1st year Chemistry Chapter 7 Solution & Electrolytes Questions and Answers
Q.1: Why the boiling point of a solution of a non-volatile solute in a volatile solvent is always greater than the boiling point of a pure solvent?
Ans: The elevation of the boiling point of the solution is due to the lowering of vapour pressure of the solution as compared to the pure solvent. In the case of solution the vapour pressure becomes less. In order to equalize the vapour pressure of the solution to the external pressure, more temperature us required than that in the pure suite of the solvent. Which causes elevation of boiling point.
Q.2: Why a non-volatile solute in a volatile solvent lowers vapour pressure of solution?
Ans: The particles of the solute are distributed throughout the bulk of the solution and some of the particles of the solute are also present on the surface of the solution. The number of molecules of the solvents per unit area on the surface of the solution become less. Hence the evaporating tendency of the solvent decreases and vapour pressure of solution becomes less.
Q.3: Why the freezing points are depressed due to presence of solute?
Ans: The lowering of vapour pressure compels the solutions to freeze at those temperature, which are below the freezing point of pure solvent. The reason is that the vapour pressure temperature curve meets the solid phase of pure solvent at lower temperature than the pure solvent.
Q.4: Boiling poi of solvents increase due to the pressure of solute. Why?
Ans: The surface of the solution has molecules of solute as well. They do not allow the solvent to leave the surface as rapidly as in pure solvent. The boil the solutions we have to increase the temperature of solutions in comparison to pure solvents.
Q.5: Define Colligative properties? Name some important Colligative properties?
Ans: Those properties of solutions, which depend on the number of the properties. These properties are:
➤ Lowering of vapour pressure
➤ Elevation of boiling point
➤ Depression of freezing point
➤ Osmotic pressure
Q.6: What is the effect of temperature on the conjugate solution of water and phenol?
Ans: Water and phenol are partially miscible. They make two distinct solutions and two separate layers at room temperature. By increasing the temperature, the composition of the two conjugate solution change and at 65.9°C a homogeneous mixture of two components is formed.
Q.7: What is conjugate solution?
Ans: When two partially miscible liquids are mixed, two layers are produced, They are the solutions of one component into the other. These two solutions have distinct line of demarcation and are called conjugate solutions.
Q.8: What are the hydrates? How are they formed?
Ans: The crystalline substances that contain chemically combined water in definite proportional
is called a hydrate. They are produced when aqueous solution of soluble salt is evaporated.
Q.9: How the forces of attraction between the ions and the solvent molecules depend upon the charge densities of the ions?
Ans: Smaller the size of the ion or greater the amount of the positive charge on the ion, greater the charge density. Such ions have greater forces of attractions. For the molecules of the solvent. They are solved more effectively. Negatively charged ions are bigger in size, so that are not solvated in a better way.
Q.10: How the ions are stabilized when a strong electrolyte like NaCl and KCI are dissolved in H₂O?
Ans: Strong electrolyte area dissolved to the maximum extent and positive and negative ions are produced. These ions are surrounded by the water molecules as follows. Their charged are satisfied by the solvent molecules. In this way, they get the stabilities. INT
Q.11: Heat lution of a substance Is measured at infinite dilution? Why?
Ans: Actually the maximum amount of heat is evolved or absorbed, when each particle of one mole of solute is completely solved by the solvent molecules. These solvated particles of the solute should be far away from each other in the solution. This is only possible when this solution is very dilute.
Q.12: When the heat of solution in negative, then increase in temperature decreases the solubility and vice versa? Why?
Ans: When the heat of solution is negative it means that the vessel is heated up during the solution formation. So when heat is supplied from outside, then the system will go to that side where greater amount of heat can be stored and that is the side of low solubility.
Q.13: Why the NaCl and KNO, are used to lower the melting point of ice?
Ans: NaCl and KNO, are electrolytes and are sufficiently soluble in water. They double the number of particles after dissociation in water. In this way, they can manage to decrease the freezing point of water to a greater extent as compared to a non-electrolyte.
Q.14: The concentration in terms of molarity is independent of temperature, but morality depends upon temperature? Why?
Ans: In molal solutions the mass of the solvent and that of the solute are also fixed. The masses of the substances are not temperature dependent. In molar solutions are have the volume of solutions. Volume of a liquid is a temperature dependent. So the molality is not influenced by temperature but molality does change.
Q.15: The total volume of the solution by mixing 100 cm³ of water with 100 cm³ of alcohol may not be equal to 200 cm³? Justify it?
Ans: In one molal solution of urea, 60 grams of urea is dissolved in 1000 g of water, which is approximately 1000 cm³ of water. In one molar solution of urea, 60 g of urea is added in water to make total volume of solutions as 1000 cm³. So the volume of water in molar solution is concentrated and molal solution is dilute.
Q.16: Why glucose is not soluble in CCl4, but dissolve in water?
Ans: The molecule of glucose has strong hydrogen bonding due to the presence of give -OH groups, CCI, being non polar molecule solvent, cannot break the hydrogen bond ing among glucose molecules water is polar solvent, so it breaks the hydrogen bonding of glucose and dissolves it.
Q.17: What do you mean by discontinuous solubility curves?
Ans: The graph between solubilities and temperature may show a sudden change in the direction. Such a graph is called discontinuous solubility curve. Such curve is the combinations of two or more than two curves due to the changing behaviours of that compound.
Q.18: How does fractional crystallization help in removing the impurities from a solid substance?
Ans: The impure substance is dissolved in hot solvent. The solute to be purified should be less soluble than impurities. When cooling is done, this solute settle down in the form of crystals and impurities are left behind in the solution. Filtration is done to get the crystals of the required substances.