Density Determination by Pycnometer

A Research Study Presented to theFaculty of the Department of Chemical EngineeringSchool of Engineering and ArchitectureSaint Louis University

In Partial Fulfilment of the Requirements for the DegreeBachelor of Science in Chemical Engineering

By:

Esguerra, Mark Anthony C.Galvez, Cherish Hazel S.Valencerina, Cheryl Jhette P.

August 2014

iTABLE OF CONTENTSTITLE PAGEiTABLE OF CONTENTSiiLIST OF TABLESiiiLIST OF FIGURESiiiChapert 1: INTRODUCTION1Chapter 2: DESIGN AND METHODOLOGY3Chapter 3: RESULTS AND DISCUSSION7Chapter 4: CONCLUSION AND RECOMMENDATION11REFERNCES12

iiLIST OF TABLESTable 3.1 Data Sheet10LIST OF FIGURESFigure 1.1 Weighing of Pycnometer3Figure 1.2 Drying of Pycnometer4Figure 1.3 Filling of Pycnomter with chloroform4Figure 1.4 Filling of Pycnometer with methanol6

iiiChapter IINTRODUCTION

Density is an important physical characteristic of matter. All objects have density and that density can increase or decrease as the result of actions taken on the object. The effects of density are important for the workings of the universe and for our daily lives. For example, density is in play when we pass by a puddle and see a slick of rainbow colored oil on top of the water. This is because oil is less dense than water, so it floats atop the puddle. When we climb into a tub of water and some of it is displaced, this is also the result of density. The amount of water we displace, as it turns out, is equal in volume to the space our bodies occupy. It is simple to find the density of an object and see the effect of density.In measuring the volume or capacities of vessels having odd shapes, such as the ones encountered in chemical operations, we usually resort to a different technique, that of measuring the mass of a liquid such as water or mercury sufficient to fill the vessel. These are measured through there densities. Where in density of a substance is its mass per unit volume. Density is expressed in grams per cubic centimetre or grams per millilitre. The reference substance is usually water frequently the temperature of the water at 4C, the temperature of its maximal density. On the definitions of the units of mass and capacity, it is an extremely difficult problem to determine in the first instance the volume in cubic centimetre or millilitre, of a given mass of water, which is a standard liquid. Certain comparative methods for the determination of densities are used. We have the Pycnometer method. In this method, an instrument known as pycnometer is used. Pycnometer is a vessel designed that, at a definite temperature and pressure, the fluid it contains will have a precisely fixed volume. It is weighed while filled with the standard fluid of known density and then with the fluid under examination. By proper and elaborate corrections for the buoyancy of the air and with suitable precautions during weighing, the masses of the two fluids of the same volume may be calculated. The density of the standard reference fluid being known, the volume of the vessel may be calculated and then density of the tested fluid. This method can also be used in the determination of the density of solid materials.Another method in determining the density of a liquid is by the use of the Westphal Balance. In this method, the liquid exerts a buoyant force upward on the immerse plummet. The gravitational force on the riders, placed in various positions along ht beam, opposes the buoyant force. When the beam is horizontal the force downward equals the force upward (the mass of the displaced liquid). The instrument is calibrated so that the sum of the rider moments is the density of the liquid. Aside from the Westphal Balance, hydrometers are also used in determining the density of a liquid and it is more accurate. A hydrometer is usually a glass bulb weighted with mercure and fitted with a stem carrying a scale. When properly weighted for the range of densities of the fluids under investigation, the bulb will be completely immersed and so much of the stem will be immersed that the weight of the fluid displaced by the immersed part of the stem and by the bulb will equal the weight of the hydrometer. The placement and divisions of the scale must be made by trails with liquids of known density.

