Matter around us — Important Questions

Homogeneous mixture

Step 1: Brass is made by physically mixing copper and zinc metals together – no chemical reaction occurs. Step 2: Since it contains two different substances physically combined, it is a mixture. Step 3: In brass, copper and zinc are uniformly distributed throughout the alloy – you cannot see separate components. Step 4: A mixture with uniform composition throughout is called a homogeneous mixture. Step 5: Since the composition of brass can vary (it is not in a fixed ratio), and it can be physically separated, it is a homogeneous mixture (alloy), not a compound.

Centrifugation

Step 1: Cream and milk are not easily separated by simple filtration because cream particles are very fine and not trapped by filter paper. Step 2: Centrifugation uses a machine called a centrifuge that spins the mixture at very high speed. Step 3: Due to centrifugal force, the denser components (milk) move outward and settle at the bottom, while lighter cream rises to the top. Step 4: This allows easy separation of cream from milk. Step 5: This same principle is used in washing machines to remove water from wet clothes and in labs to separate blood cells from plasma.

1 nm to 100 nm

Step 1: Solutions are classified based on the particle size of the solute dissolved in them. Step 2: True solutions have the smallest particles – less than 1 nm – and appear transparent. Step 3: Colloidal solutions have particles between 1 nm and 100 nm – they appear translucent or semi-transparent. Step 4: Suspensions have the largest particles – greater than 100 nm – they appear opaque and particles settle on standing. Step 5: The particle size of colloids (1–100 nm) is large enough to scatter light (Tyndall effect) but small enough to not settle under gravity.

Difference in solubility of components in the same solvent

Step 1: In paper chromatography, a spot of the mixture (e.g., black ink) is placed on chromatography paper. Step 2: The paper is placed in a solvent which slowly moves up the paper by capillary action. Step 3: Different components of the mixture have different solubility in the solvent, so they travel different distances up the paper. Step 4: The more soluble component moves farther up, while the less soluble component stays closer to the starting spot. Step 5: This separates the mixture into its components, showing, for example, that black ink contains multiple dyes of different colours.