Solutions Day 1 ELECTROLYTES SOLUBILITY Electrolytes STRONG AND

Solutions Day 1 • ELECTROLYTES • SOLUBILITY

Electrolytes • STRONG AND WEAK ELECTROLYTES • NONELECTROLYTES

Electrolytes • Substances that dissolve in water are classified according by whether they produce molecules or ions in solution. When an IONIC compound dissolves, the positive & negative ions separate from each other and are surrounded by water molecules. • • These solute ions are free to move, making it possible for an electric current to pass through the solution. • Electrolyte: A substance that dissolves or dissociates to ions in water that enable the solution to conduct electrical current.

Electrolytes continued Does distilled water conduct electricity? • It is a common misconception that all water conducts electrical current. • In order for a solution to conduct electricity it must contain electrolytes. • Distilled or deionized water is lacking the electrolytes needed to conduct electricity. • Bathwater contains dissolved minerals that exist as ions in solution and can conduct an electric current, while distilled or purified water does not contain ions in solution and does NOT exhibit electrolytic behavior.

STRONG & WEAK ELECTROLYTES § § § Not all electrolytes conduct an electric current the same. The more ions present in a solution the better the conductivity. When a strong electrolyte is dissolved in water, almost all the solid is dissolved and the ions separate in solution. § Ex: Salt, Na. Cl—Nearly all the Na+ and Cl- ions dissolve in solution. § Strongest electrolytes are ionic compounds that completely dissociate into ions in water.

NONELECTROL YTES Nonelectrolytes- Compounds that DO NOT conduct an electric current in either aqueous solution or in the liquid state. • Many covalent compounds are considered nonelectrolytes. • When a nonelectrolyte dissolves in water, it does not dissociate in water. • Ex: Sugar- C 6 H 12 O 6 - dissolves in water but does not produce ions, therefore it cannot conduct an electric current. • Some very polar covalent compounds are considered electrolytes when they dissolve in water.

WEAK ELECTROLYT E When a weak electrolyte dissolves in water, only a portion of the solute exists as ions. • Ex: Mercury(II) Chloride—Hg. Cl 2 Only a small portion of the Hg 2+ and Cl- ions exist in solution. Only a small current is produced •

You TESTING ELECTROLYTES can determine the presence of an electrolyte in solution by doing a conductivity test.

Factors affecting the rate of dissolution 1. SURFACE AREA 2. AGITATING 3. TEMPERATURE

Solubility of Solids Aqueous solution- Water samples that contain dissolved substances. Example: Salt water. It is a sample of water with dissolved salt. Tap water contains various amounts of dissolved minerals and gases, as does water from ponds, streams, rivers, lakes and oceans.

Dissolution • Dissolution- (Solvation)- process by which the solute dissolves in the solvent. • Rate of dissolution depends on • How quickly the solute comes into contact with the solvent and • The intermolecular forces between them. • Over time dissolution slows. • 3 things affect the rate of dissolution • Temperature, surface area, agitation

SURFACE AREA • Sugar dissolves as sugar molecules leave the crystal surface and mix with water molecules. • Because the dissolution process occurs at the surface of the solute, it can be sped up by increasing the surface area. • Small pieces dissolve faster than the same substance in large pieces. • Crushing large crystals into smaller pieces will increase the surface area in contact with the solvent, water.

AGITATING (STIRRING OR SHAKING) A SOLID IN SOLUTION • If you pour salt into a glass of water and let it sit without stirring, it will take a long time for the sugar to dissolve completely. • This is because the salt is sitting at the bottom is surrounded by dissolved sugar molecules. The surface area of the solute is low compared to the amount of solvent.

Agitating Continued • The dissolved molecules will slowly diffuse, or spread out, throughout the entire solution as they come in contact with more water, solvent. • By agitating the solution we will increase the amount of surface area of contact between solute and solvent which increases the rate of dissolution.

Heating a solvent (dissolving solids) • Sugar and other solid solutes dissolve in hot solvents more quickly than in cool solvents. • What happens to a substances energy when it is heated? • What makes the energy increase?

Dissolving solids continued • As the molecules in a solution are heated its particles move faster which increases the kinetic energy in the system. • If the molecules of the solvent are moving more quickly it will allow for more collisions between solute and solvent within a given time. • The more collisions, the quicker the solute can dissolve in the solvent.

Y Consider this Phase Diagram What process is occurring when a substance changes from point X (180 °K and 0. 03 atm) to point Y (160 °K and. 065 atm)? A) Melting (Fusion) B) Evaporation C) Deposition D) Condensation X

Which of the following processes is exothermic? A) A gas changes to a liquid B) A solid changes to a liquid C) A liquid changes to a gas D) A solid changes to a gas

Which of the following particles is an electrolyte? A) SO 2 B) Al 2(SO 4)3 C) N 2 H 4 D) CH 4

The forces that keep atoms in a molecule together are called? A) Strong Covalent Bonds B) Weak Intermolecular Forces C) Weak Ionic Bonds D) Strong Intramolecular Forces

Between points X and Y, which of the following would be observed? A) Liquid and vapor will be present X Y B) Solid and liquid will be present C) Only liquid will be present D) Only solid will be present

Consider this Phase Diagram At what temperature does the normal boiling point occur? A) 195. 3 °K B) 195. 4 °K C) 239. 8 °K D) 405. 5 °K