Chapter 2DESIGN AND METHODOLGY

The first thing that was done in this experiment was the determination of the density of water. The students cleaned the pycnometer with hydrocholic acid and distilled water, then dried afterwards. Using the analytical balance, the pycnometer was weighed like shown in the figure below. (Figure 1.1)

Figure 1.1 Weighing of PycnometerAfter weighing, the pycnometer was filled with distilled water, then weighed again, and recorded its temperature. This will be used in the determination of the density of water. The students were also ask to compute for the weight of the water by simply subtracting the weight of the pycnometer to the weight of it with water. The volume of water was computer using the formula:Volume=mass/density. This procedure was repeated thrice then the average was determined for the final answer. For the determination of the density of chloroform, the students performed the same procedures. But before starting, they had cleaned first the pycnometer then dried it using a hair dryer(Figure 1.2)

Figure 1.2 Drying of PycnometerThe pycnometer was weighed. It was then filled with chloroform and weighed again. (Shown in the Figure below) Figure 1.3 Filling the pycnometer with chloroformThe students were again asked to determine for the weight of the empty pycnometer and the weight of the chloroform alone. The density of the chloroform was computed using the formula:

DENSITY(LIQUID) =MASS(LIQUID) DENSITY (H2O)MASS(H20)

(2.1)

This procedure was repeated three times and computed for the average of the results to get their final answer. The final test that was done was the determination of the density of methanol. Again, before starting with the experiment, the students washed the pycnometer with hydrochloric acid and distilled water then dried again. The pycnometer was weighed then filled with methanol (Figure 1.4). Like in the previous procedures, the students were again asked to determine for the weight of the pycnometer and weight of the methanol. For the computation of the density of methanol, the students used the same formula shown in equation 2.1. Figure 1.4 Filling the pycnometer with methanol The final step in every experiment is cleaning up. The students carefully followed the guidelines in handling excess liquids. But since the reagents that were used are not that toxic, students were allowed to throw these liquids in the sink. The apparatus that were used were cleaned thoroughly. All the information needed in the data sheet were filled out then submitted to the instruction.

Chapter 3RESULTS AND DISCUSSIONTable No. Data SheetTRIAL123

Reference liquid: water

Weight of empty pycnometer37.0886g37.0899g37.0927g

Weight of pycnometer with water57.1515g57.1903g57.3174g

Weight of water20.0629g20.1004g20.2247g

Temperature of water (K)297.15K298.15K298.15K

Density of water g/cm0.99730g/cm0.99705g/cm0.99075g/cm

Volume of water20.1172cm20.1599cm20.2845cm

Chloroform

Weight of empty pycnometer37.0872g37.0883g37.0890g

Weight of pycnometer with chloroform66.1545g66.1682g67.4221g

Weight of chloroform29.0673g29.0799g30.8331g

Density of chloroform1.4449g/cm1.4425 g/cm1.4954 g/cm

Methanol

Weight of empty pycnometer37.0940g37.0895g37.0921g

Weight of pycnometer with methanol53.1632g52.8891g52.9937g

Weight of methanol16.0692g15.7996g15.9016g

Density of methanol0.7988 g/cm0.7837 g/cm0.7839 g/cm

Density is an important property of matter, and may be used as a method for identification. The density of a sample represents the mass contained within a unit volume of the sample. The units of density therefore are quoted in terms of g/mL or g/cm. Density is usually determined and reported at 20C because the volume of a sample, hence the density, will often vary with temperature. In this experiment, three trials were made for a sample of water, chloroform and methanol. In every trial, the temperature is constantly changing, thus, resulting to different densities.

