Question

A pycnometer is a glass apparatus used for accurately determining the density of a liquid. When dry and empty, a certain pycnometer had a mass of \(27.314 \mathrm{~g}\). When filled with distilled water at \(25.0^{\circ} \mathrm{C}\), it weighed \(36.842 \mathrm{~g}\). When filled with chloroform (a liquid once used as an anesthetic before its toxic properties were known), the apparatus weighed 41.428 g. At \(25.0{ }^{\circ} \mathrm{C},\) the density of water is \(0.99704 \mathrm{~g} / \mathrm{mL}\). (a) What is the volume of the pycnometer? (b) What is the density of chloroform?

Short answer

The volume of the pycnometer is approximately 9.519 mL. The density of chloroform is approximately 1.352 \frac{g}{mL}.

Step-by-step solution

Calculate the mass of water

Subtract the mass of the dry pycnometer from the mass of the pycnometer filled with water to find the mass of the water alone. Use the formula: mass of water = mass of pycnometer with water - mass of dry pycnometer.

Calculate the volume of the pycnometer

Use the density of water and the mass of water to calculate the volume of the pycnometer. Use the formula: volume = mass of water / density of water.

Calculate the mass of chloroform

Subtract the mass of the dry pycnometer from the mass of the pycnometer with chloroform to find the mass of chloroform alone. Use the formula: mass of chloroform = mass of pycnometer with chloroform - mass of dry pycnometer.

Calculate the density of chloroform

Use the mass of chloroform and the volume of the pycnometer (previously calculated) to find the density of chloroform. Use the formula: density = mass / volume.

Key concepts

Density of Liquids

Density is a fundamental property of materials which relates mass to a unit volume. When it comes to liquids, understanding density is essential for numerous scientific and practical applications. The density of a liquid can be calculated using the formula \( \text{density} = \frac{\text{mass}}{\text{volume}} \) where mass is the amount of matter in the liquid and volume is the space that matter occupies.

In the context of a pycnometer density determination, a pycnometer — a precise volumetric flask — is used to ascertain the density of the liquid by first measuring the mass of the pycnometer when it is filled with the liquid and then when it is empty. The difference in mass gives the mass of the liquid which, along with a known volume of the pycnometer, can be used to calculate the density. The density thus obtained is specific to the temperature at which the measurement was taken, as liquids expand or contract with temperature changes.

Mass-Volume Relationship

The mass-volume relationship is pivotal in various scientific disciplines, such as chemistry and physics. It is essential in determining the concentration of substances and their purity. Basically, the relationship shows how mass corresponds to volume; the two are inversely proportional within the calculation of density.

In a laboratory setting, the mass-volume relationship is often explored through exercises involving pycnometers. The mass of the liquid is found by weighing the pycnometer once filled with the liquid and once empty. The difference reveals the mass of the liquid alone. By dividing this mass by the pycnometer's volume, which is constant and known, one can calculate the liquid's density. Understanding these concepts is vital for interpreting the results of experiments and ensuring accuracy in scientific measurements.

Chemistry Laboratory Techniques

In a chemistry laboratory, the technique of using a pycnometer for determining the density of a liquid is considered a standard and precise method. The accuracy of this technique hinges on correct and careful calibration and measurement practices.

Several precautions are necessary when using a pycnometer: The apparatus must be clean and dry before each measurement to avoid contamination; the temperature must be controlled since densities change with temperature; careful handling is imperative to avoid loss of liquid or addition of extra mass.

Procedural Steps

• Calibrating the pycnometer with a known substance like distilled water.
• Weighing the pycnometer empty and then filled with the liquid in question.
• Calculating the mass of the liquid and then its density.

Adhering to these laboratory techniques ensures that subsequent calculations, such as the determination of the density of chloroform, are accurate and reliable.

Properties of Chloroform

Chloroform is a colorless, dense liquid with historical significance in the realm of medicine due to its use as an anesthetic. However, its use declined upon the discovery of its toxic properties and potential to cause harm to the liver, kidney, and other organs.

From a chemical perspective, chloroform (\(CHCl_3\)) is an organic compound and is considered to be slightly volatile at room temperature. The properties of chloroform, like its density, boiling point, and solubility, are important parameters in laboratory and industrial settings. Its density is typically higher than water, a property that can be precisely determined through measurements using a pycnometer as outlined in the exercise. When discussing chloroform or any chemicals, it is important for students and professionals to understand both their physical properties and the health implications associated with their use.