# Density: a characteristic Property Fides Ybanez Abstract

 Date 15.05.2016 Size 48.51 Kb. #48567               Density: A Characteristic Property
Fides Ybanez
Abstract
The objective of this experiment was to know how to determine density and understand that density characterizes specific substances. Mass, for both liquid and solid, was measured using an electronic analytical balance while the volume for liquid used a volumetric pipette. Since the solids were irregularly-shaped, water displacement method of measuring its volume was used.
The experiment was divided into two parts. The first part was determining the densities of liquids such as acetone, ethyl alcohol, ethyl acetate and water. The density of an unknown substance was also determined by measuring its mass and volume. The results showed a density of 0.899 ± 0.01 g/mL which is characteristic of ethyl acetate.
The second part determined the densities of tin and silicon. From these densities, the density of germanium was calculated at 72.53 ± 0.02 g/mL.

Introduction
Density is a physical property and is one of the different ways to identify substance because each substance has unique density. (http://www.elmhurst.edu/~chm/vchembook/120Adensity.html) Density is an intensive property which means it is a property that is independent of the amount of matter.
Density is the ratio between mass and volume. It tells whether a substance is compact or loosely packed. Mathematically, density is mass divided by its volume:

m

D =

V

Where:

D is the density;

M is the mass; and

V is its volume.
Density is commonly compared to water and used to know whether a substance will float or sink when placed in it. Water has a density of 0.9999 g/mL at 1 atm and 4oC. Anything that is less dense than water will float and those that are more dense will sink.
Densities of substances used in this experiment are listed in the table below.
Table 1-1. Densities of Some Liquid Substances at 25oC.
 Liquid Substance Density (g/mL) Acetone, CH3COCH3 0.791 Ethyl Acetate, CH3COOCH2CH3 0.902 Ethyl Alcohol, CH2CH3OH 0.785 Hexane, C6H14 0.659 Silicon, Si 2.33 Tin, Sn 7.31 Germanium, Ge 5.323

Since density is a way of identifying substances, it will tell the identity of the unknown substance. If the density obtained will be close to any of those listed in Table 1-1, then the identity of the substance will be known.

Experimental Methods
Measurement of the mass was done using an electronic analytical balance with an accuracy of 0.0001 and volume measurements were done using 1-mL volumetric pipettes and pipettors.
A previously cleaned and dried empty vial with stopper was weighed in the balance. Using a 1.00-mL volumetric pipet, a liquid samples was pipetted and placed in the weighed vial. This was repeated for all liquid samples and for each liquid sample, three trials were prepared and measured. The same procedure was done for the unknown liquid sample. All data are recorded in Table 1-2.

For the density of solids, an empty 25-mL beaker was weighed. Enough amount of solids were placed in the beaker and weighed. A 10-mL graduated cylinder was half-filled with water and the solid was placed in it. The amount of solid placed was enough to make the water rise to about 3 mL. The same procedure was done for both solids used and three trials for each solid were done. Data for this part of the experiment are recorded in Table 1-3.

The density of germanium was obtained from the densities of tin and silicon.

Results
Part A of the experiment is the determination of densities of different liquid substances. The mass and volume obtained from this experiment and the calculated densities of the liquid substances are shown in the table below.
Table 1-2. Mass, Volume & Densities of Liquid Substances.
 Liquid Substance Acetone Ethyl Acetate Hexane Trial Number 1 2 3 1 2 3 1 2 3 Mass of Empty Vial + Stopper (grams) 64.9774 64.9774 64.9774 69.9967 69.9967 69.9967 68.2992 68.2992 68.2992 Mass of Vial with Liquid and Stopper (grams) 65.7822 65.8510 65.7882 70.9762 70.9318 70.9816 69.0499 69.0812 69.0772 Mass of Liquid (grams) 0.8048 0.8736 0.8108 0.9795 0.9351 0.9849 0.7507 0.7820 0.7780 Volume of Liquid (mL) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Density of Liquid (g/mL) 0.805 0.874 0.811 0.980 0.935 0.985 0.751 0.782 0.778 Mean (g/mL) 0.830 0.967 0.770 Accepted Density (g/mL) 0.791 0.902 0.659

Density was calculated using the formula D=m/V. A sample calculation of the density of acetone using trial 1 is shown below.

m mass of acetone 0.8048 g

D = = = = 0.805 g/mL

V Volume of acetone 1.00 mL
A sample calculation of how the mean density for acetone was obtained is also shown below.
Trial 1 Density + Trial 1 Density + Trial 1 Density

Mean Density of Acetone =

3

0.8048 + 0.8736 + 0.8108

= = 0.830 g/mL

3
From the table above, average densities for acetone, ethyl acetate and hexane are 0.830 g/mL, 0.967 g/mL and 0.770 g/mL, respectively.

