Substances vary in their capacity for dissolving in a given solvent, the degree to which a solute will dissolve in a given solvent is called its solubility with respect to that solvent.
- If large amounts of solute can be dissolved, the substance is highly soluble.
- If only small amounts can be dissolved, the substance is slightly soluble.
- If the intended solute will not dissolve, the substance is insoluble.
- If a liquid solute dissolves readily in a liquid solvent, the two liquids are miscible (for example, milk and water mix together readily and therefore are miscible).
- Liquids that do not dissolve in each other are miscible (for example, salad iol does not dissolve at all vinegar).
Solid solute in liquid solvent
The solubility of solid solute in a liquid solvent varies with the temperature. In most cases, the solute becomes more soluble as the temperature of the solvent increases. For example: in making fudge, large amounts of sugar are mixed with small amount of milk; initially all of hte sugar will not dissolve in the milk, but when the mixture is heated to boiling, all the sugar dissolves.
Dilute solutions are those with a relatively low concentration of solute in solvent; solutions containing the maximum dissolvable amount of solute are called saturated solutions, solutions that contain more than maximum dissolvable solute are supersaturated.
Saturated solutions exist in a state of equilibrium, the same number of ions or molecules are leaving the solutions as are dissolving. When the equilibrium is disturbed (for example, by changing the temperature) the solute may come out of solution.
Gaseous solubility in liquid solvent
The solubility of gaseous solute in a liquid solvent depends on the pressure exerted on the gas. For example: a can containing a soft drink exerts pressure on the solution of gas and liquid that makes up the drink, opening the can releases the pressure exerted by the can and allows the escaping gas (fizz) to escape from the liquid. When the applied pressure increases, more gas dissolves in the liquid, conversely, when the applied pressure decreases, less gas remains in the liquid (the principle is known as Henry’s Law).
Scientist have devided various way of calculating the exact concentration of reactants in solution, the most common methods involve measuring the molarity, molality, normality, and percent solution (these are publicated in solution article).
Some physical properties of a solution vary with the number of solute particles dissolved in a given mass of solvent and do not depend on the chemical nature of the substances, these properties are called colligative properties colligative properties of liquid solution are its freezing point, boiling point, vapor pressure and osmotic pressure.. The
The addition of solute to a solution causes freezing point depression, for each mole of particles dissolved in 1000 grams of water, the freezing point is reduced 1,86 C. The addition of solute to a solution also causes boiling point elevation, for each mole of particles dissolved in 1000 grams of water, the boiling point increases 0,52 C. The addition of solute to a solution reduces its vapor pressure by amount proportional to the number of moles of nonvatile solute present.
Osmotic pressure of liquid solution
The addition of solute to a solution increases its osmotic pressure. Osmosis is the movement of water through a semipermeable membrane, if the membrane separates two solutions with different concentrations of solute, the water molecules tent to flow through the membrane and into the solution with the highest concentration of solute, the water will continue to flow toward the more concentrated side until the solute concentration on both sides of the membrane is equal. Osmotic pressure is the amount of pressure necessary to stop osmosis, as the concentration of solute increases, osmotic pressure increases.
If a solvent in a solution is volatile (easily forms a gas) and the solute is nonvolatile (rarely form a gas) scientist can recover the solute by boiling away the solvent, distillation is the process of boiling away a volatile solvent to recover the solute.
An electrolyte solution is a water solution (also called an aqueos solution) that is a better electrical conductor than pure water alone. An electrolyte is a substance that dissolves in water to forms ions, the ions conduct electricity through the water alone.
- Strong electrolytes are virtually totallyn ionic in water solution.
- Weak electrolytes are polar covalent substances that incompletely dissociate into charged particles in water, some of the dissolved molecules dissociate into charged ions, but most remain as whole molecules.
A nonelectrolyte is a substance that dissolves in water as whole, uncharged molecules, a nonelectrolyte does not enhance the flow of electricity through the water.