Factors that affect solubility

1. Factors that affect solubility Mrs. Kay Chem 12

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 in step three, the solute particles are said to be solvated. Hydration is when water is the solvent, and the solute particles are said to be hydrated.

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

8. Endothermic:H3 < (H1 + H2).

9. 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.

10. Two ways to form a solution 1. If there are strong mutual forces of attraction between solute and solvent particles in order to separate solute particles from each other and solvent particles from each other. 2. If there very weak forces of attraction holding solute particles together and holding solvent particles together.

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

12. Electronegativity • Atom is more electronegative, it is pulling electons closer to itself. • Atom is more electropositive, its electrons have been pulled farther away.

13. Non-polar Molecules • A non-polar molecule is one that the electrons 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. Practice: • Pg 195 Read • Pg 196 #8-10

17. Factors that affect solubility (continued)

18. 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.

19. Dipole-Dipole Forces • Dipole = polar molecule • Dipoles will change their direction so that their oppositely charged ends are near to one another. • The electrostatic attraction between the ends is dipole-dipole force

20. Ion Dipole Forces • The force of attraction between an ion and a polar molecule. • NaCl breaks up because the ion dipole with water is stronger than the attraction of Na+ to Cl-

21. 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

22. 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.

23. “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)

24. 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

25. 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)

26. 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. • 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

27. 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.

28. 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?

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