# 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, feuls).**Inorganic Chemistry**: All substances inorganic (not containing carbon).**Analytical Chemistry**: Separate and identify matter (drug testing).**Physical Chemistry**: Behavior of chemicals (why does nilon stretch?/reactions).**Biochemistry**: Chemistry of living organisms (photosynthesis, metabolism, respiration).

### Measurements and Data Collection[edit | edit source]

- Can be
**quantitiative**(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[edit | edit source]

- 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[edit | edit source]

Combination of two regular units:

- Area (length times 2): m
^{2} - Volume (length times 3): m
^{3} - Density:
- Speed: meters per second (m/s)

### Scientific Notation[edit | edit source]

- 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[edit | edit source]

- 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

- Tera (T) 1,000,000,000,000 [1 x 10
^{12}] - Giga (G) 1,000,000,000 [1 x 10
^{9}] - Mega (M) 1,000,000 [1 x 10
^{6}] ← x's bigger than - Kilo (K) 1000 [1 x 10
^{3}] - Hecto (h) 100 [1 x 10
^{2}] - Deka (da) 10 [1 x 10
^{1}]

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

- Deci (d) 10 [1 x 10
^{-1}] - Centi (c) 100 [1 x 10
^{-2}] - Milli (m) 1000 [1 x 10
^{-3}] - Micro (µ) 1,000,000 [1 x 10
^{-6}] ← x's smaller than - Nano (n) 1,000,000,000 [1 x 10
^{-9}] - Pico (p) 1,000,000,000,000 [1 x 10
^{-12}]

### Uncertainty in Measurement[edit | edit source]

- 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[edit | edit source]

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[edit | edit source]

- 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}

- -4.2010 x 10

### Calculating and Rounding using Significant Figures[edit | edit source]

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[edit | edit source]

- 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[edit | edit source]

- 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[edit | edit source]

Expirmented Value - Accepted Value

___________________________________ • 100 = [ANSWER]

Accepted Value

## Calculating Average Atomic Mass[edit | edit source]

(amu1 • abd1) + (amu2 • abd2) = average atomic mass [of the element]

**ABD**= Abundance

For the percentages, move the decimal two places to the left.