High School Chemistry/Introduction to Methods of Chemistry
Chemistry is the , 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 CollectionEdit
- 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 MeasurementEdit
- 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))
Combination of two regular units:
- Area (length times 2): m2
- Volume (length times 3): m3
- Speed: meters per second (m/s)
- 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 ContinuedEdit
- 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]
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 MeasurementEdit
- 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).
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 FiguresEdit
- Always count nonzero digits:
- Never count leading zeros:
- Always count zeros which fall somewhere between 2 nonzero digits:
- Count trailing zeros if and only if the number contains a decimal point:
- For numbers expressed in scientific notation, ignore the exponent:
- x 1028
Calculating and Rounding using Significant FiguresEdit
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 MemorizeEdit
Round to the least number of sig figs after the decimal point
- 25. + 85. + 145. = 256.69
- ROUNDED ANSWER: 256.700
Round to the least number of sig figs TOTAL
- x x = 6,000
- ROUNDED ANSWER: 250,000
- 37. + 18. + 380 = 435.2
- ROUNDED ANSWER: 435.
- 0. x 0. x = 8242
- ROUNDED ANSWER: 8.4
- ( x 1014) / ( x 102) = 39473684 x 1012
- ROUNDED ANSWER: 2.1 x 1012
Expirmented Value - Accepted Value
___________________________________ • 100 = [ANSWER]
Calculating Average Atomic MassEdit
(amu1 • abd1) + (amu2 • abd2) = average atomic mass [of the element]
- ABD = Abundance
For the percentages, move the decimal two places to the left.