Extensive concentration tables can be created in DS for our customers to facilitate everyday measurements. However, digital density measurement can also be of significant benefit in analysing complex solutions such as beer or fruit juices. The areometer works on the principle of buoyancy as a function of mass. The glass float sinks into the liquid sample until its massdependent weight force and the buoyancy force are in equilibrium.
The density that corresponds to the depth of immersion is shown on the scale inside the float column. An areometer is inexpensive but difficult to read in case of highly viscous or dark samples and very fragile.
It also requires a sample volume of at least ml and the maximum accuracy of 0. The pycnometer — a glass flask whose inner volume can be very precisely determined and reproduced — is a device used for measuring the gravimetric density.
You first weigh the empty flask and then the one filled with the liquid sample. The density is then calculated from the measured weight of the sample. A pycnometer can be used for a wide temperature and pressure range and is more accurate than an areometer. However, the measure ment takes several hours due to the elaborate weighing and requires skilled personnel.
Such devices are commercially-available for use at pressures up to 40 MPa over a wide temperature range. The principle of the technique is that a thin steel or quartz tube bent into the shape of a 'U' as shown in Figure 1 is set into oscillation perpendicular to the plane of the U.
The frequency of oscillation of the tube is determined by its mass which, in turn, is related to the mass of liquid contained within it. Since the frequency of oscillation is rather easily measured with high precision, accuracies in the measurement of liquid density of 1 part in 10 5 are claimed. For operation at higher pressures, these devices are unstable owing to the hydrostatic distortion of the thin-walled tube.
Considerably greater efforts must be expended to make measurements of liquid densities under such conditions. It is often necessary to resort to methods that measure the volume of a fixed mass of sample as a function of pressure [Whalley ; Dymond and Malhotra ]. Padua et al. In the gas phase, some of the techniques for measurement of density are quite different owing to the property of a gas to expand and to fill the space made available to it.
Measurements are then made by varying one quantity and determining the effect on the second. Thus, one may vary the volume and examine the resulting pressure change with the temperature constant throughout. This is the method most often employed for the determination of the second virial coefficient. At constant temperature and pressure, the density of a substance is constant. Thus, density can be used to identify an unknown pure substance if a list of reference densities is available, and the experimenter can choose a convenient amount of substance to work with when measuring density.
To measure the density of a sample of a substance, it is necessary to measure its mass and volume. Mass is typically measured using an analytical balance, a precise instrument that relies on the force exerted by the sample due to gravity. The container to hold the sample also used to measure volume is weighed and tared, so only the sample mass appears on the balance display when the sample is added to the container.
For liquids, this container is typically a volumetric flask, which has one marking that corresponds to a specific volume. The container is filled to the line with the liquid sample and weighed again after the empty flask has been tared. The measured density is the ratio of the measured mass to the volume indicated on the flask. Most solid substances are irregularly shaped, which complicates volume determination.
It is inaccurate, for example, to determine the volume of a powder by measuring its dimensions. Instead of directly measuring dimensions or using glassware like a volumetric flask, it is necessary to make use of a liquid displacement method to measure the volume of an irregularly shaped solid. A graduated cylinder containing a known volume of liquid in which the solid is insoluble is tared. The solid is added to the cylinder, and the total mass is weighed again to determine the mass of the solid.
Addition of the solid causes an upward displacement of the liquid, resulting in a new volume reading. The volume of the solid is equal to the change in volume due to liquid displacement i. As for liquids, the measured density of a solid sample is the ratio of the measured mass to the measured volume.
Subscription Required. Please recommend JoVE to your librarian. Density, defined as a substance's mass per unit volume, is an important physical property for characterizing a material or chemical system.
To obtain the density of a substance, its mass and volume are determined by measurement. This video will introduce the principles of density determination, the procedures for calculating the density of both solid and liquid substances, and some applications of density in scientific research. However, the volume of space occupied by the same mass is different for different substances, depending on their respective density. For example, a ton of bricks has the same mass as a ton of feathers, but occupies considerably less volume.
Density is obtained by dividing mass by volume. Mass can be measured with scales or balances, and is expressed in grams or kilograms. By convention, the volume of liquids and gases is often expressed in units of liters or milliliters, measured with glassware.
The dimensions of regularly shaped solids can be measured directly with rulers or calipers, which have linear units, giving volumes in units such as cubic centimeters.
One milliliter is equivalent to one cubic centimeter. The dimensions of irregularly shaped solid samples cannot be easily measured.
Instead, their volumes can be determined by submerging the solid in a liquid. The volume of the submerged solid is equal to the volume of liquid displaced. Now that you understand the concept of density, let's take a look at two protocols for accurately determining the density of a liquid and a solid.
To begin this procedure, place a clean and dry mL volumetric flask on an analytical balance. After the measurement has stabilized, tare the balance. The balance should read zero. Use a funnel to add approximately 45 mL of liquid to the flask. Do not fill to the calibration mark. Use a Pasteur pipette to carefully add the final 5 mL of liquid, just until the bottom of the liquid's meniscus touches the line on the flask.
Weigh the flask again and record the mass of the liquid. Repeat the measurements at least twice to obtain additional values to calculate an average density. The results are shown in this table. The average measured density was 0. To determine the density of an irregular solid in pellet form, add approximately 40 mL of water to a clean and dry mL graduated cylinder. Record the exact volume.
Place the cylinder on an analytical balance and tare. Add approximately 10 pellets, and record the new volume after the addition. Weigh the cylinder, water, and pellets. The mass is only the pellets, as the rest have been tared. Make at least two additional sets of mass and volume measurements to calculate an average value of the density. The density for zinc was measured for three different samples.
It was found to be 6. Note that, since the measurements were made in a graduated cylinder, which is less precise than a volumetric flask, the density has lower degree of precision.
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