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Some online homework discussion

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You log on to the MyLabsPlus website
- Go to assignments
  - They are arranged in order
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  - They are due at midnight, but you get 1% per hour late off your score. So you aren’t SOL if you don’t get it right on time
  - You get a drop on the homework
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  - Speech about tax returns is actually about:
    - You have 5 freebies on the clicker questions
      - absences
    - Same is true for the lab
      - You get 2 absences
        
        More starts penalties
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  - Re-iterating
    - You get one drop grade in the class
      - Shoot to make it the last test because it is the hardest
- Pre-labs are due mid-day the day before your lab
  - If you have a Monday lab, your pre-lab is due noon Sunday
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- You have two attempts at getting multiple choice right in homework
- 6 on numeric

Chapter 1 Notes Part 2

Classification of Pure Substances

Pure substances can be categorized into two types:
- Elements
- Compounds
This categorization depends on whether or not they can be broken down (or decomposed) into simpler substances.
An element is a substance that cannot be chemically broken down into simpler substances.
- Basic building blocks of matter
- Composed of single type of atom, like helium
A compound is a substance composed of two or more elements in fixed definite proportions.
Most elements are chemically reactive and combine with other elements to form compounds.

Heterogeneous Mixture

A heterogeneous mixture is one in which the composition varies from one region of the mixture to another.
- Made of multiple substances, whose presence can be seen (example: a salt and sand mixture)
  - Portions of a sample of a heterogeneous mixture have different composition and properties.

Homogeneous Mixture

A homogeneous mixture is one made of multiple substances, but it appears to be one substance.
All portions of a sample have the same composition and properties (like sweetened tea).
Homogeneous mixtures have uniform compositions because the atoms or molecules that compose them mix uniformly.

The Scientific Approach to Knowledge

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The approach to scientific knowledge is empirical
It is based on observation and experimentation.
The scientific method is a process for understanding nature by observing nature and its behavior through experimentation.
Key characteristics of the scientific method
- Observations
- Formulation of hypotheses
- Experimentation
- Formulation of laws and theories

Observations

Observations:
- They are also known as data.
- They are the descriptions about the characteristics or behavior of nature.
Observations, verification of observations, and experimentation can lead scientists to formulate a hypothesis.

The Scientific Approach to Knowledge

Scientists try to understand the universe through empirical knowledge gained through observation and experiment

Gathering Empirical Knowledge ─ Observation

Some observations are descriptions of the characteristics or behavior of nature ─ qualitative
Some observations compare a characteristic to a standard numerical scale ─ quantitative

From Observation to Understanding

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Hypothesis – a tentative interpretation or explanation for an observation
A good hypothesis is one that can be tested to be proved wrong!

Testing Ideas

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Ideas in science are tested with experiments
An experiment is a set of highly controlled procedures designed to test whether an idea about nature is valid
The experiment generates observations that will either validate or invalidate the idea

Is this a good hypothesis?

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Yesterday, the phase of the moon was a crescent. I observed that it rained a lot yesterday.
It also rained during the previous crescent moon.
I hypothesize that crescent moons cause rain showers
- The hypothesis is the ‘why?’
My answer: This is a good hypothesis because it can be tested and proved wrong
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Best answer: C
- It’s a good hypothesis because it’s falsifiable
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- Good reasons to understand the importance of hypothesis

From Specific to General Understanding

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A hypothesis is a potential explanation for a single or small number of observations
A scientific theory is a general explanation for why things in nature are the way they are and behave the way they do
- Integrates a lot of different observations
- Lets us predict what’s happening in the universe

Think about it

Given what you just learned about the term “Theory”, what’s wrong with this statement:
- “The theory of gravity is just a theory and therefore probably wrong”
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  - By the time you get to calling things theories, they have been tested a lot
    - The scientific method says you can’t prove anything, you can only disprove things
    - You’ll have to explain exceptions to the theory at some point so a new theory will emerge

