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Chem 111 Ch. 1

scientific method 1. carefully define the problem; 2. perform experiments, make careful observations, and record information about the system (data); 3. interpretation - attempt to explain the observed phenomenon; observation --> representation --> interpretation
qualitative data general observations about the system (the part of the universe that is under investigation)
quantitative data numbers obtained by various measurements of the system (the part of the universe that is under investigation)
hypothesis a tentative explanation for a set of observations
law a concise verbal or mathematical statement of a relationship between phenomena that is always the same under the same conditions (Newton's second law of motion, i.e. F=ma)
theory a unifying principle that explains a body of facts and/or those laws that are based on them
matter anything that occupies space and has mass
chemistry the study of matter and the changes it undergoes
substance matter that has a definite or constant composition and distinct properties (water, table salt-sodium chloride, carbon dioxide, i.e.); can be either an element or a compound
mixture a combination of two or more substances in which the substances retain their distinct identities (air, soft drinks, milk, cement, i.e.)
homogeneous mixture the composition of the mixture is the same throughout the solution (spoonful of sugar dissolved in water after sufficient stirring)
heterogeneous mixture the composition of the mixture is not uniform (sand grains mixed with iron fillings - grains/fillings remain visible and separate; oil & water - the liquid doesn't have a constant composition)
element a substance that cannot be separated into simpler substances by chemical means
compound a substance composed of two or more elements chemically united in fixed proportions (water, i.e. is made up of 2 parts hydrogen and 1 part oxygen no matter where it comes from);can only be separated by chemical means into their pure components
physical property can be measured and observed without changing the composition or identity of a substance (melting point measured when ice melts into water - differ only in appearance and not composition)
chemical property any property of a substance that cannot be studied without converting the substance into some other substance (hydrogen gas forms water when it burns in air - chemical property of hydrogen; hard-boil an egg - changes chemical makeup as well as physical)
extensive property depends on how much matter is being considered (mass, length, and volume; more matter = more mass)
intensive property does not depend on the amount of matter being considered (temperature - two beakers of water at same room temp: if combined, temperature will not change)
macroscopic properties can be determined directly (length, volume, mass, etc.)
microscopic properties on the atomic or molecular scale, must be determined by an indirect method (chemical composition, i.e.)
tera-; giga-; mega-; kilo-; deci-; centi-; milli-; micro-; nano-; pico- (T) 1 x 10^12; (G) 1 x 10^9; (M) 1 x 10^6; (k) 1 x 10^3; (d) 1 x 10^-1; (c) 1 x 10^-2; (m) 1 x 10^-3; (ยต) 1 x 10^-6; (n) 1 x 10^-9; (p) 1 x 10^-12
mass measure of the quantity of matter of an object
weight the force that gravity exerts on an object
density mass/volume (g/cm^3)*intensive property - does not depend on the quantity of matter present because it's a ratio of the two quantities
kelvin the absolute temperature scale (0 K is the lowest temperature - there are no neg. values on this scale)
scientific notation: addition/subtraction & multiplication/division N x 10^n - addition/subtraction: n1 must = n2. then add/subtract N1 & N2. n remains the same and equal; multiplication/division: multiply/divide N1 & N2 as usual, either add/subtract n1 & n2 (for multiplying/dividing, respectively)
significant figures 1. any digit that is not zero is significant; 2. zeros btw. nonzero digits are significant; 3. zeros to the left of the first nonzero digit are not significant (.0000345 = 3 s.f.); 4. if a number is > 1, the zeros to the right of the decimal are sig.
sig figs: addition/subtraction & multiplication/division addition/subtraction: only pay attention to the #'s to the right of the decimal - 25.01 + 2.1 = 27.1 NOT 27.11; multiplication/division: go by lowest # of sig figs in original - 25.55 / 2.0 = 6.3 NOT 6.275
accuracy tells us how close a measurement is to the true value of the quantity that was measured (average may give a high accuracy, so must look at precision, too)
precision refers to how closely two or more measurements of the same quantity agree with one another (think of a dart board)
Created by: court52