Chapter 2 Matter and Change

Units of Measurement SI Base Units Length (l) – meter (m) Mass (m) – kilogram (kg) Time (t) – second (s) Temperature (T) – Kelvin (K) Amount of substance (n) – mole (mol) Electric Current (I) – ampere (A) Measurements are agreed upon values representing some quantity SI Measurements Scientists agreed on a single system of measurements Le Systeme International d’Unites (SI) All other SI Units are derived (they come from combining other units)

Derived SI Units Area (A) (m2) l x w Volume (V) (m3) l x w x h Density (D) (kg/m3) M/V Molar mass (Mm) (kg/mol) mass / moles Molar Volume (Vm) (m3/mol) Volume / moles Energy (E) (J) joule Force x length

Conversion Factors Dimensional Analysis A ratio used to compare one unit of measure to another unit of measure of equal value 1 ft = 12 in 1 kg = 1000 g 1 L = 1000 mL Dimensional Analysis A mathematical technique using conversion factors to solve problems

Density Density is a physical property of matter used to help identify a substance Used in chemistry as an easy way to identify substances Density = Mass / Volume D = M / V Density of water is 1 g/ml More dense things sink, less dense floats

Using Scientific Measurements Accuracy Refers to the closeness of measurements to the correct or accepted value Precision Refers to the repeatability of the measurements to the same measurement

Percent Error A method of showing accuracy in measurements Negative value says accepted value is greater than experimental Measured value is sometimes referred to as experimental value True value is sometimes referred to as accepted value

Comparing Measurements Directly Proportional If one value goes up the other value also goes up at a constant rate. Appears as a straight line on a graph Inversely Proportional If one value goes up the other value also goes down at a constant rate. Appears as a curved line (hyperbola) on a graph