.793 x 10^8
4) 0.000783 => 7.83 x 10^-4
5) 2.14 x 10^-5 => .0000214
6) 1.12 mL + 0.465 mL
= 1.585 mL => 1.59 mL
7) 1.111111 g x 2 g
= 2.2222222 g => 2 g
8) 100.0 cm - 70.05 cm =
= 29.95 => 30.0 cm
Many years ago in a land far, far away a King was given a crown that he doubted the authenticity of. The King asked a man by the name of Archimedes to help him determine whether the crown was truly made of gold. Archimedes knew that the ratio between mass and volume remained constant for a pure substance.
Welcome to Saguaro Chemistry!
Classification of Matter
Chemical Formulas & Equations
Chemical Bonding & Kinetics
Acids, Bases, Salts & Titrations
Mass = kilogram
Volume = cubic meter
Length = meter
Time = second
Electrical current = ampere
Temperature = Kelvin
Amount of substance = mole
Luminous intensity = candela
Density = kg/m^3
Kilo Hecto Deca (UNIT) Deci Centi Milli