9th Class Chemistry Chapter No. 6 Solutions Notes
Notes on Chapter 6 solutions for 9th Class Chemistry, Solutions are mixtures where two or more substances are evenly distributed and blended together to form a single phase. This means that the components of a solution cannot be easily distinguished and appear as a uniform mixture. Depending on the physical state of the solvent, solutions can be found in three different states: solid, liquid, or gas.
Solid solutions, like alloys, are formed when two or more metals are mixed together to create a homogeneous mixture. Liquid solutions, such as sea water, occur when a solute is dissolved in a liquid solvent, with water being the most common solvent. Gaseous solutions, like air, are formed when different gases are uniformly mixed together.
There are various types of solutions based on the combination of substances. For instance, we have gas-gas solutions like the air we breathe, which is a mixture of various gases. On the other hand, solid-solid solutions like dental amalgam are used as fillings in teeth. Liquid solutions are the most abundant because water is such a commonly used solvent. These liquid solutions vary widely, ranging from tiny raindrops to vast oceans. Interestingly, sea water, being a liquid solution, contains a rich array of 92 naturally occurring elements.
Short Answer Questions
Solutions: Solutions are homogeneous mixtures of two or more substances. They can exist in three physical states depending on the state of the solvent: solid solution (e.g., alloy), liquid solution (e.g., sea water), and gaseous solution (e.g., air). There are nine types of solutions, ranging from gas-gas solutions like air to solid-solid solutions like dental amalgam.
Aqueous Solutions: An aqueous solution is formed when a substance is dissolved in water. Water is termed the universal solvent as it dissolves a wide range of compounds. For example, sugar dissolved in water forms an aqueous solution.
Solute and Solvent: The component present in a smaller quantity is called the solute, while the component present in a larger quantity is called the solvent. In a solution with more than two substances, one acts as the solvent, and the others are solutes. For instance, in a soft drink, water is the solvent, and sugar, salts, and CO2 are solutes.
Saturated Solution: A saturated solution contains the maximum amount of solute that can be dissolved at a given temperature. Further addition of solute leads to the undissolved solute settling at the bottom. Saturated solutions achieve dynamic equilibrium, where the dissolution and crystallization of solute remain constant at a specific temperature.
Unsaturated Solution: An unsaturated solution contains a lesser amount of solute than required to saturate it at a given temperature. Such solutions have the capacity to dissolve more solute and become saturated.
Supersaturated Solution: Supersaturated solutions are more concentrated than saturated solutions. They contain an excess amount of solute beyond the saturation point. These solutions are not stable and can be obtained by preparing a saturated solution at high temperature and then cooling it down.
Dilution of Solution: Solutions can be classified as dilute or concentrated based on the relative amount of solute present. Dilute solutions contain a relatively small amount of dissolved solute, while concentrated solutions have a higher amount of dissolved solute.
Types of Solutions: Solutions can have various combinations of solute and solvent, leading to different types of solutions. These include gas-gas solutions, gas-liquid solutions, gas-solid solutions, liquid-liquid solutions, liquid-solid solutions, and solid-solid solutions.
Concentration Units: Concentration is the proportion of solute in a solution. Various concentration units are used to express the amount of solute relative to the amount of solution or solvent. Some common concentration units include mass/volume percentage, volume/volume percentage, molality, and molarity.
Long Answer Questions
What will happen if the solute-solute forces are stronger than those of solute-solvent forces?
If the solute-solute forces are stronger than those of solute-solvent forces, the solute particles will tend to stay together rather than dispersing in the solvent. As a result, the solute may not dissolve in the solvent, leading to a non-solution. Instead, the solute might form a separate phase or precipitate, depending on the conditions.
When solute-solute forces are weaker than those of solute-solvent forces? Will solution form?
When solute-solute forces are weaker than those of solute-solvent forces, a solution is more likely to form. The solute particles will be attracted to the solvent molecules, and the forces between the solute and solvent will overcome the forces between the solute particles, allowing the solute to dissolve.
Why is iodine soluble in CCI4 and not in water?
Iodine is soluble in carbon tetrachloride (CCI4) but not in water due to differences in the nature of the intermolecular forces between iodine and the two solvents.
