(a) A sample of tetrachloroethylene, a liquid used in dry...

(a) A sample of tetrachloroethylene, a liquid used in dry cleaning that is being phased out because of its potential to cause cancer, has a mass of $40.55 \mathrm{~g}$ and a volume of $25.0 \mathrm{~mL}$ at $25^{\circ} \mathrm{C}$. What is its density at this temperature? Will tetrachloroethylene float on water? (Materials that are less dense than water will float.) (b) Carbon dioxide $\left(\mathrm{CO}_{2}\right)$ is a gas at room temperature and pressure. However, carbon dioxide can be put under pressure to become a "supercritical fluid" that is a much safer dry-cleaning agent than tetrachloroethylene. At a certain pressure, the density of supercritical $\mathrm{CO}_{2}$ is $0.469 \mathrm{~g} / \mathrm{cm}^{3}$. What is the mass of a $25.0-\mathrm{mL}$ sample of supercritical $\mathrm{CO}_{2}$ at this pressure?

(a) A sample of tetrachloroethylene, a liquid used in dry cleaning that is being phased out because of its potential to cause cancer, has a mass of $40.55 \mathrm{~g}$ and a volume of $25.0 \mathrm{~mL}$ at $25^{\circ} \mathrm{C}$. What is its density at this temperature? Will tetrachloroethylene float on water? (Materials that are less dense than water will float.)
(b) Carbon dioxide $\left(\mathrm{CO}_{2}\right)$ is a gas at room temperature and pressure. However, carbon dioxide can be put under pressure to become a "supercritical fluid" that is a much safer dry-cleaning agent than tetrachloroethylene. At a certain pressure, the density of supercritical $\mathrm{CO}_{2}$ is $0.469 \mathrm{~g} / \mathrm{cm}^{3}$. What is the mass of a $25.0-\mathrm{mL}$ sample of supercritical $\mathrm{CO}_{2}$ at this pressure?

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Key Concepts

Density

Density is a physical property defined as the mass of a substance per unit volume. It serves as a crucial indicator of how compact the material's molecules are, and it is calculated by dividing mass by volume. Understanding density is fundamental in comparing materials and predicting behaviors such as settling or floating in different media.

Buoyancy

Buoyancy refers to the upward force that a fluid exerts on an object immersed in it. This concept is closely linked to density, as objects less dense than the surrounding fluid will typically float. Assessing buoyancy requires comparing the density of the object with that of the fluid, providing insight into whether an object will sink or float.

Supercritical Fluids

Supercritical fluids are substances that are maintained above their critical temperature and pressure, where they exhibit properties intermediate between those of liquids and gases. This state combines enhanced solvent capabilities with lower viscosities compared to liquids, making supercritical fluids useful in applications such as safe dry cleaning where traditional volatile liquids may pose health or environmental hazards.

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