Chemistry Test 1

scientific method

scientific method

a systematic approach used in scientific study to do research or verify the work of others

qualitative data

info that describes a physical characteristic of a subject; ex. color, taste, smell, feel

quantitative data

measured, numerical info that describes as subject; ex. length, mass, density, speed

experiment

a set of controlled observations that test the hypothesis

control

the standard used for comparison

independent variable

the variable the experimenter plans to change

dependent variable

the variable whose value depends on the changed variable

constants

variables that should be kept the same across both control and experimental groups

scientific law

a statement about how some aspect of the natural world behaves

scientific theory

an explanation of some aspect of the natural world; may accompany a law explaining them

basic science

research aimed at understanding fundamental problems; provides the knowledge foundation for applied science

applied science

the application of basic science knowledge to solve practical problems

matter

anything that has mass and takes up space; particles are always in motion; the kinetic energy of the particles increases as temp increases;

temperature

a measure of average kinetic energy

solid

particles vibrate in place (don’t move past each other), definite shape, definite volume

liquid

molecules slide past each other (fluid), indefinite shape, definite volume (still has the same amt as before)

gas

molecules separate and move throughout the container (they can collide), indefinite shape, indefinite volume (they can expand)

plasma

particles collide into charged particles (±) and gain or lose electrons, indefinite shape, variable volume

vapor

the gaseous phase of a substance that exists as a solid or liquid at room temp (ex. water vapor)

physical property

can be observed without changing the identity of the substance (ex. density, color, melting point); can observe with the five senses

chemical property

describes the ability of a substance to undergo changes in identity; must fundamentally change the substance to observe the property (ex. flammable, reacts with…)

extensive property

depends on the amt of matter present (ex. volume, mass)

intensive property

depends on the identity of the substance, NOT the amount (ex. boiling pt, density) - the boiling point is always 100 degrees Celsius

physical change

changes without changing chemical composition (ex. ripping paper, water on paper, dissolving, breaking glass, any type of phase change)

chemical change

changed the chemical composition of a substance (ex. when molecules are rearranged, burning, rusting, some type of reaction)

signs of chemical change

change in color, evolution of a new gas, spontaneous evolution of heat or light, evolution of an odor, formation of a precipitate (solid “falls out” of a liquid)

chemical reaction

also known as a chemical change

law of conservation of matter

how much you start with = how much you end with; mass of reactants = mass of products (matter cannot be created or destroyed)

pure substance

matter with uniform and constant composition (elements and compounds); unique chemical and physical properties

mixture

combinations of 2 or more pure substances; each substance retains its individual properties; variable composition (can differ by amount); can be separated by physical means

heterogeneous mixture

uneven blend of 2 or more pure substances; individual substances remain distinct (ex. sand and water, chocolate chip cookies)

homogeneous mixture

even blend of 2 or more substances; uniform composition; very small particles that don’t settle (ex. apple juice)

filtration

uses a porous barrier to separate a solid from a liquid

distillation

based on differences in the boiling points of the substances involved

chromatography

based on the ability of a substance to travel or be drawn across a surface

element

pure substances that cannot be separated into simpler substances by physical or chemical means

compound

substances that contain 2 or more elements chemically combined in fixed proportions; can be separated by a chemical change; properties differ from those of individual elements

law of definite proportions

A compound is always composed of the same elements in the same portion by mass

percent by mass

what the relative amounts of elements in a compound are expressed as (has an equation)

law of multiple proportions

sometimes, 2 elements can combine in more than one way to form different compounds

kelvin

SI base unit for temperature; equals Celsius + 273

derived unit

combination of base units

volume

length x length x length (1cm³ = 1mL)

density

equals mass over volume (g/cm³ or g/mL)

dimensional analysis

a problem solving method to convert between units by multiplication, division, and cancelling units out top to bottom

accuracy

how close a measurement is to the accepted value (measured with percent error); correctness

precision

how close a series of measurements are to each other (measured with range); consistency

percent error

measure for how accurate values are from a literature (accepted) value

range

the highest value in a data set minus the lowest value in a data set

are

fill in the blank: nonzero numbers ___ always significant (are/are not)

are

fill in the blank: zeros between nonzero numbers ___ always significant (are/are not)

are

fill in the blank: all final zeros to the right of the decimal ___ significant (are/are not)

are not

placeholder zeros ___ significant (are/are not)

have

fill in the blank: counting numbers and defined constants ____ infinite number of sig figs (have/ do not have)

addition and subtraction

when doing sig figs, you round your answer to the last common place in…

multiplication and division

when doing sig figs, you round your answer to the least number of sig figs in….