Calculated absolute deviation (based on accepted densities in Table 1-1) and percent error on densities of liquid substances are shown in Table 1-3 below.
Table 1-3. Deviation and Percent Error on Densities of Liquid Substances.
 Liquid Substance Acetone Ethyl Acetate Hexane Trial Number 1 2 3 1 2 3 1 2 3 Density of Liquid (g/mL) 0.805 0.874 0.811 0.980 0.935 0.985 0.751 0.782 0.778 Accepted Density of Liquid (g/mL) 0.791 0.902 0.659 Absolute Deviation 0.014 0.083 0.020 0.078 0.033 0.083 0.092 0.123 0.119 Average Deviation 0.039 0.065 0.11 Density (g/mL) 0.830 ± 0.039 0.967 ± 0.065 0.770 ± 0.11 Error (%) 4.9 7.2 16

Calculation for the percent error for acetone is shown below. It uses the formula:

⃒ Accepted Value – Experimental Value ⃒

Percent Error = -------------------------------------------------- x 100

Accepted Value
⃒ 0.791 - 0.830 ⃒

= ------------------------- x 100 = 4.9 %

0.791
The table above shows the experimental values of the densities of the liquid samples obtained are 0.830 ± 0.039 g/mL for acetone, 0.967 ± 0.065 g/mL for ethyl acetate and 0.770 ± 0.11 g/mL for hexane. Furthermore, the errors from the experiment were 4.9% for acetone, 7.2% for ethyl acetate and 16% for hexane.

Table 1-4 shows the details obtained or the unknown liquid.

Table 1-4. Determination of Density of Unknown Liquid.
 Trial 1 Trial 2 Trial 3 Mass of Empty Test Tube + Stopper (grams) 45.1035 45.1035 45.1035 Mass of Test Tube with Unknown Liquid and Stopper (grams) 46.0395 45.9533 46.0307 Mass of Unknown Liquid (grams) 0.9360 0.8498 0.9272 Volume of Unknown Liquid (mL) 1.00 1.00 1.00 Density of Unknown Liquid (g/mL) 0.936 0.850 0.928 Mean Density of Unknown (g/mL) 0.905 Average Deviation 0.003 Error (%) 0.3

The unknown substance was found to have a density of 0.905 ± 0.003 g/mL which indicates that it is ethyl acetate. The result showed an error of 0.3%.

In Part B, the density of solids were obtained and were used to calculate the density of germanium. The data from the experiment are shown in Table 1.5 below.
Table 1.5. Determination of Density of Silicon and Tin.
 Substance Silicon Tin Trial 1 Trial 2 Trial 3 Trial 1 Trial 2 Trial 3 Mass of Container (grams) 7.9042 7.9068 7.9051 8.0186 8.0170 8.0175 Mass of Container and Solid (grams) 8.2628 9.2903 9.7229 11.2019 12.1108 12.7777 Volume of Water (mL) 5.0 5.0 6.8 5.2 5.2 7.6 Volume of Water and Solid (mL) 5.3 5.6 7.2 5.6 6.4 7.9 Volume of Solid (mL) 0.3 0.6 0.4 0.4 1.2 0.3 Mass of Remaining Solid (grams) 0 0 0 0 0 0 Mass of Solid (grams) 0.3586 1.3835 1.1445 3.1833 4.0938 2.7389 Density of Solid (g/mL) 1.1953 2.3058 2.8613 7.9583 3.4115 9.1297 Mean Density (g/mL) 2.1208 6.833 Accepted Value (g/mL) 2.33 7.31 Absolute Deviation 1.1347 0.0242 0.5313 0.6483 3.8985 1.8197 Average Deviation 0.563 2.1222 Error (%) 24 29

The density obtained for silicon is 2.33 ± 0.563 g/mL with an error of 24% and that of tin was 6.833 ± 2.1222 g/mL with an error of 29%.

The calculated density of germanium based from the data above, is 4.82 g/mL ± 0.503 g/mL. The calculation was obtained as follows:

Atomic Number of Ge - Atomic Number of Si Density of Ge - Density of Si

--------------------------------------------------------- = -------------------------------------

Atomic Number of Sn - Atomic Number of Si Density of Sn - Density of Si

32 - 14 Density of Ge - 2.33

-------------- = ------------------------------

50 - 14 7.31 - 2.33
18 Density of Ge - 2.33

-------------- = ------------------------------

36 4.98

( 18 ) ( 4.98 ) = ( 36 ) (Density of Ge - 2.33 )

89.64 = 36 (Density of Ge) - 83.88
( 89.64 + 83.88 )

Density of Ge = ---------------------- = 4.82 g/mL

36
Since the accepted value is 5.323 g/mL, the calculated value has a deviation of 0.503 and an error of 9.4%. Therefore, the calculated density of germanium is 4.82 ± 0.503 g/mL.
Conclusions
The densities of acetone, ethyl acetate and hexane were 0.830 ± 0.039 g/mL, 0.967 ± 0.065 g/mL and 0.770 ± 0.11 g/mL, respectively. The errors from the determination of the densities were 4.9% for acetone, 7.2% for ethyl acetate and 16% for hexane. The unknown liquid was determined to be ethyl acetate with a density of 0.905 ± 0.003 g/mL. There was an error of 0.3%.
There was large deviation in the densities obtained for ethyl acetate and hexane. Less error was found in the density of acetone and very minimal error in the determination of the density of the unknown. The large errors could be attributed to the lack of vials. All three trials were done using only one vial which resulted to having some liquid left-over from the previous trial.
The density obtained for silicon was 2.33 ± 0.563 g/mL with an error of 24% and that of tin was 6.833 ± 2.1222 g/mL with an error of 29%. The density of germanium was calculated to be 4.82 ± 0.503 g/mL and an error of 9.4%. The errors were mostly due to lack of experience in the use of the equipment.
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