Spring 2008 Name__________________

Physical Science Experiment

Density

Object - To measure the density of solids, liquids, and gases.

The material on this lab has not yet been covered in class. You will need to read section 4.4 before completing this page. You will also need to read this lab, especially the second page that has the formulas needed to calculate the volume.

In this lab, you will use the density of objects to attempt to determine the material of which they are composed.

Variations in density are responsible for many of the effects with weather and geological processes, such as winds, precipitation, lava flows and volcanic eruptions.

Theory

The density of a substance is defined as the mass of an object divided by its volume.

For example if 70 grams of a metal occupy 10 cm3, its density is given by:

d = M/V = 70 grams/103cm3 = 7 g/cm3

You must complete these first six questions before arriving in lab or you will lose points from your lab score.

NOTE: Formulas for volume are on the next page!

1. What is density and how will you calculate it? (Write the equation for density and explain it in words.)

2. If a cylinder has a radius of 2 cm, a length of 4 cm and a mass of 600 grams, calculate the volume and density? Show all the steps in your work. Density may be expressed in the units of g/cm³.

volume =

density =

3. Calculate the volume of a sphere of radius 3 cm. (Show your work.)

4. Calculate the volume of a cube with 7 cm on a side! (Show your work.)

5. Read the entire lab then describe in your own words how you will measure the density of air.

DENSITY TABLE

Substance g/cm3 Substance g/cm3

Solids

Aluminum 2.7 Brass 8.4

Copper 8.9 Glass Crown 2.5-2.7

Glass Flint 3.0-3.6 Gold 19.3

Iron and steel (general) 7.88 Lead 11.3

Nickel 8.8 Silver 10.5

Wood Oak 0.60-0.90 Wood Pine 0.35-0.50

Zinc 7.1

Liquids

Alcohol Ethyl 0.79 Alcohol Methyl 0.81

Carbon tetrachloride 1.60 Gasoline 0.68-0.75

Glycerine 1.26 Mercury 13.6

Turpentine 0.87 Water 1.00

Gases(at STP)

Air 0.001293 Carbon dioxide 0.001975

Helium 0.000179 Hydrogen 0.000089

Nitrogen 0.000125 Oxygen 0.00143

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To calculate density, two separate measurements are necessary, a measurement of the mass of the object and measurement of its volume.

The first part of the experiment is to be done individually, but you are free (an encouraged) to help one another. Parts 10 – 14 may be done as a group.

Parallelepiped (box) V = length x width x height;

(cylinder) V = πr2h;

(sphere) V = (4/3)πr3.

Determine its mass on a balance, then use equation (1) to determine the density, (always give your answers in grams/cm3). The chart at the top of this page is to be used to give an estimate of the substance from which the object is made. To maximize efficient use of the equipment, your instructor will ask certain groups to begin at different places on the lab sheets. Use the vernier calipers whenever possible.

The five solid objects are to be dome individually, not with the others of your group. Each person should do at least one sphere, one cylinder and one parallelepiped. Do not use the same objects as any other person in your group!

5) a) write a description of the object including its shape, color, and other characteristics =

b) Dimensions (give the results of your measurements) =

c) Volume =

d) Mass =

e) Density = _______________/ ___________________ =

f) best guess as to material from which object is made =

6) a) write a description of the object including its shape, color, and other characteristics =

b) Dimensions (give the results of your measurements) =

c) Volume =

d) Mass =

e) Density = _______________/ ___________________ =

f) best guess as to material from which object is made =

7) a) write a description of the object including its shape, color, and other characteristics =

b) Dimensions (give the results of your measurements) =

c) Volume =

d) Mass =

e) Density = _______________/ ___________________ =

f) best guess as to material from which object is made =

8) a) write a description of the object including its shape, color, and other characteristics =

b) Dimensions (give the results of your measurements) =

c) Volume =

d) Mass =

e) Density = _______________/ ___________________ =

f) best guess as to material from which object is made =

9) a) write a description of the object including its shape, color, and other characteristics =

b) Dimensions (give the results of your measurements) =

c) Volume =

d) Mass =

e) Density = _______________/ ___________________ =

f) best guess as to material from which object is made =

10) To determine the density of water, weigh the dry 100 cm flask and record its mass. (The three flasks have been carefully selected to have the same empty weight.) Then weigh the flask with water.

The volume of the liquid in the flask is 100 cm3

a) mass of cylinder plus 100 cm3 of water = _________________

b) empty cylinder mass = _________________

mass of liquid = ___________________

(a-b)

density of liquid = _______/_________ =

(Show work)

11) To determine the density of the salt solution, weigh the dry 100 cm flask and record its mass (The three flasks have been carefully selected to have the same empty weight.) Then weigh the flask with the salt solution.

a) mass of cylinder plus 100 cm3 of salt water =_________________

b) empty cylinder mass = _________________

mass of liquid = ___________________

(a-b)

density of liquid = _______/_________ =

(Show work)

12) Go to the front of the room and use the hydrometer to obtain the densities of the water and the salt solutions. (If you do not remember how to use this instrument, ask your instructor for assistance.)

a)Density of Water = ___________

b)Density of Salt Water = ________________

13) Calculate the percentage differences between these readings and those of items 10 and 12. Compare the tap water with the tap water and the salt water with the salt water. The calculation of the percent difference is to take the difference between the two readings and divide by the answer considered to be the most reliable. (In your case divide by the result given by the hydrometer.) Be sure to show your work!

% difference for tap water = result from 10 - result from 12a

result from 12a

% difference for tap water =

% difference for salt water = result from 11 - result from 12b

result from 12b

% difference for salt water =

14) Density of air

a) Place the metal ball on the left side of the balance and determine its mass (with the valve open). Record the position of the slide at the top of the balance. This is the only reading you will need to record as total weight of the ball is not important, only the change in weight as the air is pumped out of the ball.

First reading (full of air) mass = ____________________ g

b) Using the vacuum pump, remove all the air from the sphere which has the nozzle and valve. The instructor will show how to use the sound of the pump as an indicator to know when all the air has been removed.

c) After the pump has run for about 2 minutes, close the valve and quickly move the slide to obtain an approximate reading. It is not necessary to record this weight.

d) Due to the fact that there is a small leak in the metal ball you now need to pump the air from the ball one more time and once again quickly weigh it

e) Ball without air = __________________ g

f) mass of air = _________________ g

g) Measure the circumference of the sphere with the string and use the formula for circumference (= 2πr) to determine the radius.

circumference = ______________ radius = _____________

volume = ______________ = _____________________

h) density of air = m/V = ___________/__________ = ______________

density of air from table (see page 2) = _______________

percent error = __________________________

(See item 13 for equation)

(Due to the small weights involve and the precision of the balance used, a 100% error is acceptable on this part of the experiment, on the other parts, the error should be 5% or less)

15) Tell in your own words what density is.

Did you think this was a good experiment? Explain how you think it could be improved.