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:
 * 1) Organic Chemistry: All substances containing the element: carbon (all living things, fuels).
 * 2) 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}).
 * 3) Analytical Chemistry: Separate and identify matter (drug testing).
 * 4) Physical Chemistry: Behavior of chemicals (why does nylon stretch?/reactions).
 * 5) 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): m2
 * Volume (length times 3): m3
 * 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 10exponent
 * 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
BASE UNIT (grams, liters, meters, seconds, moles) ↑ Bigger ↓ Smaller
 * 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 1012]
 * Giga (G) 1,000,000,000 [1 x 109]
 * Mega (M) 1,000,000 [1 x 106]                           ← x's bigger than
 * Kilo (K) 1000 [1 x 103]
 * Hecto (h) 100 [1 x 102]
 * Deka (da) 10 [1 x 101]
 * 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

 * 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

 * 1) Always count nonzero digits:
 * 2) * 21
 * 3) * 8.926
 * 4) Never count leading zeros:
 * 5) *0 34
 * 6) *0.0 91
 * 7) Always count zeros which fall somewhere between 2 nonzero digits:
 * 8) * 20.8
 * 9) *00. 1040090
 * 10) Count trailing zeros if and only if the number contains a decimal point:
 * 11) * 21 0
 * 12) * 21 0000000
 * 13) * 210.0
 * 14) * 25000.
 * 15) For numbers expressed in scientific notation, ignore the exponent:
 * 16) * -4.2010 x 1028

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
Round to the least number of sig figs after the decimal point
 * Addition/Subtraction
 * 25. 6 + 85. 379 + 145. 69 = 256. 6 69
 * ROUNDED ANSWER: 256.700

Round to the least number of sig figs TOTAL
 * Multiplication/Division
 * 52.0 x 365 x 13 = 24 6,000
 * ROUNDED ANSWER: 250,000

More Practice

 * 37. 2 + 18. 0 + 380 = 435.2
 * ROUNDED ANSWER: 435.


 * 0. 57 x 0. 86 x 17.1 = 8.3 8242
 * ROUNDED ANSWER: 8.4


 * ( 8.13 x 1014) / ( 3.8 x 102) = 2.1 39473684 x 1012
 * ROUNDED ANSWER: 2.1 x 1012

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.