# High School Chemistry/Introduction to Methods of Chemistry

Chemistry is the study of the composition of matter, which is anything with mass and volume. They're five major branches of chemistry:
* Organic Chemistry: All substances containing the element: carbon (all living things, fuels).
* Inorganic Chemistry: All substances inorganic (not containing carbon {But Carbon compounds such as carbides (e.g., silicon carbide [SiC2]), some carbonates (e.g., calcium carbonate [CaCO3]), some cyanides (e.g., sodium cyanide [NaCN]), graphite, carbon dioxide, and carbon monoxide are classified as inorganic}).
* Analytical Chemistry: Separate and identify matter (drug testing).
* Physical Chemistry: Behavior of chemicals (why does nylon stretch?/reactions).
* Biochemistry: Chemistry of living organisms (photosynthesis, metabolism, respiration).

### Measurements and Data Collection

* Can be quantitative (numerical) or qualitative (subjective).
[qualitative deals with odor, color, and texture]
* Must be...:
** Accurate: How close your measurements are close to the known value.
** Precise: Measurements are simply close to each other through repeated trials.
** Easy to communicate

### Metric System and International System of Measurement

* Allows for scientists to easily communicate data and results.
* Based on standard units (SI units)
** Length (meters (m))
** Mass (kilogram (kg))
** Temperature (Kelvin (K)) [K = Celsuis + 273]
** Time (seconds (s))
** Amount of a substance (moles (moL))

#### Derived Units

Combination of two regular units:
* Area (length times 2): m$^2$
* Volume (length times 3): m$^3$
* Density: ${\tfrac {mass}{volume}}$
* Speed: meters per second (m/s)

### Scientific Notation

* Many measurements in science involve very small or very large numbers.
* Scientific notation is an easy way to express either.
* Format: Coefficient x 10$^{exponent}$
* Coefficient is a number between 1 and 9. If the exponent is positive, its a big number, while if it negative, its a small number.

### The SI (Metric) System Continued

* Another way scientists express very large/small numbers.
* The metric system uses universal units for ease of communication and prefixes to make huge/tiny numbers more manageable

#### Deka (da) 10 [1 x 10$^1$]

BASE UNIT (grams, liters, meters, seconds, moles) ↑ Bigger ↓ Smaller

#### Pico (p) 1,000,000,000,000 [1 x 10$^{-12}$]
### Uncertainty in Measurement

* There's ALWAYS some error in taking measurements because instruments were made by people and are used by people.
* This is one reason for the need for repeated trials in science.
* Even so, in EVERY measurement there's always at least 1 uncertain digit (always the last one).
* So, you always measure to the place you know for sure, plus one more (in other words, one place past the scale of the instrument).

### Signifcant Figures/Digits

It would be tough if we had to report uncertainty every time, so we use significant figures (sig figs). The number of sig figs in a measurement, such as 2.531, is equal to the number of digits that are known with some degree of confidence. When you take a measurement, you'll use the same technique as above and omit the +/-. The number of sig figs in your measurement depends on the scale of the instrument.
As we improve the sensitivity of the equipment used to make a measurement, what do you think happens to the number of sig figs? Increases.

### Counting Significant Figures

* Always count nonzero digits:
** 21
** 8.926
* Never count leading zeros:
** 034
** 0.091
* Always count zeros which fall somewhere between 2 nonzero digits:
** 20.8
** 00.1040090
* Count trailing zeros if and only if the number contains a decimal point:
** 210
** 210000000
** 210.0
** 25000.
* For numbers expressed in scientific notation, ignore the exponent:
** -4.2010 x 10$^{28}$

### Calculating and Rounding using Significant Figures

Usually, experiments/measurements are repeated to ensure precision. To report results, we usually take an average of data. So, how do you know where to round? We'll see:
NOTE: Your calculation can be no more specific than the LEAST specifics of your original measurements/numbers.

### Rounding Rules to Memorize
#### Addition/Subtraction

Round to the least number of sig figs after the decimal point
* 25.6 + 85.379 + 145.69 = 256.669
       ROUNDED ANSWER: 256.700

#### Multiplication/Division

Round to the least number of sig figs TOTAL
* 52.0 x 365 x 13 = 246,000
       ROUNDED ANSWER: 250,000

#### More Practice

* 37.2 + 18.0 + 380 = 435.2
       ROUNDED ANSWER: 435.
* 0.57 x 0.86 x 17.1 = 8.38242
       ROUNDED ANSWER: 8.4
* (8.13 x 10$^{14}$) / (3.8 x 10$^2$) = 2.139473684 x 10$^{12}$
       ROUNDED ANSWER: 2.1 x 10$^{12}$

## Percent Error

Expirmented Value - Accepted Value ___________________________________ • 100 = [ANSWER] Accepted Value

## Calculating Average Atomic Mass

(amu1 • abd1) + (amu2 • abd2) = average atomic mass [of the element]
* ABD = Abundance
For the percentages, move the decimal two places to the left.