DENSITY

MEASUREMENT OF PHYSICAL PROPERTIES: DENSITY

Introduction

According to the definition Density is the physical property that allows us to compare the mass of substances for a specific volume. In this Lab activity that took place in Deree College, Agia Paraskevi Campus we deal with the density of solids and density of liquids. The main purpose of this experiment is to understand what in reality density means, how we can measure it, how useful it is, what is the difference between density of solids and liquids, if the measurements that we did are been accurate and how we can calculate the percentage errors.

materials

3 different metals
A) copper
B) iron
C) aluminum
- 3 Different liquids A) Water B) Olive oil C) Alcohol
- Balance
- Cylinders of 25ml, 100ml
- Calculator

DATA/RESULTS
In this Lab activity we saw the differences between the density of solids and the density of liquids.
Firstly we obtained three different solids a piece of aluminum, a piece of copper and a piece of iron, and we measured their masses by using the balance. Also, we measured their volume by using a cylinder with distilled water, then we have measured the volume, and then we put in the metal and recorded the total volumes. After that we calculated each density and we recorded the average density (by classmates). Also, I found the literature density through a web search. Finally we calculated the percentage error by using the following formula: (Density from data – Density from literature) / Density from literature * 100
The results are shown in the following table:
DATA
ALUMINUM
COPPER
IRON
MASS OF SOLID
47.5
160
143.5
VOLUME OF WATER
79
77
76
VOLUME OF WATER WITH SOLID
97
96
95
VOLUME OF SOLID
18
19
19
DENSITY FROM DATA
2.6388
8.4210
7.5526
AVERAGE DENSITY
2.56
8.39
7.21
DENSITY FROM LITERATURE
2.7
8.92
7.87
PERCENTAGE ERROR
(2.63388-2.7) / 2.7 *100 =
-2.26%
(8.4210-8.92) / 8.92 *100 =
-5.59%
(7.5526-7.87) / 7.87 *100 =
-4.27%
Secondly we did the same experiment with liquids. We obtained a cylinder of 25 ml and we measure it’s mass by using the balance. Then we placed 15-25 ml of each liquid and we recorded its volume. Then, we measured the mass of the cylinder with the liquid on it and we calculated the mass of liquid by deducting from the total mass the mass of cylinder that we had previously measured. After we did this for the three liquids that we had (water, olive oil, alcohol) we found each density, average density and the percentage error. Also, through internet search the literature density.
The results are shown in the following table:

DATA
ALCOHOL
WATER
OIL
MASS OF CYLINDER
60.4
60.4
60.4
MASS OF CYLINDER AND LIQUID
76.5
80.8
75.4
MASS LIQUID
16.1
20.4
15
VOLUME OF LIQUID
20
20
16.9
DENSITY FROM DATA
0.805
1.02
0.88
AVERAGE DENSITY
0.79
1.0
0.80
DENSITY FROM LITERATURE
0.788
1.0
0.80-0.92
PERCENTAGE ERROR
(0.805-0.788) /
0.788 * 100=
2.15%
(1.02-1) / 1*100=
2%
(0.88-0.80) / 0.80*100=
9.09%
Finally we created mixtures among liquids. We obtained three 100 ml beakers and we placed:
a) 10ml of distilled water and 10ml of olive oil
b) 10ml of distilled water and 10ml of ethanol
c) 10ml of olive oil and 10 ml of ethanol
The results are the following:

DATA
OBSERVATION
WATER AND OIL
HETEROGENEOUS MIXTURE
WATER AND ALCOHOL
HOMOGENOUS MIXTURE
ALCOHOL AND OIL
HOMOGENOUS MIXTURE

Discussion

According to the experiment we concluded that among the three metals, the copper had the higher density (8.4210 g/ml) and the aluminum the lower (2.6388g/ml) where the iron’s density was 7.5526 g/ml. Since the density is the mass over the volume (d=m/V) we can say that the metal with the higher mass it has also the higher density, something that verifies our results that shown the copper with the higher mass to has the higher density. On the other hand if the mass of a solid is low and its volume is high then, from the formula, we see that the density will be low, as we observed with aluminum which had the lower mass and the biggest volume and also the lowest density.

The purity of our samples depends of if the density that we measured is closed to the density given by literature. From the result table we see that the closest is the aluminum which has only 0.06 g/cm3 difference from pure aluminum and it seems the most pure. The copper has 0.5 g/cm3 where the iron has 0.29 g/cm3 difference in density. Density is a very helpful tool in order to measure the purity of a precious metal like gold. As close the density of a gold item is to the density of pure gold, such pure is this gold item.
If we compare the densities of the liquids we see that the water with the higher mass it has also the higher density. If now compare the densities of the solids and liquids we conclude that the liquids have by far less density than solids
Density can explain why ice floats on water. This happens because when the molecules of water cold to become ice, they expand in volume, the mass stays constant and the volume increases so, the density decreases according to the formula.
According to the percentage errors we conclude that copper and iron had a high percentage error above 3% which means that something went wrong in the laboratory process. That’s why the densitometers are very useful because error can occur easily and the laboratory equipment is not enough for exact measurements.

conclusion

After this Lab activity we approach the density from many different ways and now the calculation of densities of solids and liquids is easy stuff. Also, we understand how important density is and without the appropriate equipment the percentage errors can be very high. Finally, we see how density can give us explanations for daily wired things that happen and never had we though about them, such as why the ice floats on water.