Densities Introduction:

Matter has mass and occupies space. For a given homogeneous quantity of matter, the ratio of these properties has a specific value

known as density. Density is the ratio of the mass to the volume:

mass

Density = volume

If the mass is measured in grams and the volume in cubic

centimeters, the density has units of g/cm3 . The table below lists the

densities of some common metals.

Densities of Common Metals

Metal Density in g/cm3 Metal Density in g/cm3

Magnesium 1.74 Iron 7.85

Aluminum 2.70 Nickel 8.60

Zinc 7.04 Copper 8.93

Tin 7.30 Lead 11.34

Experimental: A. Density of a metal cylinder.

Obtain a metal cylinder and record the identification number

stamped in the metal. Determine the mass to 0.001 grams. Next, determine the volume of the cylinder by the following two methods:

(1) Volume by water displacement. Partially fill a 100 mL graduated cylinder and record the volume. Tilt the graduated cylinder

and carefully slide the metal cylinder down into the water. The water in the graduated cylinder must cover the metal cylinder completely. Read and record the new water level. The volume of the metal cylinder is found

by subtracting the initial water level from the final water level.

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(2) Volume by measurement. Measure the height and diameter of the metal cylinder (in cm) using a metric ruler. Calculate the volume (in

cm3) by using the equation: 2 2diameter2

height( )V r h

Using these separate values for the volume (remember that 1 mL = 1 cm3 = 1cc), calculate the density for the metal cylinder. Dont be surprised if the two density calculations are a bit off.

B. Density of a Salt Solution.

By adding various volumes of a salt solution to a 10 mL graduated cylinder and carefully measuring the volume and total weight, a straight-

line graph can be made. The density of the salt solution can be determined from the graph. Plot the weight of the 10 mL graduated cylinder and salt solution on the vertical axis and the volume of the salt solution on the horizontal axis. Draw the best straight line through the points.

The slope of the line is the density of the salt solution. To determine the slope, choose two points on the line some distance apart. Each of these points has two values; one for the x-axis x1, x2; one for the y-axis, y1, y2. The slope is found by the equation:

2 1

2 1

riseslope density

run

y y

x x

Weigh a 10 mL graduated cylinder containing approximately 2 mL,

5 mL, 7 mL, and 10 mL of salt solution. Record the data in a similar manner to the example shown below:

Data

Volume of Salt Solution in mL Weight of graduated cylinder and solution in grams

1.95 32.85

5.16 36.15

7.50 38.52

9.23 41.05

Using your data plot a graph with the weight of the graduated

cylinder and solution on the vertical axis and the volume of solution on the horizontal axis. Mark each point with a bold dot. Draw the best straight line through the points. Clean and dry the graduated cylinder

and record the weight of the empty graduated cylinder from the balance (for comparison).

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Name

Date

Report for Experiment

A. Density of a metal (Show calculations)

Unknown Metal Number

1. Mass g 2. Volume

a. By Volume Displacement

Initial water level ml

Final water level ml Volume ml

b. By measurement

Height cm Diameter cm

Radius cm

Volume cm3

3. Density a. Using Volume by Displacement g/cm3

b. Using Volume by Measurement g/cm3

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B. Density of a salt solution (Show calculations)

1. Salt Solution Number

Volume of Solution in mL

Weight of cylinder

and solution in grams

2. Density from Graph (show calculations below)

g/ml

3. Weight of the Graduated Cylinder from Graph (y-intercept)

g

4. Weight of Graduated Cylinder from Balance g

5. Attach graph to report. Label axes. If you want to use a

graphing software program (e.g., Excel), attach a copy of the

print-out of the graph.

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