Density Determination Lab

Jack MurphyAndrew Stetser

20 Sept 2012

Determining the density of various objects was our mission in the

course of this lab. At our disposal were a metric ruler, a graduated

cylinder, an electronic scale, and a Vernier Caliper to assist in the

density calculations. The unknown metal pebbles have a density of

2.63g/cm3 and was concluded to be made of elemental aluminum whose

density is 2.70g/cm3. We had a % error of about 2.59%. The densest

object was the metal cylinder whose density was 7.62g/cm3 and was

most likely made of iron whose density is 7.874g/cm3 and appeared to

be rusting.

The objective of the density determination lab was to resolve the

density of 6 objects given to us. Using different tools available to us, we

needed to discover the mass and volume to determine a density.

The lab is necessary to know how density is an intensive property

and the amount of an object should not affect the outcome of the

density. The method of determining the density of an object is

invaluable because it can be used to conclude what element or

compound it may be. The scientist performing the experiment will be

able to use the skills acquired through this lab in all future labs and

determination of any substance. The results of the densities of each

object should correspond with universally accepted results. The metal

objects are unknown to be either elements or compounds, except for the

metal pebbles; therefore, we cannot determine what the acceptable

results are for those, but the density of the wood can tell us that it is

most likely a piece from a yellow birch tree which has the density of

0.668g/cm3.

Procedure:

Materials:

Vernier Caliper

The following image displays how to

read the Vernier Scale.

The Graduated Cylinder

Used to determine the Volume of irregularly shaped object, the

graduated cylinder allows the user to measure the difference between

the initial volume of water and the final volume to determine the

volume of the object as shown in the following image.

Using water, we can correctly determine the Volume knowing that 1mL

of water = 1cm3. The reading of a graduated cylinder must be read at the

bottom of the meniscus with eye level even with the bottom of the

meniscus.

The Electronic Scale

We used an electronic scale that was set

in the unit of grams and displayed 2 decimal places. The scale must be

set to 0 before weighing the substance. For example, when determining

the mass of the clear fluid, we set the graduated cylinder without the

liquid on the scale and pressed TARE, which will set the scale to 0 with

the graduated cylinder on it. The mass displayed with the liquid will be

the mass of the liquid only.

The 6 objects given were, 1 – a wooden block, 2 – a metal cube, 3 –

a metal slab, 4 – metal cylinder, 5 – metal pebbles, 6 – a clear fluid. Using

the Vernier Caliper, we measured the 3 dimensions of the wooden block

making sure not to repeat the measurement of one side. The length,

width, and height were recorded and multiplied on each other

(length*width*height) to determine the volume. The block was then

placed on the scale after confirming that the scale read 0 without the

block on it. The block was weighed and the mass was recorded. The

mass over the calculated volume (MassVolume) will give us the density of the

object. Refer to the results to see the final recordings. The same

methods were completed for objects 2 and 3. For object #2, we made

sure that the object was a cube by measuring all of the sides.

For object #4, the same process was used but the diameter and

height were recorded. The Diameter needed to be divided by 2 to give

us the radius of the cylinder (r=d2 ). The Volume of a Cylinder is π r2h=V .

Therefore, the volume was determined. The same procedure was used

to determine the density (MassVolume).

The 5th object were multiple metal pebbles of an elemental metal

and we had to conclude which element they were made of. To

determine the mass, they were placed on the scale after the scale was

TARED and read 0. The mass was recorded. Then, we filled the

graduated cylinder to a certain level, enough to completely submerge

the object in question, and recorded as the initial level. The SAME

pebbles were then placed into the graduated cylinder. The cylinder was

then tapped lightly by a pen to dislodge any air bubbles that had

adhered to the pebbles. The level of the water was measured with all of

the same pebbles that were weighed in the graduated cylinder. The level

was recorded as the final volume. The initial volume was subtracted

from the final volume to give us the volume of the pebbles. Knowing that

1mL = 1cm3, we could still get the density in terms of g/cm3. Density

was determined as (MassVolume).

