Solutions & Dissolving Chapter 15 Ch 15 ppt 1 - Dissolving.ppt Ch 15 ppt 1 - Dissolving.ppt

Today you will learn: What components make up a solution. General properties of aqueous solutions Precipitation reactions and solubility Factors that affect solubility Stay the same. Ch 15 ppt 3 - Dilution.ppt

Aqueous Solutions In Chemistry (especially biochemistry), many reactions take place in water. Reactions that take place in water are said to occur in an aqueous solution.

Properties of Aqueous Solutions a homogeneous mixture of two or more substances. Solute a substance in a solution that is present in the smallest amount. Solvent a substance in a solution that is present in the largest amount. In an aqueous solution, the solute is a liquid or solid and the solvent is always water.

Properties of Aqueous Solutions All solutes that dissolve in water fit into one of two categories: electrolyte or non-electrolyte. Electrolyte- a substance that when dissolved in water conducts electricity. MUST contain ions! Non-electrolyte- a substance that when dissolved in water does not conduct electricity.

Electrolytic Properties of Aqueous Solutions NaCl in water. What happens? NaCl(s) → Na+(aq) + Cl–(aq) Completely dissociates

Strong vs. Weak Electrolytes How do you know when an electrolyte is strong or weak? Take a look at how HCl dissociates in water. HCl(s) → H+(aq) + Cl–(aq) There is a single arrow showing the conversion of HCl to H+ and Cl-. This shows that in water, HCl can dissociate completely. Complete dissociation also means that the ions are hydrated and that they will never reform again. Indicates a strong electrolyte. Ch 15 ppt 1 - Dissolving.ppt

Electrolytic Properties of Aqueous Solutions Photo of hydrated ions. Ch 15 ppt 1 - Dissolving.ppt

Electrolytic Properties of Aqueous Solutions

Hydrated Ions

Electrolytic Properties of Aqueous Solutions What about weak electrolytes? What makes them weak? Ionization of acetic acid CH3COOH(aq) ↔ CH3COO–(aq) + H+(aq) (OR) HC2H3O2(aq) ↔ H+(aq) + C2H3O2–(aq) Double arrow means that the reaction is reversible. If the reaction is reversible then acetic acid is being broken down and also being reformed while in water. Since it can reform, there is not complete ionization. Complete ionization defines if an electrolyte is strong or weak. Sometimes there can be a state of chemical equilibrium……breakdown=formation. Ch 15 ppt 1 - Dissolving.ppt

Electrolytic Solutions Nonelectrolyte Weak Electrolyte Strong Electrolyte

Precipitation Reactions Precipitation Reaction- a reaction that results in the formation of an insoluble product. These reactions usually involve ionic compounds. Ex.: formation of PbI2: Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq) Double displacement reaction. Can you see where the ions switched partners? Ch 15 ppt 1 - Dissolving.ppt

Preciptate

Precipitate

Precipitation Reactions How do you know whether or not a precipitate will form when a compound is added to a solution? By knowing the solubility of the solute! Solubility- The maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. Three levels of solubility: Soluble, slightly soluble or insoluble.

Precipitation Reactions See white table on back of periodic tables

Determining Solubility Determine the level of solubility for the following: (1) Ag2SO4 (2) CaCO3 (3) Na3PO4 (1) soluble (2) insoluble (3) soluble Only Na3PO4 is soluble. Ch 15 ppt 1 - Dissolving.ppt

Solution Formation Composition of the solvent and the solute determine whether a substance will dissolve (polarity… “like dissolves like”) The factors that determine how fast a substance dissolves are: stirring temperature surface area of the solute particles

A cube of sugar in cold tea dissolves slowly. Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring. Granulated sugar dissolves very quickly in hot tea.

Stirring and Solution Formation Stirring speeds up the dissolving process because fresh solvent (the water in tea) is continually brought into contact with the surface of the solute (sugar).

Temperature and Solution Formation At higher temperatures, the kinetic energy of water molecules is greater than at lower temperatures, so they move faster. As a result, the solvent molecules collide with the surface of the sugar crystals more frequently and with more force.

Particle Size and Solution Formation A spoonful of granulated sugar dissolves more quickly than a sugar cube because the smaller particles in granulated sugar expose a much greater surface area to the colliding water molecules.

Solubility saturated solution contains the maximum amount of solute for a given quantity of solvent at a given temperature and pressure. unsaturated solution contains less solute than a saturated solution at a given temperature and pressure. solubility the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution.

Factors Affecting Solubility Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent Both temperature and pressure affect the solubility of gaseous solutes.

The solubilities of most gases are greater in cold water than in hot. Temperature SOLIDS The solubility of most solid substances increases as the temperature of the solvent increases. GASES The solubilities of most gases are greater in cold water than in hot.