Question

Mists are produced by (a) smoke formed during combustion of organic matter (b) particles of spray liquids and by condensation of vapours in air (c) fine solid particles produced during crushing and grinding (d) condensation of vapours during chemical reactions.

Short answer

Mists are produced by (b) particles of spray liquids and by condensation of vapours in air, and (d) condensation of vapours during chemical reactions.

Step-by-step solution

Identify the Source of Mists

Examine each option provided to determine whether it is a potential source of mist formation.

Analyze Option (a) - Smoke Formed During Combustion

Determine if smoke from combustion is a mist. Smoke is actually a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion. It is not a mist, which consists of tiny water droplets suspended in the air.

Analyze Option (b) - Spray Liquids and Condensation of Vapours

Assess whether particles of spray liquids and condensation of vapors in the air can be considered mist. These processes directly result in the formation of tiny water droplets, which is characteristic of mists.

Analyze Option (c) - Fine Solid Particles from Crushing and Grinding

Evaluate if fine solid particles produced during crushing and grinding are a form of mist. Dust produced during these activities is comprised of fine solid particles and does not involve the condensation of water vapor, hence it is not mist.

Analyze Option (d) - Condensation of Vapours During Chemical Reactions

Consider if the condensation of vapors during chemical reactions can lead to mist formation. When gaseous products condense, they can form tiny droplets which are characteristic of mists.

Key concepts

Condensation of Vapours

Condensation of vapours is a fundamental physical process where water vapor in the air is transformed into liquid water. It typically occurs when warm, humid air comes into contact with a cold surface or when the air is cooled to its dew point, the temperature at which air is saturated with moisture and can hold no more water vapor. At this point, the excess vapor begins to condense into tiny droplets.

Understanding this process is crucial, especially when considering how mists are formed. As the vapours condense, they create a visible cloud of tiny water droplets suspended in the air—this is what we commonly refer to as mist. Factors that affect condensation include temperature, humidity, and the presence of nucleation sites where condensation can begin. In the context of the textbook exercise, both spray liquids and the condensation of vapours during chemical reactions can act as sources of mist formation due to the presence of water molecules condensing into minuscule droplets.

Properties of Mists

Mists are comprised of fine droplets of liquid, typically water, suspended in the air. These droplets are larger than single molecules but small enough to remain aloft; they usually range from about 1 to 100 micrometers in diameter. The properties of a mist can vary depending on the size and density of the droplets, as well as the conditions that led to its formation.

For example, a mist generated by condensation of water vapor will often have smaller, more uniform droplet sizes compared to a mist from spray liquids, which can have a broader size distribution. The visibility in misty conditions is reduced because these droplets scatter light—this is why mist can often be seen as a faint white or grey veil. Moreover, the duration and stability of the mist can be affected by temperature, with higher temperatures potentially causing the mist to evaporate more quickly.

Combustion and Mist Formation

Smoke Versus Mist

Smoke produced from the combustion of organic matter, such as wood or fossil fuels, should not be confused with mist. While both may impair visibility, smoke consists of a mixture of gases, along with solid and liquid particulates that are byproducts of the combustion process. Unlike mist, which is primarily made up of liquid water droplets, smoke contains a range of substances including carbon particles, volatile organic compounds, and other chemical byproducts.

However, it's important to note that under certain conditions, combustion can contribute to mist formation. For instance, when combustion occurs at high humidity levels, the water vapor produced may condense into fine droplets, forming a mist in conjunction with other combustion byproducts. This demonstrates the complex interplay between combustion, water vapor, atmospheric conditions, and pollution, highlighting the need to analyze each scenario case by case to determine the nature of the resultant emission.