Understanding Density and Matter Measurement

AP ChemistryPreface and Chapter 1 Matter and Measurement Mrs. Hallman 9/2013

Density • Definition: Mass per unit volume of a substance • Formula: D = m/V ; units: g/mL, g/cm3, kg/L

Sample Problem • Sample Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3). • Strategy • 1. Get dimensions in common units. m = 57.54 g L = 9.36 cm W = 7.23 cm Thickness (Height) = 0.95 mm = 0.095 cm • 2. Calculate volume in cubic centimeters. V = LxWxH = (9.36 cm)(7.23 cm)(0.095 cm) = • 3. Calculate the density. D = m/V Be sure to check sig figs

Density as a conversion factor Sample Problem: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? • First, note that 1 cm3 = 1 mL • Strategy 1. Use density as a conversion factor to calculate mass (g) from volume. 2. Convert mass (g) to mass (lb) Need to know conversion factor; 454 g = 1 lb

A last thought on density • Density of water changes with temperature – why?

Extensive & Intensive Properties • Intensive property - is a physical property of matter that does not depend on the system size or the amount of material in the system • Examples: density, color hardness, melting point, boiling point • Extensive property – any property that depends on the size of the system. A property that changes as the amount of matter changes. • Examples: mass, volume, temperature, energy released/absorbed

Temperature Discussion

Classification of Matter • State of matter: gas, liquid, solid • Kinetic Molecular Theory: A theory of the behavior of matter at the molecular level • Kinetic Energy: The energy of a moving object, dependent on its mass and velocity • K.E. = 1/2mv2

Solid - Liquid - Gas

Matter at the Macroscopic and Particulate Levels • Matter has both • Macroscopic –measurable and observable to the naked eye • Macroscopic properties - color, length • Submicroscopic or particulate –not measurable with a microscope • Particle size, chemical bond length

Matter Q’s • 3 examples • 2 forms of energy • Is energy a form of matter • Symbolic level

Units of Measurement • Measurement System – in summer work • Length base unit – meter • Conversions: 2.54 cm = 1 inch • Mass base unit – kilogram • Conversions: 453.5 g = 1 pound (only on earth!) • Time base unit – second • Conversions: 1 hour = 60 minutes; • 1 minute= 60 seconds (NOTE THESE ARE EXACT NUMBERS)

Derived units • We did this - you tell me! • Volume –

Dimensional Analysis -1 • A problem solving method – • Example: how many seconds in a day ?? • 1 day 24 hours 60 min 60 sec = 1 day 1 hour 1 min

Dimensional Analysis-2 • Find the surface area of a room 20 feet by 12 feet in square meters. ( Use 2.54 cm = 1 inch)

Dimensional Analysis -3 • Using density as a conversion – What is the mass of a gold cube with 2 inch sides? (density of gold =19.3 g/cm3) • Hint: need volume in cubic centimeters -

Accuracy vs. Precision • Accurate – close to the true value • Precision – reproducibility of the measurement • Percent Error:

Problem Solving • State the problem • Organize the information • Determine what you know & what you need to know • Determine the strategy • May stem from prior knowledge • Write down each step • NO WORK NO CREDIT!! • Check your answer • Is it reasonable????

HOMEWORK ASSIGNMENTS • Chapter 1 • Density p. 39 # 21, 23, 25, 55, 57 • Unit Conversions p. 40 31, 33, 35, 37, 53, 59 • Problem solving p. 40 45, 47, 49, 61, 63, 77 • Dimensional Analysis Worksheets • Sig fig review worksheet

Understanding Density and Matter Measurement