Question

Explain the important distinctions between each pair of terms: (a) molality and molarity; (b) ideal and nonideal solution; (c) unsaturated and supersaturated solution; (d) fractional crystallization and fractional distillation; (e) osmosis and reverse osmosis.

Short answer

Molality is the number of moles of solute per kilogram of solvent, while molarity is the number of moles of solute per liter of solution. An ideal solution obeys Raoult's law, whereas a non-ideal one deviates. An unsaturated solution contains less solute than the solvent can dissolve, a supersaturated one contains more. Fractional crystallization separates compounds by freezing point differences via cooling, while fractional distillation does so by boiling point differences via heating. Osmosis is the movement of solvent to regions of higher solute concentration through a semipermeable membrane, while in reverse osmosis, solvent moves to regions of lower concentration when external pressure is applied.

Step-by-step solution

Distinguish between molality and molarity

Molality is a measure of solute concentration and it is the number of moles of solute per kilogram of solvent. On the other hand, Molarity is also a measure of solute concentration but it is the number of moles of solute per liter of solution.

Distinguish between ideal and non-ideal solution

An ideal solution is a solution that obeys Raoult's law at all concentrations at a given temperature. Nonideal solutions are those which deviate from Raoult's law, meaning they do not obey it at all concentrations at a given temperature.

Distinguish between unsaturated and supersaturated solution

An unsaturated solution is a solution that contains less solute than the maximum amount that the solution is capable of dissolving at a specific temperature. A supersaturated solution, on the other hand, is a solution that contains more solute than the solvent can typically dissolve at a specific temperature.

Distinguish between fractional crystallization and fractional distillation

Fractional crystallization is a process of separation in which compounds with a high freezing point are separated from compounds with a low freezing point by cooling. However, fractional distillation is a process in which components in a chemical mixture are separated by boiling point differences via heating.

Distinguish between osmosis and reverse osmosis

Osmosis is the movement of solvent particles from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane. Reverse osmosis, on the contrary, is a process in which solvent molecules pass from a region of higher solute concentration to lower solute concentration when external pressure is applied on the higher concentration side.

Key concepts

Molality vs Molarity

Understanding the difference between molality and molarity is essential for various scientific calculations, as both are measures of solute concentration. Molality, denoted as mol/kg, is determined by dividing the number of moles of solute by the mass of the solvent in kilograms. It's particularly useful when dealing with temperature changes because molality is not affected by changes in volume due to its reliance on mass.

In contrast, molarity, expressed in moles per liter (M), is calculated by dividing the number of moles of solute by the volume of the solution in liters. Molarity can change with temperature because it depends on the volume, which can expand or contract with temperature variations. For instance, if a chemical reaction is exothermic and releases heat, the solution's volume might increase, subsequently altering its molarity but not its molality. This distinction is crucial when consistency in concentration is necessary despite temperature fluctuations.

Ideal vs Nonideal Solution

When examining solutions in chemistry, understanding the behavior of molecules is fundamental to predicting their properties. An ideal solution is characterized by adherence to Raoult's Law, which states that the vapor pressure of a component in a mixture is proportional to its mole fraction. Effectively, this means that in an ideal solution, the interactions among different molecules are similar to the interactions among like molecules.

A nonideal solution, on the other hand, deviates from Raoult's Law. This occurs when the intermolecular forces between the solute and solvent are either much stronger or much weaker than expected. This can result in a higher or lower vapor pressure than the one predicted by Raoult's Law. Understanding the distinction is key to predicting boiling points, vapor pressures, and osmotic pressures in practical applications.

Unsaturated vs Supersaturated Solution

When dissolving substances, the terms unsaturated and supersaturated refer to the amount of solute present in a solution. An unsaturated solution contains less solute than the maximum amount that can be dissolved in the solvent at a specific temperature. Additional solute will continue to dissolve if added to an unsaturated solution.

A supersaturated solution is one that has been manipulated to dissolve more solute than the solvent would normally accommodate at the given temperature. This is often achieved by increasing the temperature to dissolve more solute and then carefully cooling the solution. A supersaturated solution is unstable, and crystallization can occur when a 'seed' crystal or a slight disturbance is introduced. These concepts play vital roles in crystallization processes and the formation of various products, such as rock candy in food science or pharmaceuticals.

Fractional Crystallization vs Fractional Distillation

Separating mixtures into individual components is a common practice in chemistry, achieved by processes such as fractional crystallization and fractional distillation. Fractional crystallization is a technique used to separate substances based on differences in their solubilities. As the solution cools, the substance with the lower solubility crystallizes first and can be collected, leaving the more soluble substances in the solution.

Conversely, fractional distillation is based on differences in boiling points. By gradually heating a mixture, the component with the lowest boiling point will vaporize first. This vapor can be collected and condensed into a separate container. Sequentially, components with higher boiling points are vaporized and collected, allowing for their separation. Both techniques are foundational in industries such as pharmaceuticals, where purity of substances is paramount.

Osmosis vs Reverse Osmosis

The movement of water across a semi-permeable membrane is central to the processes of osmosis and reverse osmosis, key concepts in both biological systems and water purification technologies. Osmosis is a passive process where water moves from an area of lower solute concentration to an area of higher solute concentration, aiming to equalize solute levels on both sides of the membrane. Osmotic pressure drives this flow until equilibrium is reached.

Reverse osmosis, however, involves the application of external pressure to overcome osmotic pressure. This forces water from a region of higher solute concentration to an area of lower solute concentration, effectively purifying it by filtering out solutes. This process is widely used for desalination and removing impurities from drinking water. Understanding the directional flow of water in these processes is crucial for applications ranging from kidney dialysis to the production of high-quality potable water.