Factors that Affect Solubility

1. Factors that Affect Solubility Chemistry 12 Ms. Withrow March 2009

2. Formation of a Solution • Step 1: Solute particles must separate from each other. Since energy must be absorbed to overcome the forces of attraction between solute particles, this process is endothermic.

3. Step 2: Solvent particles must separate from each other. Since energy must also be absorbed to overcome the forces of attraction between solvent particles, this is endothermic.

4. Step 3: Solvent particles surround and attach themselves to solute particles. These attractions release energy just like when ionic or covalent bonds are formed, but not as much energy. This is exothermic.

5. Solvation is when no particular solvent is mentioned, the solute particles are said to be solvated. Hydration is when water is the solvent, and the solute particles are said to be hydrated.

6. Heat of Solution, ΔHsoln The sum of all of the ΔH’s for the three steps involved in the formation of a solution. ΔHsoln = ΔHstep 1 + ΔHstep 2 + ΔHstep 3 Exothermic: H3 > (H1 + H2)

7. Endothermic:H3 < (H1 + H2)

8. Solutions • They are a physical change. • There are no new substances being produced • The particles of the solute and solvent merely physically mix and do not undergo a chemical change.

9. Two ways to form a solution One: There are strong mutual forces of attraction between solute and solvent particles • The particles of solute will separate from each other • The particles of solvent will separate from each other • This is due to the strong attraction

10. Two ways to form a solution Two: If there are very weak forces of attraction holding solute particles together and holding solvent particles together • The particles of solute will separate from each other • The particles of solvent will separate from each other • This is due to weak attraction

11. Polarity • This applies to molecules (two or more non-metals covalently bonded together) • Although they are sharing e-, one atom will attract the shared e- more closely, making it slightly more negative, and the other atom slightly more positive.

12. Electronegativity • An atom is more electronegative, if it is pulling e- closer to itself. • Atom is more electropositive, its e- have been pulled farther away.

13. Non-polar Molecules • A non-polar molecule is one that the e- are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.

16. Solution Equilibrium • When a solute comes out of a solution this process is called crystallization. • A dynamic equilibrium exists if the rate that the solute dissolves equals the rate the solute crystallizes.

17. Review VESPR and Polarity • Pg 194-196 Read • Pg 196 #8-10 • Pg 201 #1, 2, 5, 6

18. Factors that Affect Solubility Day Two

19. Intermolecular Forces • Forces binding atoms in a molecule are due to chemical bonding • Intramolecular forces: forces that bond the atoms to each other within the molecule.

20. Dipole-Dipole Forces + – H Cl + – + – + – + – Dipole is a polar molecule These molecules will orient themselves so that oppositely charged ends of molecules are near to one another The electrostatic attractions between these ends are called dipole-dipole forces Lets see it!

21. Ion-Dipole Forces The force of attraction between an ion and a polar molecule (a dipole) Example: NaCl breaks up because the ion dipole with water is stronger than the attraction of Na+ to Cl- Let’s See it!

22. London (dispersion) Forces • Weakest intermolecular force between non polar molecules • It is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles

23. Hydrogen Bonding • Hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule.

24. “Like Dissolves Like” • Ionic solutes dissolve in polar solvents • (ex: NaCl and H2O) • Non polar solutes dissolve in non polar solvents • (ex: solid I2 and liquid Br2)

25. Ionic solutes WILL NOT dissolve in non polar solvents • Non polar solvent cannot attract the particles of the ionic compounds strongly enough to separate them • Non polar solutes WILL NOT dissolve in polar solvents

26. Ways to increase rate of dissolving: • Use greater temperatures (more kinetic energy = more movement = more collisions being successful) • Agitating the mixture (brings new solvent into contact more quickly with undissolved solute) • Breaking up the solute ( smaller pieces = more surface area = more successful collisions)

27. Pressure • Pressure affects only the solubility of gases since liquids and solids are virtually incompressible. • High pressure pushes gas molecules close together and makes them more likely to bond with a liquid solvent. Thus, higher pressure makes gases more soluble.

28. An increase in pressure (for a gaseous solution) means that more gas has been forced into a smaller volume, so greater chances of successful collisions. • A decrease in pressure means not as much solubility

29. Why is it dangerous for deep-sea divers to come up to the surface rapidly? • At deep depths, the pressure is very high, since there is water piled up above the diver. This high pressure causes N2 to be more soluble in the blood than at normal pressures. • When the diver surfaces, the pressure is lowered, and the N2 is less soluble. This may lead to bubble formation in the blood, a dangerous, painful and potentially life-threatening condition, known as “the bends.” This may be prevented by slow decompression, so that N2 slowly leaves the blood without the formation of bubbles.

30. Try tonight, putting a cold glass of water by your bed, observe the water in the morning. • What does it look like? Did you expect this based on solubility of gases in liquids related to temperature change?

31. Practice: • Read pages 243-254 • Page 254 # 1-5