Chemistry 131 Chapter 2 Measurement Problem Solving and the Mole Concept 2 1 The Metric Mix Up A 125 Million Unit Error Quantification is the assignment of a number to some property of a substance or thing ex a 16cm pencil On Dec 11 1998 NASA launched the Mars Climate Orbiter A unit mix up caused the Orbiter to enter Mars atmosphere at an altitude too low Instead of orbiting it disintegrated costing 125mill 2 2 The Reliability of a Measurement The reliability of a measurement depends on the instrument used to make the measurement a butcher scale is more precise than a bathroom scale more digits more certainty less digits less certainty Scientific measures are reported so that every digit is certain except for the last which is estimated 5 213 certain estimated The number of digits reported depends on the measuring device 10 5g on one scale is 10 4977 on another There are two kinds of certainty in science 1 Accuracy how close the measurement is to the actual value 2 Precision how close a series of measurements are to one another 2 3 Density The density of a substance is the ratio of its mass m to volume v Density Mass Volume Density is an intensive property of a substance it is independent of the amount of the substance Mass is an extensive property of a substance it is dependent of the amount of the substance SI unit for density kg m3 Density is often displayed as g cm3 or gmL 2 4 Energy and Its Units Two fundamental components of the universe are matter and energy Energy is the capacity to work Work is an action of force through a distance The total energy of an object is the sum of its kinetic energy energy associated with its motion and its potential energy energy associated with its position composition Thermal energy is a type of kinetic associated with the temperature of an object Potential Energy Kinetic Energy Thermal Energy Principles of Energy Energy is neither created nor destroyed The tendency of systems with high potential energy to change in a way that lowers their potential energy Objects or systems with high potential energy tend to be unstable Chemical potential energy arises primarily from electrostatic forces between the electrically charged particles protons electrons that compose atoms and molecules The structure of a molecule determines the potential energy To Find Kinetic Energy KE 1 2mv2 The SI unit of mass m is kg and velocity v is m s The SI unit of energy is kg m2 s2 joule J One joule is very small so kJ is often used Another unit of energy is the calorie 1 kJ 1000 J 1 cal 4 184 J 1 Cal 1000 cal Not to be confused with the nutritional Calorie uppercase C The transfer of energy is always from the point of view of the system under observation ex dropping a weight system weight falling loses energy to its surroundings anything with which the system interacts When the system loses energy Exothermic When the system gains energy Endothermic 2 5 Converting Between Units Dimensional Analysis using units as a guide to solve problems Conversion Factor fractional quantity with units you are converting from on the bottom and units you are converting to on the top given unit desired unit givenunit desired unit 2 6 Problem Solving Strategies To Solve Any Problem Identify the starting point the given information Identify the end point what must be found Devise a way to get from start to end the conceptual plan Units Raised to A Power Remember to raise both the number and unit to the power 2 54cm 1in 2 54 cm 2 2 7 Solving Problems Involving Equations A conceptual plan is used to show how the equation takes us from the given start quantities to the find end quantities 6 45 cm2 1 2 d m v 2 8 Atoms and the Mole How Many Particles The Mole a mole mol is the amount of material containing 6 02214 1023 particles 1 mol 6 02214 1023 particles Avogadro s Number One mole of anything is 6 02214 1023 units of that thing usually rounded to 6 022 1023 The value of the mole is equal to the number of atoms in exactly 12g of pure carbon 12g C 1 mol 6 022 1023 C atoms Number of Moles and Number of Atoms Conversion 1mol atoms 6 022 1023atoms or 6 022 1023atoms 1mol atoms Mass and Amount Number of Moles Conversion To count atoms by weighing them mass is needed The mass of 1 mol of atoms is the molar mass An elements molar mass in grams per mole is numerically equal to the element s atomic mass in atomic mass units amu Ex mass of copper 63 55 amu Molar mass of copper 63 55g mol 1 mol of copper 63 55g