Solutions Chapter 15

Section 15.1 Forming Solutions

A solution is a homogenous mixture, a mixture in which the components are uniformly intermingled. This means that a sample from one part is the same as a sample from any other part.

The substance present in the largest amount is called the solvent The other substance or substances are called solutes Aqueous solutions are solutions with water as the solvent

Solubility When the solid dissolves, the ions are separated and dispersed throughout the solution.

When each molecule orients itself in a way to maximum polar water molecule orients itself in a way to maximize its attraction with the ions. When an ionic substance dissolves in water, it breaks up into individual cation and anions which are dispersed in the water.

Salt Dissolving Example…

Solubility of Polar Substances Water also dissolves many nonionic substances Ethanol

Substances Insoluble in Water Many substances do not dissolve in water Example: Petroleum

How Substances Dissolve For a solute to dissolve in water, a “hole” must be made in the water structure for each solute particle. Remember… Like dissolves like In other words, we observe that a given solvent usually dissolves solutes that have polarities similar to its own.

Saturated – Describes a that contains as much solute as will dissolve at that temperature Unsaturated – Describes a solution in which more solute can dissolve than is dissolved already at that temperature. Supersaturated – Describes a solution that contains more solute than a saturated solution will hold at that temperature. Concentrated – Describes a solution in which a relatively large amount of solute is dissolved in a solution. Dilute – Describes a solutions in which a relatively small amount of solute is dissolved in a solution.

Factors Affecting the Rate of Dissolving… Surface Area The greater the amount of surface area exposed to the solvent, the faster the dissolving will occur. Stirring Stirring removes newly dissolved particles from the solid surface and continuously exposes the surface to fresh solvent Temperature Higher temperatures cause the solvent molecules to move more rapidly, thus increasing the rate of the dissolving process.

Describing Solution Composition Section 15.2 Describing Solution Composition

Solution Composition: Mass %  

Solution Composition: Molarity  

Often we need to determine the number of moles of solute present in a given volume of a solution of known molarity. When we multiply the molarity of a solution by the volume (in liters), we get the moles of solute present in that sample: 𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛×𝑚𝑜𝑙𝑎𝑖𝑟𝑡𝑦=𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑥 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒

Dilution The process of adding solvent to a solution to lower the concentration of solute

𝑀 1 𝑉 1 = 𝑀 2 𝑉 2

Properties of Solutions Section 15.3 Properties of Solutions

Neutralization Reactions When we have considered the reactions in solution that result in the formation of a precipitate. Another common type of reaction is between an acid and a base.

An acid is a substance that produces a H+ ion. A base is a substance that result in the formation of OH- ions. When a strong acid and a strong base react, the reaction produces water. This is called an Neutralization Reaction

Boiling Point At STP water will freeze at 0°C and boil at 100°C. If you dissolve table salt in water how will it affect the boiling point?

Water Bubble Example…

Freezing Point Colligative Property – A property that is dependent only on the number of solute particles present in solution. Lowering the freezing point. When salt is applied to an icy road, the fact that the freezing point for the resulting solution has a lower freezing point than water is very important. When the applied salt dissolves in the thin layer of water on the surface of ice, forming a very concentrated solution, it causes the ice to melt (it lowers the freezing point of water). The same property is also used to protect automobile engines with the coolant (ethylene glycol), which raises the boiling point and lowers the freezing point of water, thereby protecting the engine from overheating and freezing.