TRIAL 1:HOWeight of empty pycnometer = 37.0886gWeight of pycnometer with HO = 57.1515gWeight of HO = 57.1515g-37.0886g = 20.0629gTemperature (K) = 24 + 273.15 = 297.15K HO = 0.99730g/cm = M/V ; V = M/ = 20.0629g/0.99730 g/cm = 20.1172 cmCHLOROFORMWeight of empty pycnometer = 37.0872gWeight of pycnometer with chloroform = 66.1545gWeight of chloroform = 66.1545g-37.0872g = 29.0673gCHCl = (mCHCl)( HO)/(mHO) = (29.0673g)(0.99730g/cm)/(20.0629g) = 1.4449 g/cmMETHANOLWeight of empty pycnometer = 37.0940gWeight of pycnometer with methanol = 53.1632gWeight of methanol = 53.1632g-37.0940g = 16.0692gCHOH=(mCHOH)( HO)/(mHO)=(16.0692g)(0.99730 g/cm)/(20.06209g)=0.7988g/cm

TRIAL 2:HOWeight of empty pycnometer = 37.0899gWeight of pycnometer with HO = 57.1903gWeight of HO = 57.1903g -37.0899g = 20.1004gTemperature (K) = 25 + 273.15 = 298.15K HO = 0.99705g/cm = M/V ; V = M/ = (20.1004g)/(0.99705g/cm) = 20.1599cmCHLOROFORMWeight of empty pycnometer = 37.0883gWeight of pycnometer with chloroform = 66.1682gWeight of chloroform = 66.1682g -37.0883g = 29.0799gCHCl = (mCHCl)( HO)/(mHO) = (29.0799g)(0.99705g/cm)/(20.1004g) = 1.4425g/cmMETHANOLWeight of empty pycnometer = 37.0895gWeight of pycnometer with methanol = 52.8891gWeight of methanol = 52.8891g -37.0895g = 15.7996g

CHOH=(mCHOH)( HO)/(mHO)=( 15.7996g)( 0.99705g/cm)/(20.1004g)=0.7837g/cm

TRIAL 3:HOWeight of empty pycnometer = 37.0927gWeight of pycnometer with HO = 57.3174gWeight of HO = 57.3174g -37.0927g = 20.2247gTemperature (K) = 25 + 273.15 = 298.15K HO = 0.99705g/cm = M/V ; V = M/ = (20.2247g)/(0.99705g/cm) = 20.2845cmCHLOROFORMWeight of empty pycnometer = 37.0890gWeight of pycnometer with chloroform = 67.4221gWeight of chloroform = 67.4221g -37.0890g = 30.8331gCHCl = (mCHCl)( HO)/(mHO) = (30.3331g)(0.99705g/cm)/(20.2247g) = 1.4954g/cmMETHANOLWeight of empty pycnometer = 37.0921gWeight of pycnometer with methanol = 52.9937gWeight of methanol = 52.9937g -37.0921g = 15.9016gCHOH=(mCHOH)( HO)/(mHO)=(15.9016g)( 0.99705g/cm)/(20.2247g)=0.7839g/cmChapter 4CONCLUSION AND RECOMMENDATION

In the experiment performed, the computed densities vary in every trail due to the temperature differences. The difference of the temperature is due to the drying of the pycnometer using a blow dryer. The heat of the blow dryer was transferred to the pycnometer. Hence, the heat was also transferred to the water. It is recommended that if you use blow dryer in drying wait for the instrument to cool down. Using the Weld pycnometer in determining the density of liquids is an easy and quick method but it is less accurate. Rubber or glass caps may be fitted over the ends of both types of pycnometer to prevent evaporation of volatile liquids. Hydrometers, which are floats calibrated to indicate density of a liquid by the extent to which they submerge, are used for accurate work.

REFERENCESPaul M.A (1962). Measurements. Physical Chemistry, D.C. Heath and Company, United Stated of America.Williams, & Wilkins. Density and Some of its Clinical Uses. Topics in Physical Chemistry, 2nd Ed.Salzberg H.W., Morrow J.I., Cohen S.R., & Green M.E (1978). Density Measurements. Physical Chemistry Laboratory Principles and Experiments, Macmillan Publishing Co. Inc. New York.Weissberg, A. and Rossiter B.W., Physical Methods of Chemistry, Part IV, ch. 2. Wiley-Interscience, New York, 1972.