Test: Elements, Compounds and Mixtures - Class 8 MCQ

A heterogeneous mixture is characterized by an uneven distribution of its components, making it visually separable. For example, a mixture of oil and water demonstrates this property, as the oil forms distinct layers that can be seen and separated easily.

A solution of salt in water is classified as a homogeneous mixture because the salt completely dissolves, creating a uniform composition throughout. In homogeneous mixtures, the different components are not visible, and they blend well, such as sugar in tea or salt in seawater.

A heterogeneous mixture maintains the properties of its individual components and can be separated by physical means, such as filtration or handpicking. Examples include salad, where the flavors and textures of each ingredient remain distinct.

Winnowing is primarily used to separate lighter materials from heavier ones using wind or air. This method is often employed in agriculture to separate grains from husk and chaff, effectively utilizing the natural properties of the materials to achieve separation.

Centrifugation is the technique that uses the speed of a spinning motion to separate components in a mixture based on their density. By spinning the mixture, denser components move to the bottom, allowing for easy separation of solids from liquids, such as in blood separation for medical tests.

During evaporation, a liquid component turns into gas as heat is applied, leaving behind any solid components that were mixed in. This technique is useful for recovering solids from solutions, such as obtaining salt from seawater by evaporating the water.

The role of sedimentation is to allow heavier solids to settle at the bottom of a liquid mixture. This process is important in various applications, including wastewater treatment and clarifying liquids, as it helps concentrate and remove unwanted solids from liquids.

Distillation is the method used to separate components based on their solubility and boiling points. By heating a liquid mixture, the component with the lower boiling point vaporizes first and can be condensed back into a liquid, effectively separating it from the other substances present.

Magnetic separation is the most effective method for separating iron filings from sand, as iron is magnetic while sand is not. When a magnet is brought close to the mixture, the iron filings will be attracted to the magnet, allowing for easy separation, whereas the sand will remain behind.

The main characteristic of a mixture is that its components retain their individual properties, meaning they do not chemically combine. For instance, in a salad, each vegetable maintains its taste and texture, showcasing how mixtures can involve various substances without changing their fundamental characteristics.

Filtration is the appropriate method to separate a mixture of sand and water. By pouring the mixture through filter paper, the sand (solid) is retained on the paper while the water (liquid) passes through as filtrate. This technique effectively utilizes the differences in state to achieve separation.

A pure substance is defined as a material that is made up of only one kind of atom or molecule, which means it has a constant composition and distinct chemical properties. For example, pure water is made only of H₂O molecules, whereas a mixture like saltwater contains both salt and water. This definition is fundamental in understanding the distinction between pure substances and mixtures in chemistry.

Sedimentation is the process in which heavier particles in a liquid mixture settle to the bottom due to gravity. This process is often followed by decantation, where the clear liquid above the settled solids is carefully poured off.

Noble gases are characterized by their lack of reactivity with other elements. This is due to their complete valence electron shells, which make them stable and unlikely to form bonds. Examples include helium, neon, and argon, commonly used in lighting and other applications.

The main purpose of chromatography is to separate components of a mixture based on their differing speeds as they travel along a medium, such as paper. This technique is particularly useful for analyzing complex mixtures, like inks or dyes, allowing scientists to identify and measure individual components.