Test: Water - Class 8 MCQ

The water cycle refers to the continuous movement of water between the Earth's surface, water bodies, and the atmosphere. This cycle includes processes such as evaporation, condensation, precipitation, and infiltration, which are essential for maintaining the planet's ecosystems and climate.

Water covers 71% of the Earth's surface, making it essential for the survival of all living organisms. This high percentage highlights the significance of water in various ecosystems and its role in maintaining life on Earth. Interestingly, even though water is abundant, only a small fraction of it is freshwater available for human use.

A true solution is formed when a solute dissolves in a solvent without undergoing any chemical change. This means the solute remains intact at the molecular level, such as sugar dissolving in water. Understanding true solutions is vital in various scientific and industrial applications.

Chlorination is the primary method used to kill germs in drinking water after it has been filtered. This process involves adding chlorine to the water, effectively disinfecting it and making it safe for consumption. This step is crucial in preventing waterborne diseases, particularly in areas where water quality is a concern.

When pressure increases, the boiling point of water also increases. This principle is utilized in pressure cookers, which cook food faster by raising the boiling point of water, allowing food to cook at higher temperatures. This method significantly reduces cooking time and conserves energy.

In a suspension, the solute particles are larger and will settle over time if left undisturbed. This characteristic distinguishes suspensions from true solutions and colloids, which remain evenly dispersed. Suspensions can often be seen in everyday life, such as muddy water or some fruit juices.

The process of water vapor cooling and changing into liquid water is known as condensation. This occurs when water vapor in the atmosphere cools down and forms droplets, which can lead to cloud formation and precipitation. Understanding this process is key to comprehending the water cycle and its impact on weather patterns.

The cooling of the human body through sweat occurs mainly through the process of evaporation. When sweat evaporates from the skin's surface, it absorbs heat from the body, thus lowering body temperature. This is a natural thermoregulation mechanism that helps maintain a stable internal temperature.

Calcium chloride is a well-known hygroscopic substance, meaning it can absorb moisture from the air without forming a solution. This property makes it useful in various applications, such as drying agents in packaging and controlling humidity. Understanding hygroscopic substances is important for industries that require moisture control.

Hard water contains dissolved salts, primarily calcium and magnesium, which interfere with the ability of soap to lather. This results in the formation of scum, making cleaning tasks less efficient. Hard water can pose challenges in household tasks and industrial processes, leading to increased costs and maintenance issues.

The boiling point of pure water at sea level is 100°C. This temperature is critical for various cooking and sterilization processes. Interestingly, the boiling point can change with altitude; it decreases at higher elevations due to lower atmospheric pressure, affecting how food is cooked in mountainous regions.

When pressure is applied to ice, it can melt into water. This phenomenon is part of regelation, where the application of pressure lowers the melting point of ice, allowing it to transition into liquid form. This property is crucial in various natural processes, such as glacier movement.

Groundwater primarily originates from rainwater that seeps through the soil and rock layers. This natural filtration process allows groundwater to be relatively clean and safe for use. The level of groundwater is known as the water table, which can vary depending on seasonal rainfall and other environmental factors.

The high specific heat of water is due to its molecular structure, which allows it to absorb and release large amounts of heat without significantly changing temperature. This property is vital for regulating climate and supporting life, as it helps maintain stable temperatures in environments where water is present.

All of the listed substances—chlorides, sulfates, and bicarbonates of calcium and magnesium—are responsible for water hardness. Hard water can create challenges in cleaning and can lead to the buildup of scale in pipes and appliances. Understanding water hardness is important for both domestic and industrial applications.

Boiling is one of the simplest and most effective methods to purify water at home. By bringing water to a rolling boil, most pathogens are killed, making the water safer to drink. This method is particularly useful in emergency situations where access to clean water is limited.

Sedimentation involves the settling of heavier particles at the bottom of a container when water is allowed to stand. This process helps remove larger impurities before the water undergoes further purification steps like filtration and chlorination. It is a fundamental step in water treatment processes.

Potable water is defined as water that is safe to drink and free from harmful contaminants. It meets specific health standards and is essential for human health. Interestingly, while many natural water sources may appear clean, they often contain pollutants that require treatment to ensure safety for consumption.

The anomalous expansion of water is primarily due to its hydrogen bonds. As water cools to 4°C, it begins to expand instead of contracting, which is unusual for most substances. This property is crucial for aquatic life during winter, as it allows ice to float on top of water bodies, insulating the water below and providing a habitat for organisms.

Water is primarily used in hydroelectric power generation because of its movement. As water flows over turbines, it converts kinetic energy into mechanical energy, which is then transformed into electrical energy. This renewable energy source is essential for sustainable power generation and reducing reliance on fossil fuels.