Dr. Fred Omega Garces

Transcription

1 2.05 Density and Specific Gravity Mass Volume relationship Dr. Fred Omega Garces Chemistry 100, Miramar College Density and Specific Gravity

2 Eureka!!!! King Hieron wanted a new crown and so he gave the goldsmith some gold and told him to use all the gold to make a new crown. When he got his crown back it felt light. He thought that the goldsmith had cheated him and wanted Archimedes to find out if he had been duped. Archimedes did not know how to verify the authenticity of the crown initially, but he did know that if he could the density of the crown he could compare it to gold. One day, while taking a bath he got into the tub and some of the water went over the sides of the tub. He then thought of the crown. He got out of the tub and ran to the king s palace, all naked, yelling Eureka, Eureka ( I found it, I found it). And so is the famous story of Archimedes the streaker! Archimedes Density and Specific Gravity

3 Density (& Specific Gravity) Physical property An observable (or measurable) property of matter i.e., color, boiling pt, melting pt, conductivity, texture, specific heat and density. Consider what occurs when vinegar and oil is mixed. The oil floats on top and the vinegar and the herbs are at the bottom. We say that the oil is less dense than the vinegar Density and Specific Gravity

4 Density : definition Density (d or r) define as: mass per unit volume. Density relates the mass to the volume for a given substance Density and Specific Gravity

5 Density of certain Substances Consider the following densities (physical property) for different substances. Metal Symbol density (g/cc) gold Au 19.3 mercury Hg lead Pb water H 2 O 1.00 ethanol C 2 H 5 OH Density and Specific Gravity

6 Density (translator) is a conversion factor We can redefine the density as a conversion factor between mass and 20 C gold ml sugar ml H 2 O ml Olive oil ml C 2 H 5 OH ml Example: L of ethanol will have what 20 C? Mass = L * 1000mL 1.0L * g 1.0mL = 39,450 g Density and Specific Gravity

7 Density calculation: Example 2 : If a metal object (32.0 g ) is claimed to be gold, how can this be verified? (check density) Mass of solid = g Volume (initial) Volume (final) = ml = ml Density and Specific Gravity

8 Density calculation: Example 2 : If a metal object (32.0 g ) is claimed to be gold, how can this be verified? (check density) Mass of solid = g Volume (initial) Volume (final) = ml = ml Volume Solid= V f - V i = ( ) ml Mass Density of solid = Volume = g 1.66 ml = 19.3 g ml Density and Specific Gravity

9 Density calculation: Example 3 : What is the mass of 1.00 gallon of gold? In class assignment Density and Specific Gravity

10 Density calculation: Example 3 : What is the mass of 1.00 gallon of gold? Conversion factors: 1.00 gal = L g = 1.00 lb 1.00 gal Au L 1 gal 1000 ml 1 L 19.3 g 1 ml 1.0 lb g = lb = 161 lb Density and Specific Gravity

11 Specific Gravity The ratio between the density of the sample over the density of water ( at 20 C). A unitless quantity s.g. = d (sample) d C) g cc g cc " $ # % $ unitless S.g. is an indicator of how much more dense a substance is relative to water. s.g. > 1 (more dense than H 2 O ) Sinks in water s.g. < 1 (less dense than H 2 O ) Floats in water Density and Specific Gravity

12 Specific Gravity and Density In this class, we will treat Density ~ specific gravity unless otherwise stated a) A hydrometer shown measures a specific gravity over a range of to Use of hydrometers include the measurement of the specific gravity -and thus the acid content of battery acid in your car, the amount of alcohol in wine, The relative densities of some liquids. Immiscible liquids will separate into layers, with the most dense liquid going to the bottom and the least dense liquid rising to the top. the sugar content of maple syrup and the dissolved solids in urine. B) A pycnometer is shown to hold 10 ml Density and Specific Gravity

13 Intensive vs Extensive Some properties of matter are quantity dependent i.e., 50 g, 50 L If property is amount dependent call this Extensive property. Others are quantity independent i.e., bpt H 2 O = 100, density (H 2 O) = 1.00 g/cc If property is amount independent call this Intensive property Density and Specific Gravity

14 Summary on Density Density (Specific Gravity) is a conversion factor between mass and volume. Density is an intensive property (it is amount independent) Density and Specific Gravity