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Temperature Scales Boiling point of water Freezing point of water Fahrenheit Celsius Kelvin 212 ˚F 100 ˚C 373 K 180˚F 100˚C 32 ˚F 0 ˚C 100 K 273 K Notice that 1 Kelvin degree = 1 degree Celsius Calculations Using Temperature • Generally, temperature is used in K (kelvin) for chemistry • T (K) = t (˚C) + 273.15 • Body temp = 37 ˚C + 273 = 310 K • Liquid nitrogen = -196 ˚C + 273 = 77 K DENSITY - an important and useful physical property Density = Mercury mass (g) volume (cm 3 ) Platinum Aluminum 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3 1 Relative Densities of the Elements 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. 2. Calculate volume in cubic centimeters. 3. Calculate the density. 2 SOLUTION 1. Get dimensions in common units. 0.95 mm • 1cm = 0.095 cm 10 mm 2. Calculate volume in cubic centimeters. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3 Note only 2 significant figures in the answer! 3. Calculate the density. 57.54 g 6.4 cm 3 = 9.0 g / cm 3 PROBLEM 2: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? Solve the problem using DIMENSIONAL ANALYSIS. PROBLEM 2: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? First, note that 1 cm3 = 1 mL Strategy 1. Solve density equation for mass… mass = density x volume 2. Use density to calculate mass (g) from volume (mL). 3. Convert mass (g) to mass (lb)Need to know conversion factor 454 g = 1 lb 3 Convert volume to mass 95 cm3 • 13.6 g cm3 = 1.3 x 10 3 g Then convert mass (g) to mass (lb) 1.3 x 10 3 g • 1 lb = 2.8 lb 454 g 4