Presentation on theme: "Chapter 8 Section 8.1. Formation of Solutions A solution is a homogeneous mixture of two or more substances, consisting of ions or molecules. For."— Presentation transcript:
Formation of Solutions A solution is a homogeneous mixture of two or more substances, consisting of ions or molecules. For a solution to form, one substance must dissolve in another.
Solute and Solvent Too simplify: What two things make up a solution? A solute and a solvent. What is a solute? Something that gets dissolved in a solvent. What is a solvent? Something that dissolves a solute.
Types of Solutions Solutions may exist as gases, liquids, or solids. solute The solute is the dissolved substance. In the case of a solution of a gas or solid in a liquid, it is the gas or solid. Otherwise, it is the component of lesser amount. solvent The solvent is the dissolving medium. Generally it is the component of greater amount.
Examples of Solutions TypeExampleSoluteSolvent Gas in GasAirOxygenNitrogen Gas in liquidSodaCarbon dioxide (gas) Water (liquid) Solid in LiquidSeawaterSalt (solid)Water (Liquid) Liquid in Liquid Windshield Washer AlcoholWater Solid in SolidBrassZinc (solid)Copper (solid)
Substances Dissolving in Water Three Ways: Dissociation Dispersion Ionization
Dissociation Ionic compounds metal + nonmetal (Binary and Multivalent) metal + polyatomic anion polyatomic cation + anion When ionic compounds dissolve in water the anions and cations are separated from each other; this is called dissociation We know that ionic compounds dissociate when they dissolve in water because the solution conducts electricity
Dispersion of Molecular Compounds Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water. dispersion A substance dissolves in water by breaking up into smaller pieces. These pieces of the same substance spread throughout the water. This process is known as dispersion.
Ionization of Molecular Compounds The process in which neutral molecules gain or lose electrons is known as ionization. Unlike dissociation and dispersion, which are physical changes, dissolving by ionization is a chemical change. The solution that results contains new substances.
Properties of Liquid Solutions Three physical properties of a solution that can differ from those of its solute and solvent are: Conductivity Freezing Point Boiling Point.
Conductivity The current is carried by dissolved ions The ability of an ion to carry current is a function of: Ions charge (more charge, more current) Ions mass or size (larger ions, conduct less)
Freezing Point Freezing Point Depression Lowering the freezing point of a solution as a result of the dissolved solute The presence of solute particles affects how the solvent freezes.
Boiling Point Boiling Point Elevation Raising the boiling point of a substance by adding solute
Heat of Solution During the formation of a solution, energy is either released or absorbed. Like chemical reaction, the solution process can be described as exothermic or endothermic. Dissolving sodium hydroxide in water is exothermic because it releases heat. Dissolving ammonium nitrate is endothermic because it absorbs heat. In order for a solution to form, both the attractions among solute particles and the attractions among solvent particles must be broken. In an exothermic reaction, the amount of energy required to break the attractions among the solute particles and among the solvent particles is less than the energy released as attractions form between solute and solvent particles.
Heat of Solution In an exothermic reaction, the amount of energy required to break the attractions among the solute particles and among the solvent particles is less than the energy released as attractions form between solute and solvent particles. The formation of attractions releases energy. The difference between these energies is known as the heat of solution.
Factors Affecting Rates of Dissolving Like rates of chemical reactions, rates of dissolving depend on the frequency and energy of collisions that occur between very small particles. During a chemical reaction, collisions occur between particles of the reactants. During the formation of a solution, collisions occur between particles of the solute and solvent. Factors that affect the rate of dissolving include surface area, stirring, and temperature.
Factors Affecting Rates of Dissolving Temperature If we heat particles they will move faster The solvent will carry the solute particles away faster So… Hotter Faster
Factors Affecting Rates of Dissolving Stirring or Shaking Stirring or shaking a solution moves the solute particles around so that they are closer to water particles the water particles can then attract them easily and carry them away! So…. Dissolve Faster
Factors Affecting Rates of Dissolving Surface Area When broken into small particles the water particles can then attract them easily and carry them away! When solute is broken up, there is more surface area where dissolving can occur So…smaller surface area faster dissolves