From Specific to General Observations

A scientific law is a statement that summarizes all past observations and predicts future observations
- Law of Conservation of Mass – “In a chemical reaction matter is neither created nor destroyed.”
A scientific law allows you to predict future observations
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Relationships Between Pieces of the Scientific Method

The Scientific Approach to Knowledge

It is necessary to be careful with the information presented by an experimentalist who lacks theoretical principles… [he] gathers at random several facts and presents them as proofs… scientific knowledge without reasoning [theory] does not exist.”
- J. le R. d’Alembert (1717-1783), from Nouvelles Experiences sur la Resistance des Fluids. Jombert, Paris (1997)
D’Alembert was always surrounded by controversy. ….Unfortunately he carried [his]… pugnacity into his scientific research and once he had entered a controversy, he argued his cause with vigour and stubbornness. He closed his mind to the possibility that he might be wrong…
- Thomas L. Hankins (1990). Jean D’Alembert: Science and the Enlightenment. Taylor & Francis. p. 236. ISBN 2881243991

Why Is Scientific Measurement Important?

Scientific data can be either qualifiable or quantifiable
- Qualifiable data are observational
  - Subjective in nature
  - Examples: color, shape
Quantifiable data are measurable (empirical).
- Objective in nature
- Uses equipment (e.g., glassware, balance, instrumentation) capable of generating empirical data with standardized UNITS.
  - English system (e.g., inch, feet, etc.) – International System of Units (SI)
  - Metric system

What Is a Measurement?

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quantitative observation
comparison to an agreed- upon standard
every measurement has a number and a unit

Significant Figures

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No measurement can be more accurate than half the smallest division
- Note: Tro says 1/10 of smallest division
Often write +- to indicate this: 11+-1 mm, 1.1 +-0.3 cm
No error range given? Then assume + half the least Significant Figure
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Any digit that is not zero is significant
- 1.234 kg 4 significant figures
Zeros between nonzero digits are significant
- 606 m 3 significant figures
Zeros to the left of the first nonzero digit are not significant
- 0.08 L 1 significant figure
If a number is greater than 1, then all zeros to the right of the decimal point are significant
- 2.0 mg 2 significant figures
If a number is less than 1, then only the zeros that are at the end and in the middle of the number are significant
- 0.004020 g 4 significant figures
test your ability

How many significant figures are in each of the following measurements?

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24 mL
- 2
3001 g
- 4
0.0320 m^3
- 3
6.4 x 104 molecules
- 2
560 kg
- 2

Rounding Rules for Significant Figures

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Digit being rounded > 5
- Add 1 to least significant digit
- Result: 4.16 with 2 sig figs becomes 4.2
Digit being rounded < 5
- Result: 4.14 with 2 sig figs becomes 4.1
ROUND AT THE END OF THE PROBLEM

Addition or Subtraction - Significant Figures

The answer cannot have more digits to the right of the decimal point than any of the original numbers
- - 1.1 has one sig fig after decimal
  - round 90.432 to 90.4
Look at sig figs in the given variables in the problem and have that many in your answer

Vocab

Term	Definition
element	a substance that cannot be chemically broken down into simpler substances
compound	a substance composed of two or more elements in fixed definite proportions
heterogeneous mixture	mixture in which the composition varies from one region of the mixture to another
homogeneous mixture	mixture made of multiple substances, but it appears to be one substance
observations	also known as data
hypothesis	a tentative interpretation or explanation for an observation
qualitative	type of observation which describe characteristics of something
quantitative	type of observation which are compare a characteristic to a standard numerical scale
experiment	a set of highly controlled procedures designed to test whether an idea about nature is valid
scientific theory	a general explanation for why things in nature are the way they are and behave the way they do
scientific law	a statement that summarizes all past observations and predicts future observations
Law of Conservation of Mass	In a chemical reaction matter is neither created nor destroyed