**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**

A scientific

observation

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.

An

inference

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

Pure Science

Organic Chemistry

Inorganic Chemistry

Biochemistry

Physical Chemistry

Thermochemistry

Electrochemistry

Nuclear Chemistry

Applied Science

Medications

Smartphones

Internet

Agricultural Research

"Technology"

Problem

Research

Hypothesis

Experiment

Results

Conclusion

Define the problem (after observing a situation)

Research the problem

Past Experiments

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)

Collect Data

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

Theory

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

Law

Precision

Accuracy

The measurement can be repeatable by others. (All close to the same value)

Reliable

Repeatable

Reproducible

Someone else could use the same equipment and get the same measurement

Bunsen Burner

Wire Gauze

Bowl

Crucible Tongs

Test Tube Holder

Volumetric Flask

Crucible

Watch Glass

Ring Stand

Erlenmeyer Flask

Clay Triangle

Beaker

Test Tubes

Close to the accepted value

**Observation**

**Interpretation**

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.

**Significant Figures**

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

Add/Subtract

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

Multiply/Divide

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

Derived Units

A unit made through a calculation of measurements

Ex: Measure the mass and volume and you can calculate the density.

Metric/

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

Nano

Micro

Milli

Centi

Deci

Kilo

0.000,000,001

0.000,001

0.001

0.01

0.1

1000

1 billionth

1 millionth

1 thousandth

1 hundredth

1 tenth

1000 x larger

Scientific Notation

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.

**Dimensional Analysis**

(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.

Given

Want

Units Cancel

**Measuring Rules**

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)

Percentage Error

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

True Vale

x 100

Percentage Error vs.

Testing Percentage

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!

Graduated Cylinder

Buret

Warm-Up

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.

Densities

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

Flammable:

Hydrogen: Very flammable

Carbon Dioxide: No

Oxygen: No, but provides fuel for fire

Helium: No

Nitrogen (N2): No

Warm-Up Questions

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."

Warm-Up

2. How many significant figures does each number have?

A: 1,009.0

B: 0.000560

C: 4,300

D: 600,001

E: 5,600,320

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.

1) 0.00000342

2) 19,800,000

3) 879,300,000

4) 0.000783

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

Density Lab

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!

Mrs. Polson

(Stolen)

The Class

Science/Measurement

Classification of Matter

Atomic Structure

Periodic Table

Chemical Formulas & Equations

Solutions

Chemical Bonding & Kinetics

Thermodynamics

Acids, Bases, Salts & Titrations

Gas Laws

Oxidation-Reduction Reactions

Electrochemistry

**SI UNITS**

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

1000000

.000001

Metric Units