density-07.html

Chem 120 / Dr. Rusay

Density & Specific Gravity

Flat-topped iceberg in the Ross Sea region of the Antarctic.
Photograph: J. Anderson, Rice University.

Web references, reading and links:

Applications of Density

Determining the density of an unknown liquid
Identifying an unknown metal from its specific gravity/density
Using density to estimate the mass of an iceberg
Determining the alcohol content of beer from density

Chemistry 120 Experiments, Dr. Rusay, Density of Liquids and Solids

II) Using the data for the unknown metal cylinder that you generated in Experiment 1, calculate its density and identify the metal from the specific gravities listed in the above Web references. List more than one possibility if you cannot be conclusive.

III) Using density to estimate the mass of an iceberg:

The Above image shows three spheres of different sizes floating in pure water. Like these spheres ice floats in water.

When an object is put into a liquid, if the object displaces less liquid than its total volume, the object will float and have a positive bouyancy. If the object weighs more than the weight of the liquid displaced by the object's total volume, the object sinks or has a negative bouyancy. When these principles were discovered in the 3rd century B.C. by Archimedes, he reportedly exclaimed "EUREKA"! http://en.wikipedia.org/wiki/Buoyancy

These relationships can also be related to the relative densities of the liquid and the object, that is, their respective ratios of mass to volume (densities). Water has a density of 1.00 g/cm³. Its density is at a maximum at 4^oC and density decreases with temperature. If an object has a density less < 1.00 g/cm³, it will float in pure water. If it is > 1.00 g/cm³, it will sink. Ice has a density of 0.91-0.92 g/cm³and floats. In the floating spheres, the volume of the portion of the sphere below the surface multiplied by the density of the liquid (water in this case) equals the total mass of the object. Submarines use this principle to submerge and to surface by varying the relative density of the submarine using air and ballast. To learn more about submarines see: http://www.onr.navy.mil/focus/blowballast/sub/work2.htm and see an emergency surfacing illustrating controlled buoyancy in the extreme http://www.nisk.k12.ny.us/departments/msla/Iroq/NavyPr/submarine%20resources/emerblow.avi.This relationship is also the basis for the workings of a hygrometer, an instrument used to measure the specific gravity (density) of liquids. Hygrometers are commonly found in auto repair shops where they are used to test batteries by measuring the level of a float that is placed into a battery's electrolyte solution. A scale is read that provides the density of the solution which translates to its ability to conduct electricity.

Tables of Physical Data
Object	Diameter or length	Mass	Object's Volume	Object's Density	% Volume of Object below the surface
Sphere 1	10.0 mm	0.4975 g
Sphere 2	22.0 mm	4.7655 g
Sphere 3	37.0 mm	0.9763 g
Cube	10.0 mm	1.0160 g

Knowing the density of the sea water and making a few assumptions and approximations, it is possible to estimate how much of the iceberg is below the surface and the iceberg's total mass. The iceberg in the photo will be used for the approximations. It likely broke off of the Antarctic ice shelf. Icebergs such as this one have been reported to be up to 100 km long, 30-40 km wide, 90 m high and 800 m thick.

B) The above iceberg in the Ross Sea of Antarctica is approximately the size of the State of Rhode Island. Sea Ice can have densities of 0.857 to 0.92 g/cm³. Asmall portion of the iceberg broke off, which is in the photo at teh tp of the page. The density of this smaller iceberg is 0.890 g/cm³and the density of the upper layer of water in the Ross Sea is 0.999 g/cm³. The shape of the iceberg above water can be approximated as a rectangular block. The surface volume can be calculated from the estimated dimensions :

Length = 500 meters, Height = 90 meters, Width = 150 meters.

2) Calculate the total mass of the iceberg.

(Clearly show your answers and calculations. Remember, the percent difference in the densities will equal the percent of the volume of the iceberg under water since the mass of sea water displaced by the volume of the iceberg beneath the surface is equal to the total mass of the iceberg.)

Extra credit: Write a sentence or two describing how the density and icebergs in the Arctic Ocean relate to global warming and the fate of polar bears.

IV)

http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry7.html

http://leebrewery.com/beermath.htm

(1) What is the percent alcohol by mass? (2) What is the percent alcohol by volume? (3) What is the number of calories per pint of a homemade beer which had an original specific gravity of 1.10 and a final specific gravity of 1.05?

Learn more about the history and chemistry of beer:
See microscopic views of different beers from all over the world:
http://micro.magnet.fsu.edu/beershots/index.html