NCERT Solutions for Class 9 Science Chapter 2
Is Matter Around Us Pure
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-29
Questions No- 4
Explain the following giving examples. (a) saturated solution (b) pure substance (c) colloid (d) suspension.
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(a) Saturated solution: In a given solvent when no more solute can dissolve further at a given temperature is called saturated solution.
(b) Pure substance: A pure substance consists of a single type of particles. E.g., gold, silver.
(c) Colloid: A colloid is a solution in which the size of solute particles are bigger than that of true solution. These particles cannot be seen with our naked eyes, they are stable, e.g., ink, blood.
(d) Suspension: It is a heterogeneous mixture in which the solute particles are big enough to settle down, e.g., chalk-water, paints, etc.
(a) Saturated Solution:
Think of making a sweet lemonade. You start adding sugar to the pitcher and stirring. Initially, the sugar dissolves easily. However, as you keep adding sugar, there comes a point when no more sugar dissolves, and you notice sugar crystals settling at the pitcher’s bottom. That’s when the lemonade becomes saturated with sugar; it cannot dissolve any more sugar at that temperature.
(b) Pure Substance:
Picture a block of ice. It’s made entirely of water molecules arranged in a uniform, consistent manner. Elements like gold, silver, or compounds like table salt are similar; they consist of one type of material and cannot be broken down further into simpler substances by physical means.
(c) Colloid:
Consider a glass of milk. To the naked eye, it looks homogeneous, but under a microscope, it reveals tiny fat globules dispersed within the liquid. These fat globules aren’t fully dissolved but rather scattered throughout, creating a colloid.
(d) Suspension:
Imagine a jar filled with muddy water. The mud particles don’t dissolve in the water but remain suspended, giving the water a murky appearance. Similarly, a mix of sand in water displays particles that don’t dissolve but rather stay dispersed.
In everyday scenarios like making lemonade, observing ice, or noting the properties of milk and muddy water, we encounter the characteristics of saturated solutions, pure substances, colloids, and suspensions, providing tangible examples for better understanding.
(a) Saturated Solution: A solution in which no more of the solid (solute) can be dissolved at a given temperature is called a saturated solution. Suppose 50 gm of a solute is the maximum amount that can be dissolved in 100 gm water at 298 K. Then 150 gm of solution so obtained is the saturated solution at 298 K.
(b) Pure Substance: A pure substance consists of a single of matter or particles and cannot be separated into other kind of matter by any physical process. Pure substances always have the same colour, taste and texture at a given temperature and pressure. For example, pure water is always colourless, odorless and tasteless and boils at 373 K at normal atmospheric pressure.
(c) Colloid: Colloids are heterogeneous mixtures the particle size is too small to be seen with a naked eye, but it is big enough to scatter light. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium. Colloids are useful in industry and daily life. A colloid has the following characteristics:
• It is a heterogeneous mixture.
• The size of particles of a colloid lies between 1 – 100 nm and cannot be seen by naked eyes.
• The particles of colloid can scatter a beam of light passing through it and make the path visible.
• The particles of colloid cannot be separated from the mixture by filtration. The process of separation of colloidal particles is known as ‘centrifugation’.
• They do not settle down when left undisturbed. In other words colloids are quite stable e.g. smoke, milk, fog, cloud etc.
(d) Suspension: A ‘suspension’ is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. A suspension has the following characteristics:
• It is a heterogeneous mixture.
• The size of particles of a suspension is greater than 100 nm and is visible to naked eyes.
• The particles of suspension can scatter a beam of light passing through it.
• The particles of a suspension settle down when left undisturbed.
• The particles of a suspension can be separated from its mixture by filtration.