(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 g and a volume of 25.0 mL at 25 °C. What is its density at this temperature? Will tetrachloroethylene float on water? (Materials that are less dense than water will float.)

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780137542970

Verified step by step guidance

Step 1: Understand the formula for density. Density (\( \rho \)) is defined as mass (\( m \)) divided by volume (\( V \)). The formula is \( \rho = \frac{m}{V} \).

Step 2: Identify the given values in the problem. The mass of tetrachloroethylene is 40.55 g, and the volume is 25.0 mL.

Step 3: Substitute the given values into the density formula. Use \( \rho = \frac{40.55 \text{ g}}{25.0 \text{ mL}} \).

Step 4: Calculate the density using the substituted values. This will give you the density of tetrachloroethylene in g/mL.

Step 5: Compare the calculated density of tetrachloroethylene to the density of water, which is approximately 1.00 g/mL at 25 °C. If the density of tetrachloroethylene is less than 1.00 g/mL, it will float on water; otherwise, it will sink.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Density

Density is defined as the mass of a substance divided by its volume, typically expressed in grams per milliliter (g/mL) for liquids. It is a crucial property that helps determine how substances interact with each other, particularly whether they will float or sink in a given medium, such as water.

Buoyancy

Buoyancy refers to the ability of an object to float in a fluid, which is determined by the object's density relative to the fluid's density. An object will float if it is less dense than the fluid it is placed in; conversely, it will sink if it is denser. This principle is essential for understanding the behavior of tetrachloroethylene in water.

Phase-out of Chemicals

The phase-out of chemicals like tetrachloroethylene is often driven by health and environmental concerns, particularly their potential carcinogenic effects. Understanding the implications of using such substances is important in chemistry, as it relates to safety regulations and the search for safer alternatives in industrial applications.

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Textbook Question

(b) Carbon dioxide (CO₂) 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 CO₂ is 0.469 g/cm³. What is the mass of a 25.0-mL sample of supercritical CO₂ at this pressure?

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