bad

DensityandBuoyancyVirtualLab.docx

http://web.mst.edu/~gbert/balance/ABal.html

Instructions

Specific Gravity of a Solid: The specific gravity (SG) of a material is the ratio of its density to that of water at the same temperature and pressure. The difference between the weight of a solid in air and under water is equal to the weight of water displaced by the volume of the sample:

SG = (weight in air)/(weight in air - weight under water) Eq 1

These values are normally reported to only three significant digits.

1. Select water as the liquid and select a solid sample. 2. Tare the balance. 3. Select sample position as weigh in air and record the value. 4. Select sample position as weigh under liquid and record the value. 5. Repeat steps 2-4 at least twice and calculate values for SG with Eq 1. 6. Average your results and estimate the uncertainty of this value.

Volume of a Solid and Density of a Solid:

All fluids, including air, exert a buoyancy effect. The weight of a solid immersed in a fluid (WF) is related to the weight in vacuum (WVac) by the volume (V) of the sample and the density of the fluid (DF):

WF= WVac- VDF .

The volume may be determined by weighing the solid in two fluids of known density , such as water (WW, DW) and air (WA, DA):

V = (WA-WW)/(DW - DA) Eq 2.

Values for the density of water at various temperatures are provided by the link density of water. The density of air may be estimated at temperature (t, oC) and 1 atm pressure: DA = 0.353/(t + 273.15) .

1. Select water as the liquid and select glass as the solid sample. 2. Tare the balance. 3. Select sample position as weigh in air and record the value. 4. Select sample position as weigh under liquid and record the value. 5. Repeat steps 2-4 at least twice and calculate values for V to four significant digits with Eq 2. 6. Average your results and estimate the uncertainty of this value.

The density of the glass sample can be calculated by correcting the weight in air to the weight in vacuum and dividing by the volume:

Dsample = (WVac/V) = (WA/V) + DA Eq 3.

The densities of other solids may be determined to about ± 0.1% by this method.

Density of a Liquid: After determining the volume (V) of the glass sample (or any other solid), the densities of other liquids (DL) may be determined by the difference between the weight of the glass sample in air (WA, DA) and when immersed in the liquid (WL):

DL = DA + (WA - WL)/V Eq 4.

1. Select a liquid and select glass as the solid sample. 2. Tare the balance. 3. Select sample position as weigh in air and record the value. 4. Select sample position as weigh under liquid and record the value. 5. Repeat steps 2-4 at least twice and calculate values for DL to four significant digits with Eq 4. 6. Average your results and estimate the uncertainty of this value.

Density of Water

Temperature C Density (g/ml)

10 0.99973

20 0.99823

30 0.99567

40 0.99224

50 0.98807

DATA SHEET #1: SPECIFIC GRAVITY OF SOLIDS temp oC ______

Sample Material: _________________	Sample #1	Sample #2	Sample #3	Sample #4
A Weight in Air (Wair,g)	_____________	_____________	_____________	_____________
B Weight in Water (g)	_____________	_____________	_____________	_____________
C Buoyancy Effect (g) [A-B]	_____________	_____________	_____________	_____________
D Specific Gravity [A/C]	_____________	_____________	_____________	_____________
	Average: SG = ______________ ± ____________

Sample Material: _________________	Sample #1	Sample #2	Sample #3	Sample #4
A Weight in Air (Wair,g)	_____________	_____________	_____________	_____________
B Weight in Water (g)	_____________	_____________	_____________	_____________
C Buoyancy Effect (g) [A-B]	_____________	_____________	_____________	_____________
D Specific Gravity [A/C]	_____________	_____________	_____________	_____________
	Average: SG = ______________ ± ____________

Sample Material: _________________	Sample #1	Sample #2	Sample #3	Sample #4
A Weight in Air (Wair,g)	_____________	_____________	_____________	_____________
B Weight in Water (g)	_____________	_____________	_____________	_____________
C Buoyancy Effect (g) [A-B]	_____________	_____________	_____________	_____________
D Specific Gravity [A/C]	_____________	_____________	_____________	_____________
	Average: SG = ______________ ± ____________


Unknown: Code # _______________	Sample #1	Sample #2	Sample #3	Sample #4
A Weight in Air (Wair,g)	_____________	_____________	_____________	_____________
B Weight in Water (g)	_____________	_____________	_____________	_____________
C Buoyancy Effect (g) [A-B]	_____________	_____________	_____________	_____________
D Specific Gravity [A/C]	_____________	_____________	_____________	_____________
	Average: SG = ______________ ± ____________

DATA SHEET #2: DENSITY OF LIQUIDS temp oC ______

Dair = 0.353/(273 + t) = ______________g/cm3 Dwater = ______________ g/cm3

Volume: V = (Wair - Wwater)/(Dwater - Dair) ; Dwater - Dair = _______________ g/cm

Determination of the Volume of the Glass Sample:

A Weight in Air (Wair,g)	________________	________________	________________
B Weight in Water (Wwater,g)	________________	________________	________________
C Buoyancy Effect (g) [A-B]	________________	________________	________________
D Volume (cm3)	________________	________________	________________
Average Volume:	V = ______________ ± ____________ cm3

Density of a Liquid: Dliquid = Dair + (Wair - Wliquid)/V

Known Liquid: ______________________________
A Weight in Air (Wair,g)	________________	________________	________________
B Weight in Water (Wwater,g)	________________	________________	________________
C Buoyancy Effect (g) [A-B]	________________	________________	________________
D Density (g/cm3) [C/V + Dair]	________________	________________	________________
Average Density:	D = ______________ ± ____________ g/cm3

Known Liquid: ______________________________
A Weight in Air (Wair,g)	________________	________________	________________
B Weight in Water (Wwater,g)	________________	________________	________________
C Buoyancy Effect (g) [A-B]	________________	________________	________________
D Density (g/cm3) [C/V + Dair]	________________	________________	________________
Average Density:	D = ______________ ± ____________ g/cm3

Unknown Liquid:Code #______________________
A Weight in Air (Wair,g)	________________	________________	________________
B Weight in Water (Wwater,g)	________________	________________	________________
C Buoyancy Effect (g) [A-B]	________________	________________	________________
D Density (g/cm3) [C/V + Dair]	________________	________________	________________
Average Density:	D = ______________ ± ____________ g/cm3