In carbon tetrachloride (CCI4), the solvent molecules are nonpolar, and iodine molecules are also nonpolar. Nonpolar solvents like CCI4 interact with nonpolar solutes like iodine through van der Waals forces (London dispersion forces). Since iodine molecules are also nonpolar, they can easily dissolve in CCI4, which results in a solution.
In water, the solvent molecules are polar due to their dipole nature, with the oxygen end being slightly negative and the hydrogen end being slightly positive. On the other hand, iodine molecules are nonpolar. Polar solvents interact with polar solutes through dipole-dipole interactions or hydrogen bonding. Iodine cannot form strong interactions with water molecules due to its nonpolar nature, leading to its insolubility in water.
Why test tube becomes cold when KNO3 is dissolved in water?
When potassium nitrate (KNO3) is dissolved in water, it undergoes a process called dissolution, which is an endothermic process. Endothermic processes absorb heat from the surroundings to break the intermolecular forces between solute particles and to create new interactions with the solvent.
As KNO3 dissolves in water, the dissolution process requires energy in the form of heat from its surroundings. As a result, the test tube becomes cold because the heat is being absorbed from the water and the surroundings to facilitate the dissolution of KNO3. This phenomenon is known as the “heat of solution,” and it causes the temperature of the solution to decrease during the dissolving process.
What is difference between colloid and suspension?
Difference between colloid and suspension:
Colloid: A colloid is a mixture in which tiny particles of one substance are dispersed evenly throughout another substance. The particle size in a colloid is larger than individual molecules but smaller than what can be seen with the naked eye. Colloids do not settle out over time, and the particles do not dissolve completely. Examples of colloids include milk, fog, and whipped cream.
Suspension: A suspension is a mixture in which larger particles of one substance are dispersed in another substance but are not completely dissolved. The particles in a suspension are much larger and can be seen with the naked eye. Unlike colloids, suspensions can settle out over time, and the particles will separate from the liquid phase if left undisturbed. Examples of suspensions include muddy water and sand in water.
MCQ’s Notes
Can colloids be separated by filtration, if not why?
Colloids cannot be separated by filtration because the particles in a colloid are too small to be trapped by the filter paper. Filtration is effective for separating larger particles, as in the case of suspensions, but it is not suitable for colloids.
Why are the colloids quite stable?
Colloids are quite stable due to the presence of two main factors:
Brownian motion: The constant, random motion of the particles in a colloid due to collisions with molecules of the dispersion medium helps to keep the particles suspended and evenly dispersed.
Electrostatic repulsion: In some colloids, the particles carry an electric charge, which leads to electrostatic repulsion between them. This repulsion prevents the particles from aggregating or settling out.
Examples and Numerical Solution
Why does the colloid show tyndall effect?
A colloid shows the Tyndall effect, which is the scattering of light by the particles in the colloid. When a beam of light passes through a colloid, the path of the light becomes visible due to the scattering of light by the dispersed particles. This effect is not observed in true solutions or suspensions.
What is tyndall effect and on what factors it depends?
Tyndall effect depends on the following factors
Particle size: The particles in a colloid should be large enough to scatter light effectively. In solutions, where particles are much smaller, the effect is not observed.
Wavelength of light: The scattering of light is more pronounced when the wavelength of the incident light is comparable to the size of the particles in the colloid.
Identify as colloids or suspensions from the following: Paints, milk, milk of magnesia, soap solution.
Identifying as colloids or suspensions:
Paints: Colloid (dispersed pigment particles in a liquid medium)
Milk: Colloid (emulsion of fat droplets in water)
Milk of magnesia: Colloid (suspension of solid magnesium hydroxide in water)
Soap solution: Colloid (micelles of soap molecules dispersed in water)
How can you justify that milk is a colloid?
- Justification that milk is a colloid: Milk is a colloid because it exhibits the following characteristics of colloids:
- It is a heterogeneous mixture with two distinct phases: liquid (milk) and dispersed particles (fat droplets).
- The fat droplets in milk do not dissolve completely in water and remain suspended throughout the liquid due to the stabilizing action of proteins and emulsifiers present in milk.
- The Tyndall effect is observed when a beam of light passes through milk, indicating the presence of dispersed particles that scatter light.