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Characteristics and Factors Affecting Solutions

Learn about the characteristics of solutions and factors that affect their rate of solvation and solubility. Understand the concepts of electrolytes and Henry's Law.

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Characteristics and Factors Affecting Solutions

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  1. Solutions Ch 15 & 16

  2. What is a solution? • A solution is uniform mixture that may contain solids, liquids, or gases. • Known as a homogenous mixture • Solution = solute + solvent • Solvent – The substance in greater abundance in the solution • A solvent dissolves the solute. (dissolving medium) • Solute – The substance dissolved in the solvent

  3. Characteristics of Solutions • Soluble – The solute’s ability to dissolve in a solvent • Insoluble – The solute is not able to dissolve in a solvent • Immiscible – Two liquids that can be mixed together, but separate shortly after you stop mixing them • Miscible – Two liquids that are soluble in each other

  4. Solvation in Aqueous Solutions • Solvation – The process of surrounding solute particles with solvent particles to form a solution • Aqueous solution – A solute dissolved in water • Caused by constant, random molecular motion of solute and solvent particles. (Remember KMT) • In an aqueous solution each ion is surrounded by water molecules • Individual solute ions break away from the crystal and the charged ions become surrounded by solvent molecules (H2O) and the ionic crystal dissolves

  5. Solvation Process

  6. Rules for Solvation • Like dissolves like • Polar moleculeshave an unequal distribution of electrons • Non-polar moleculeshave an equal distribution of electrons • Polar molecules dissolve polar molecules • Non-polar molecules dissolve non-polar molecules Non-polar Molecule Polar Molecule CO2 O C H2O O O H H Equal distribution of electrons

  7. Factors that Affect Rate of Solvation (How fast something dissolves) • Need to increase collisions between solute and solvent molecules • Agitating the mixture (Stirring) • New collisions between solute and solvent will occur • Increasing the surface area of the solute (Crushing the solute) • Greater surface area allows more collisions to occur • Increasing the temperature of the solvent • Increases kinetic energy of molecules and more frequent collisions occur • Increasing the pressure (For gases) • Increases the rate of collision between particles.

  8. Solubility (How much is dissolved) • Solubility – The maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure. • Solubility is usually expressed in grams of solute per 100 g of solvent or in grams/liter.

  9. Solubility cont. . . • Saturated solution contains the maximum amount of dissolved solute for a given amount of solvent at a specific pressure and temperature. • In a saturated solution, solvation and crystallization are in equilibrium (They are happening at equal rates at the same time.) • Unsaturated solutioncontains less dissolved solute for a given temperature and pressure than a saturated solution • Supersaturated solutioncontains more dissolved solute than a saturated solution at the same temperature • A supersaturated solution is made at high temperatures, cooled slowly, and is unstable

  10. Factors That Affect Solubility (How much is dissolved) • Temperature • Most substances as temperature increases solubility increases • Gases are the exception and solubility tends to decrease as temperature increases, because they are moving quickly escaping the solvent • Pressure (For Gases Only) • The solubility of a gas in any solvent increases as the pressure above the solution increases, keeping the gas from escaping in the solvent

  11. Henry’s Law (Pressure and Solubility of a Gas) • Henry’s Law states that at a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P)

  12. Describing Solutions - Electrolytes • Electrolytes are compounds that dissociate or ionize in water to form a solution that conducts an electric current • To dissociate or ionize means to break apart into individual ions • Ionic compounds are electrolytes because they dissociate into ions • When NaCl is dissolved in water it breaks up into Na+ and Cl- ions.

  13. Electrolytes dissociate into individual ions and conduct an electric current

  14. Strong Electrolyte Weak Electrolyte Nonelectrolyte Conducts a strong current. NaCl Conducts a weak current. HgCl2 Does notconduct a current. Sugar water

  15. Strong and Weak Electrolytes • A strong electrolyte conducts a strong current and the compound has completely dissociated into ions • NaCl • A weak electrolyte conducts a poor current because only part of the solute exists as ions. • NH3 (Ammonia) • A nonelectrolyte does not dissociate or form ions, thus does not conduct a current. • Most molecular compounds are nonelectrolytes • Sucrose (sugar)

  16. Solubility Example 1 If the solubility of NaCl at 25˚C is 36.2 g/100 g H2O, what is the maximum mass of NaCl that can be dissolved in 200.0 g of H2O at the same temperature?

  17. Solubility Example 2 If the solubility of KNO3 at 20˚C is 79 grams in 250 grams of water, what is the solubility in grams per liter?

  18. Henry’s Law Example The solubility of a gas is 0.35 g/L at 25.0 kPa of pressure. What is the solubility when the pressure is increased to 115 kPa?

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