Solubility and the Dissolving Process

1. Considering the neutralization with a strong monohydroxybase, what volume of 5.00 M sulfuric acid is needed to create 2.85x1024 water molecules?

2. Solubility and the Dissolving Process

3. Solubility and Polarity • Solubility – the ability of one substance to dissolve into another at a given temperature and pressure; • expressed in terms of the amount of solute that will dissolve in a given amount of solvent to produce a saturated solution. • Polar compounds tend to dissolve in other polar compounds and nonpolar dissolve in other nonpolar compounds.

4. Solubility and Polarity • “Like dissolves Like” • Miscible – describes two or more liquids that are able to dissolve into each other in various proportions. • If two substances are immiscible, than they will not mix together.

5. Solubilities of Solids • The greater the surface area, the faster the dissolving process. • Dissolving only takes place at the surface of substances. The solvent cannot penetrate the solute, which make it take longer to dissolve bigger “chunks” • Shaking will also increase the speed. Why?

6. Temperature • Solubilities of solids generally increase with temperature. • Increasing the temperature increases the speed of the molecules which increases the number of collisions. This speeds up the solvent’s ability to dissolve the solute.

7. Breaking Down an Ionic Compound • The dissolving of an ionic compound involves a unique factor • The separation of ions from the lattice into individual dissolved ions. • Dissociation – the separating of a molecule into simpler molecules, atoms, radicals, or ions. • If water is the solvent then the dissociation involves hydration. • Hydration – the surrounding of the dissociated ions by water molecules.

8. Enthalpy and Entropy • The dissociation process takes a large amount of energy to rip apart the lattice. • A large positive enthalpy change, ________, the water then surrounds it which has a large negative ΔH which nearly cancel out. • As ions are scattered and broken apart, the entropy ____________. Then the water surrounding and reorganizing the ions __________ the entropy, nearly cancelling out.

9. Enthalpy and Entropy • The net result of all of the enthalpy and entropy changes that accompany the dissolving process determines the solubility of an ionic solid. • This study gave us our solubility rules. • Tells is substances are soluble or insoluble in water. • Other solvents may be used if needed.

10. Saturation • When the maximum amount of solute is dissolved in solution, the solution is said to be a saturated solution. • If more can be added than is it a unsaturated solution. • Unsaturated Solution – a solution that contains less solute than a saturated solution and that is able to dissolve addition solute.

11. Exceeding Solubility • A supersaturated solution is a solution holding more dissolved solute than what is required to reach equilibrium at a given temperature. • How can we coax the solvent to take in more solute?

12. Equilibrium • Solubility Equilibrium – the physical state in which the opposing processes or dissolution and crystallization of a solute occur at equal rates. • The ions are leaving the solid surface at the same rate as ions are also returning to the pile of excess solute at the bottom of the solution. • Gases can also be dissolved in liquids • i.e. soda

13. Pressure and Temperature • Henry’s Law states that the solubility of a gas increases as the partial pressure of the gas on the surface of the liquid increase. • When you open a bottle of soda the pressure is released and the solubility decreases, allowing the gases to escape and making your soda go “flat”

14. Temperature • Warm soda has less CO2 dissolved in the liquid which also gives it a flat taste. • Gases are less soluble in a liquid of higher temperature because the increased molecular motion in the solution allows gas molecules to escape their loose arrangement with the solvent molecules. • They Break Free

15. Concept Check • Why is ethanol miscible in water? • Why do sugar cubes dissolve more slowly in water than granulated sugar? • What factors are involved in determining the solubility of an ionic salt? • You keep adding sugar to a cold cup of coffee. You stir it by eventually you notice sugar on the bottom. Explain why no more sugar dissolves.

16. Conductivity • Some substances have the ability to conduct an electric current. This depends on whether or not it contains charged particles that are able to move freely around the solution. • An electrolyte is a substance that dissolves in water to give the solution the ability to conduct an electric current.

17. Conductivity • A nonelectrolyte is a liquid or solid substance that does not allow the flow of an electric current, either in solution or in its pure state, such as water or sucrose. • Ionic salts dissociate into their individual charged ions that move around the solution freely. Would this be an electrolyte or a nonelectrolyte?

18. Acids / Bases • Strong acids COMPLETELY dissociate in water, forming the hydronium ion (H30+(aq)) • This makes all strong acids VERY good electrical conductors • Weak acids are less conductive but still dissociate to an extent. • Strong bases COMPLETELY dissociate in water, forming the hydroxide ion (_____________) • This makes strong bases also very good electrical conductors.

19. Water and Electricity • Sea water is a great conductor. Why? • Tap water is also very good because it is not distilled (still contains ions and minerals). • Do not use electrical devices by water 