Test: Water - Grade 9 MCQ

Soft water is characterized by its ability to readily form lather with soap. It typically contains low concentrations of calcium and magnesium ions, which are responsible for hardness in water. This property makes soft water preferable for washing and cleaning applications.

Cooling a hot saturated solution is a common method to obtain crystals. As the solution cools, its ability to hold solute decreases, leading to the formation of solid crystals as the solute precipitates out of solution. This principle is widely used in crystallization processes in chemistry.

A true solution is characterized by the solute particles being so small that they do not settle and cannot be seen. The solution appears clear and transparent, and light passes through without scattering. This is important in many applications, such as in beverages and pharmaceuticals.

Water is called the "universal solvent" because it can dissolve a wide variety of substances, including solids, gases, and other liquids. This property is mainly due to its high dielectric constant, which reduces the attraction between positive and negative ions, enabling it to interact with and separate various compounds. This makes water essential for biological processes, as many chemical reactions occur in aqueous solutions.

As water freezes, it expands and becomes less dense, which is why ice floats on water. This unique property of water is crucial for aquatic life during winter, as it allows a layer of ice to form on the surface, insulating the water below and maintaining a habitable environment.

For most solids, solubility increases with an increase in temperature. This is important in various applications, including cooking and chemical processes, where higher temperatures can dissolve more solute, resulting in more concentrated solutions.

Deliquescence refers to the ability of certain substances to absorb moisture from the air, resulting in the substance becoming wet and often dissolving into a solution. This property is observed in substances like calcium chloride, which can absorb enough moisture to form a liquid solution.

The density anomaly of water allows it to be less dense when frozen, causing ice to float. This characteristic means that ice forms a layer on the surface of water bodies, insulating the liquid water beneath, which remains at a temperature that can support marine life even in cold conditions.

Increasing pressure raises the boiling point of water. This is why pressure cookers can cook food faster; they create a higher-pressure environment that allows water to boil at temperatures above 100°C, leading to quicker cooking times. Conversely, at high altitudes, like on Mount Everest, the lower atmospheric pressure causes water to boil at temperatures below 100°C.

Higher pressure increases the solubility of gases in liquids. This relationship is described by Henry's Law, which states that the amount of gas that dissolves in a liquid is proportional to the pressure of the gas above the liquid. This principle is why carbonated beverages are bottled under pressure, allowing more CO2 to dissolve.

The primary role of the water cycle is to illustrate the continuous movement and transformation of water in nature. It encompasses processes such as evaporation, condensation, precipitation, and runoff, all of which are vital for maintaining ecosystems and supporting life on Earth.

Hard water contains dissolved minerals, specifically bicarbonates, sulfates, or chlorides of calcium and magnesium. These minerals can interfere with the ability of soap to lather, leading to soap curd formation, which is an inconvenience in household cleaning.

The latent heat of vaporization for water at 100°C is 2268 J/g (or 540 cal/g). This is the amount of energy required to convert water at its boiling point into steam without changing its temperature. This high energy requirement is why steam burns can be more severe than boiling water burns.

A saturated solution is one that contains the maximum amount of solute that can be dissolved in a solvent at a specific temperature. Any additional solute added will not dissolve and will remain as a precipitate. Understanding the concept of saturation is fundamental in chemistry and various applications like cooking and industrial processing.

Efflorescence is the phenomenon where hydrated crystals lose their water to the environment, causing them to crumble into a powder. This occurs when the vapor pressure inside the crystals exceeds that of the surrounding air, leading to a dry, powdery residue.

Pure water freezes at 0°C under normal atmospheric pressure (1 atmosphere). This is a crucial temperature point in understanding water's phase changes and its role in the environment, as it influences weather patterns, aquatic life, and ecosystems.

Sublimation is the process where solid water (ice) converts directly into water vapor without first becoming liquid. This phenomenon occurs under specific conditions of pressure and temperature and is commonly observed in nature, such as in snow that seems to disappear on sunny days without melting. Understanding sublimation is important in various fields, including meteorology and physical chemistry.

Temporary hardness is primarily caused by the presence of calcium and magnesium bicarbonates in water. This type of hardness can be removed by boiling, which precipitates the bicarbonates as insoluble carbonates, making the water softer for use.

The primary component contributing to the temporary hardness of water is calcium bicarbonate. This type of hardness can be removed by boiling, which converts bicarbonates to insoluble carbonates that precipitate out of solution, making the water softer for everyday use.

Water’s high specific heat capacity means it can absorb a lot of heat without a significant change in temperature. This property helps moderate the climate of nearby land, making areas near large bodies of water experience milder temperatures. It also plays a critical role in regulating temperatures in living organisms.