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 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): m2
- Volume (length times 3): m3
- 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 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[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 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 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:
- 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 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]
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
More Practice[edit | edit source]
- 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
Percent Error[edit | edit source]
Expirmented Value - Accepted Value
___________________________________ • 100 = [ANSWER]
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.