For the clear liquid, the empty, dry graduated cylinder was placed

on the scale and TARED so that the scale read 0 with the cylinder on it.

The liquid was added to the cylinder and was put to an easily

discernable level. The mass read on the scale was of the liquid only as

the graduated cylinder had been TARED out. The mass was recorded,

and the volume was what the liquid filled up to and was recorded.

Density of the liquid was determined by MassVolume .

Results:

WoodenBlock

MetalCube

MetalSlab

MetalCylinder

MetalPebbles

ClearFluid

MASS(grams)

26.44g 5.67g 37.99g 48.15g 1.97g 23.14g

LENGTH(cm)

5.79cm 1.28cm 8.91cm D=1.28cm --- ---

WIDTH(cm)

1.9cm 1.28cm .64cm r=.64cm --- ---

HEIGHT(cm)

3.6cm 1.28 2.55cm 4.91cm --- ---

INITIAL VOLUME

(mL)--- --- --- ---

12mL20mL

FINAL VOLUME

(mL)--- --- --- ---

12.75mL 20mL

VOLUME OF

OBJECT(cm3)

39.6036 cm3

2.0972 cm3

14.542cm3 6.32cm3 .75cm3 20cm3

DENSITY(g/cm3)

.668g/cm3

(.6676)

2.70g/cm3

(2.70367)

2.61g/cm3

(2.6126)7.62g/cm3 2.63g/cm3

(2.626)1.16

g/cm3

(1.157)

Interpretation:

The results from determining the mass and the volume of the wooden

block led to a reasonable density of 0.668 grams per centimeter3. After

exploring the Internet, we found that the wood was most likely made

from a yellow birch tree whose density was precisely 0.668 g/cm3. The

metal cube was in fact a cube and came to a density of 2.70 g/cm3, which

was consistent with the other metal object of similarities during the lab.

For the Metal slab, the mass calculated to be 37.99g, and presented a

volume of 14.541cm3 bringing the density to 2.61g/cm3. We concluded,

however, that the metal cylinder was made of a far more dense metal

than the metal slab, probably Iron (Fe), whose density is 7.874g/cm3, as

it also appeared to be rusting, a familiar characteristic of iron. Its

density calculated to be about 7.62g/cm3. The metal pebbles were very

hard to determine what element they were made of. After several trials

with varying amounts and different pebbles, I determined that they

were pebbles of Aluminum (Al). Their density calculated to be

2.63g/cm3, which is very close to aluminum’s density of 2.70g/cm3. That is

about a 2.59% error. Percent error is calculated by the following

formula (|Your result−Accepted Value|

AcceptedValue×100=%Error ¿. Bubbles may have

adhered to the outside of the pebbles causing a large volume reading

resulting in a lower density reading. This can raise your percent error

determination. Also the pebble may have air bubbles trapped inside

which would not affect the mass, but again would affect the volume.

The clear fluid was an interesting liquid because overtime the liquid

actually became thicker. At the time of my testing, the liquid had a

density of 1.16 g/cm3. For all of these substances, no matter how much

of the substance we had, the density should remain the same because it

is a ratio of mass to volume; therefore, it is an intensive property which

does not rely on how much there is. Mass and volume themselves are

extensive properties because they relate to the amount there is at hand,

but their ratio is intensive because it should not change. Question #2 in

the questions and conclusions states that an unknown metal having a

mass of 13.35g is added to a 50 mL graduated cylinder containing

24.6m: of water. The water level rises to 26.1mL. What is the density of

the object? The density is 13.35 g26.1−24.6

=8.9g /cm3. The density of water is

1.00g/cm3.

This lab performed in class has taught us that being absolutely

precise in determining our answers will lead to consistent results. Many

errors can be very simple and we learned to watch out for those errors

and not to make them again. The mysterious metal pebbles appeared to

be made of elemental aluminum. The densest object we discovered was

the metal cylinder. This lab is absolutely vital in determining unknown

substances, much like the metal pebbles, because almost everything has

a unique density to itself.