Examination 1 Review
The best place to begin study is with the notes you have taken in class. More detailed information about topics that are still causing confusion can typically be found in the textbook.
Nature of Science
- Reproducible
- An implicit assumption of all science is that a set of unchanging, physical laws exist that control the behavior of the world around us. For example, we assume that a falling object will not stop falling for no reason, water will freeze at around 32 F, a burning fire will give off heat, etc.
- Operational/Process Science
- Based on the Scientific Method.
After enough applications of this cycle, a hypothesis can turn into a theory and a theory can turn into a law. - Historical Science
- Examines events that have already happened. Cannot use the scientific method because we cannot do experiments on past events. While some experiments can often be done, the actual events of the past cannot be reproduced in the lab. For example, we cannot create another universe to see if the 'Big Bang' really did or did not occur.
Relative Risk
While there are many possible ways to attempt to quantify 'risk', we will use the following equation:
Relative Risk = (% effect in active group) / (% effect in control group)
For an example of how to apply this equation, consider the following hypothetical data:
'Itchy palms' were identified as a serious problem that could be investigated. In an attempt to 'cure' this, 100 randomly-selected people were given the drug 'No-ItchP'. In this group, 8 developed 'itchy palms'. A second group of 50 people were given hand creme that did not contain 'No-ItchP'. In this group, only 5 people developed 'itchy palms'.
Summarizing this data in tabular form gives:
| Got itchy palms | No symptoms | Total # in group | |
| Received 'No-ItchP' drug | 8 | 92 | 100 |
| Didn't get drug | 5 | 45 | 50 |
When analyzing this data, the following results were obtained:
| 8 | 5 | |||||
| % effect(active) = | ----- | = 0.08 or 8.0% | % effect(control) = | ----- | = 0.10 or 10.0% | |
| 100 | 50 |
From these values, the relative risk is calculated to be:
| 0.08 | ||
| Relative Risk = | ----- | = 0.80 |
| 0.10 |
Values of Relative Risk between 0.75 and 1.25 are generally considered to be a weak correlation. (A value of 1.0 indicates no difference). Ideally, the Relative Risk should either be less than 0.50 or more than 2.0 to suggest a meaningful relationship.
Scientific (Exponential) Notation
Scientific notation is a convenient way of representing very large or very small numbers. It is easier to write that there are 6.02 x 1023 atoms in 18 grams of water than to write that there are 602,000,000,000,000,000,000,000 atoms in 18 grams of water.
Converting to and from scientific notation into the decimal system is simply a matter of moving the decimal point and multiplying by the appropriate power of ten. In scientific notation, the first number will typically be >= 1 and <10. So to convert a number like 12,345 into scientific notation, the first part becomes 1.2345. Obviously, 1.xx is less than 12,xxx, so we will need to multiply 1.2345 by something. The "something" will be 10?. In order to determine the exponent (the number to use in place of the ?), simply count the number of positions the decimal point moved. If you made the number smaller (12,xxx -> 1.2xxx), then the exponent will be positive. If you make the number larger, the exponent will be negative. So in our example, the exponent is +4. In scientific notation, 12,345 = 1.2345 x 10+4. Additional examples are shown in the table below.
| Decimal | Scientific Notation | Comments |
| 5280 | 5.280 x 10+3 | Big decimal # means larger, positive exponent |
| 0.062 | 6.2 x 10-2 | Small decimal # means negative exponent |
| 0.000000000154 | 1.54 x 10-10 | (Typical distance of a carbon-carbon bond.) Smaller value means exponent will be more negative. |
Units of Measure
Observation is a crucial component of the scientific method. For many phenomena, measurements provide a means of "putting a number on" or "quantifying" an observation (how much liquid was produced, how hot did it get, ...). Most measurements are based on some arbitrary standard. There is nothing inherently better about either a foot or a meter or a cubit or any other length. What makes a unit of length useful is reproducibility. A foot is a useful unit of measure because "everyone" accepts that a foot is a certain length. Scientists tend to use the metric system not because it is any better than any other system, but because it is accepted as a convenient standard by most of the scientific community.
The primary advantage of the metric system is that it is based on powers of 10. A small number of base units (such as meter or gram) are defined, then different fractions or multiples of a given base unit are indicated by adding a prefix in front of the name of the base unit. Look at the following comparison of the "American" system with the metric system for length and volume.
| Length | 12 inches = 1 foot | 3 feet = 1 yard | 5280 feet = 1 mile |
| 10 millimeter = 1 centimeter | 100 centimeter = 1 meter | 1000 meter = 1 kilometer | |
| Volume | 2 cups = 1 pint | 2 pints = 1 quart | 4 quarts = 1 gallon |
| 10 milliliter = 1 centiliter | 100 centiliter = 1 liter | 1000 liter = 1 kiloliter |
Note the consistency of the names in the metric system. 10 milli-anything = 1 centi-anything, etc. The prefix indicates how many orders of magnitude (powers of ten) the unit is away from the base unit. The following table summarizes some of the more common prefixes.
| Prefix | Size | Sci. Not. | Explanation | Example |
| kilo | 1000 | 10+3 | 3 orders of magnitude larger than base unit | 1 kilometer = 1000 meters |
| – | 1 | 100 | (same size as base unit) | 1 meter = 1 meter |
| deci | 1/10 | 10-1 | 1 orders of magnitude smaller than base unit | 10 decimeters = 1 meter |
| centi | 1/100 | 10-2 | 2 orders of magnitude smaller than base unit | 100 centimeters = 1 meter |
| milli | 1/1000 | 10-3 | 3 orders of magnitude smaller than base unit | 1000 millimeters = 1 meter |
| micro | 1/1,000,000 | 10-6 | 6 orders of magnitude smaller than base unit | 1,000,000 micrometers = 1 meter |
Metric vs. English units
The metric system often appears confusing to American students due to the fact that considerable effort is often made in making very accurate conversions between the two sets of units. In many cases, this is unnecessary. The following table lists some very approximate equivalences between the two sets of units. More exact conversions can be found in any standard textbook.
| English unit | Approximate Metric equivalent |
| yard | meter |
| inch | 2.5 centimeters |
| 10 miles | 16 kilometers |
| quart | liter |
| 2 pounds | 1 kilogram |
| ounce | 30 grams |
Classification of Matter
Physical Separation Techniques
The above diagram indicates that a mixture can be physically separated into pure substances without changing the chemical nature of the substances. In some cases, this separation is quite easy, while in other cases it might be extremely difficult. The following is a very incomplete list of some of the separation techniques that are often employed to separate mixtures.
| Technique | Example |
|---|---|
| Evaporation | Drying clothes on a clothesline |
| Distillation | Separation of components in crude oil |
| Solvent Extraction | Decaffeination of coffee |
| Filtration | In brewing of coffee, used to remove coffee grounds |
| Chromatography | Analysis of complex mixtures (drug testing, etc.) |
Chemical vs. Physical Changes
While both chemical and physical techniques can be used to modify a substance, these are quite different processes.