Question

Pure water can be obtained from sea water by: (a) Plasmolysis (b) Sedimentation (c) Centrifugation (d) Reverse osmosis

Short answer

Pure water can be obtained from sea water by reverse osmosis (d).

Step-by-step solution

Understanding the Question

We need to determine which method can be used to purify water from sea water and obtain pure water. Each of the options provided are different processes that have specific uses in filtering or separating components.

Reviewing Plasmolysis

Plasmolysis is a process that occurs in plant cells where the cell membrane pulls away from the cell wall due to water loss through osmosis. This process is not used for obtaining pure water from sea water.

Reviewing Sedimentation

Sedimentation involves letting particles settle out of a liquid by gravity. While this process can be used for separating particles from a liquid, it is not effective for filtering dissolved salts from sea water to obtain pure water.

Reviewing Centrifugation

Centrifugation separates components in a mixture based on density by spinning it at high speeds. This process is typically used for separating solids from liquids or separating different liquids, but it is not suitable for removing dissolved salts from water.

Reviewing Reverse Osmosis

Reverse osmosis is a water purification method that uses a semi-permeable membrane to remove ions, molecules, and larger particles such as salts from water. This process is effective for obtaining pure water from sea water.

Choosing the Correct Option

Given the explanations for each option, reverse osmosis is the process suitable for obtaining pure water from sea water.

Key concepts

Water Purification Methods

Water purification is essential to ensure safe and clean water for drinking and other uses. There are multiple methods used for purifying water, each suited to different needs and types of impurities. Here are some common methods:

• Coagulation and Flocculation: Chemicals are added to water to form larger particles, which can be easily filtered out.
• Settling and Sedimentation: The water is left still, allowing suspended particles to settle at the bottom due to gravity.
• Filtration: Water is passed through filters made from sand, gravel, or membranes to remove impurities.
• Disinfection: This process involves adding chlorine or using ultraviolet light to kill bacteria and other microorganisms.

Among these, techniques like reverse osmosis are particularly effective for removing dissolved substances such as salts, which is crucial in desalinating sea water.

Sea Water Desalination

Desalination is the process of removing salt from sea water to make it suitable for consumption and other applications. This is especially important in arid regions or places with limited fresh water sources. The two most common desalination technologies are:

• Distillation: Involves heating sea water to produce steam and then condensing it back into water, leaving the salts behind.
• Reverse Osmosis: Uses a high-pressure pump to push water through a semi-permeable membrane, filtering out salts and other impurities. It is highly effective for producing fresh water.

Reverse osmosis is favored in modern applications for its efficiency and ability to produce a large amount of potable water while requiring less energy compared to distillation.

Membrane Filtration Techniques

Membrane filtration is a key technique in separating impurities from water. It employs a semi-permeable membrane to filter out unwanted components based on size and nature.

• Microfiltration: Removes larger particles and microorganisms but not dissolved substances.
• Ultrafiltration: Filters out smaller particles, including most proteins and pathogens, but not ions and small molecules.
• Nanofiltration: Eliminates even smaller particles and some divalent ions but allows monovalent ions like sodium to pass.
• Reverse Osmosis: The most stringent filtration, capable of removing almost all dissolved salts, requiring high pressure to function effectively.

Each technique serves different purposes and is chosen based on the specific needs of the water purification process being conducted.