Chapter: 04. Mixtures Separations Of Mixtures
A. Tick (✓) the correct options.
Which of the following is not an example of a mixture? Which of the following is not a property of a mixture? (d) It is a pure substance. Which of the following is an example of a homogeneous mixture? Mixture of oil and water is heterogeneous because B. Assertion-Reason based Question.
Assertion: Mixtures are made up of two or more compounds.
Reason: Mixtures are formed when two or more substances are combined physically and can be separated by physical means.
(d) A is false but R is true. A. Tick (✓) the correct options.
Which of the following methods are used for separating the components of a mixture that are of different size? We do not use the method of hand-picking when (d) the mixture is present in a large quantity. Which of the following methods is used for separating undesirable substances? Sieving is used when the components of a mixture are of Magnetic separation method is not used for separating the components of (d) pulses and rice flour Which of the following substances does not sublime on heating? B. Assertion-Reason based Question.
Assertion: A mixture of husk from grains can be separated by hand picking.
Reason: Husk is lighter than grains.
(d) A is false but R is true. A. Tick (✓) the correct options.
A mixture of salt and water is separated by the process of Which of the following chemicals is used for loading? The clear liquid obtained after filtration is called Which of the following is not used as a filter? B. Assertion-Reason based Question.
Assertion: In villages, people add alum to muddy water to purify it.
Reason: Alum helps mud particles to cling together and makes them heavy.
(a) Both A and R are true and R is the correct explanation of the assertion. Short Answer Questions:
What are mixtures? What type of mixtures can be separated by hand picking? Mixtures are two or more pure substances (elements or compounds) mixed together physically in any proportion, without chemical change, and retaining their individual properties. Hand-picking is used to separate mixtures where the components are different in size, colour, and shape, and the mixture is in a small quantity, or the component to be separated forms a small portion of the mixture. Define: (a) sublimation, (b) deposition and © evaporation. (a) Sublimation: The process during which a solid directly changes into its gaseous state on heating. (b) Deposition: The process during which a gas directly changes into its solid state on cooling. © Evaporation: The process during which a liquid changes into its vapour on heating (below the boiling point). Name a traditional method that can be used to separate flour and bran. What is loading? How does it help in purification of water? Loading is a process in which a chemical substance like alum is added to a mixture of solid and liquid to help the solid particles settle down faster. It helps in purification by making fine, light solid particles (like clay) form heavier clusters with alum, which then settle down more quickly, thus clarifying the water. Name the methods used to separate the components of the following mixtures: (a) Sand and water: Sedimentation and Decantation or Filtration. (b) Iron and stones: Magnetic Separation. © Husk and wheat grains: Winnowing. (d) Rice flour and pulses: Sieving. How will you separate the components of a mixture of iron filings, chalk powder and common salt? Magnetic Separation: Use a magnet to separate the iron filings from the mixture. Dissolution: Add water to the remaining mixture of chalk powder and common salt. The common salt will dissolve, while the chalk powder will not. Filtration: Filter the mixture. The undissolved chalk powder will remain as residue on the filter paper, and the salt solution will pass through as filtrate. Evaporation: Heat the salt solution (filtrate) to evaporate the water, leaving the common salt behind. How is winnowing different from sieving? Winnowing separates components based on differences in their weight or density, using wind to carry away lighter particles while heavier ones fall. Sieving separates components based on differences in their size, using a mesh that allows smaller particles to pass through while retaining larger ones. Why do we need to separate substances from a mixture? We need to separate substances from a mixture for three main reasons: to remove undesirable or harmful substances, to obtain useful components, and to get a pure sample of a substance. Long Answer Questions:
What are the characteristics of a mixture? A mixture consists of two or more substances (elements or compounds, or both) mixed together physically. It does not have any fixed composition; the components can be present in any proportion. The components of a mixture retain their individual properties. It does not have any definite property; its properties can be changed by varying the quantity of its components. It does not have fixed melting and boiling points; these depend on the proportions of its components. Its components can be separated by simple physical methods. Generally, no energy is released or absorbed during its formation. Suman mixed some salt in water by mistake. Does the salt completely dissolve in water? Suggest a method that can be used by Suman to separate salt from water. Yes, common salt (sodium chloride) generally dissolves completely in water, forming a homogeneous solution. Suman can use the method of evaporation to separate the salt from the water. She should pour the salt solution into a china dish and gently heat it over a burner. The water will evaporate, turning into water vapour, and the common salt will be left behind in the china dish as a solid residue. Application/Skill-based Questions:
Name the processes involved in the separation of sand and water from their mixture. The processes involved are Sedimentation and Decantation. Alternatively, Filtration can also be used. Referring to the image: In (a) the mixture is stirred. In (b) sedimentation occurs, where heavier sand particles settle at the bottom. In © decantation is performed, where the clear water (supernatant) is carefully poured off from the settled sand (sediment). Ruhi mixed common salt (sodium chloride) with water in a glass. She stirred the mixture for a while. Based on this information, answer the following questions: (a) Is the mixture of salt and water, a homogeneous mixture, or a heterogeneous mixture? Justify. The mixture of salt and water is a homogeneous mixture. Justification: When salt dissolves in water, its particles spread uniformly throughout the water. You cannot see the individual salt particles or water particles separately, and the composition is the same throughout the solution. (b) How can Ruhi separate the salt from the mixture? Explain. Ruhi can separate the salt from the mixture using the method of evaporation. Explanation: She can pour the salt solution into a flat-bottomed dish (like a china dish) and gently heat it. The water will absorb energy, turn into water vapour, and escape into the air. Since salt does not evaporate at this temperature, it will be left behind as a solid residue in the dish. Why is air a mixture and water a compound? Air is a mixture because: It consists of various gases (like nitrogen, oxygen, carbon dioxide, noble gases) and other particles (like water vapour and dust) that are physically mixed, not chemically combined. Its components retain their individual properties (e.g., oxygen supports burning, nitrogen is unreactive). Its composition is variable (e.g., humidity changes, presence of pollutants varies). There is no significant energy change during its formation. Its components can be separated by simple physical methods (e.g., fractional distillation of liquid air). Water is a compound because: It is formed by the chemical combination of hydrogen and oxygen elements. Its components (hydrogen and oxygen) are combined in a fixed proportion by mass (1:8). 
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