1. Advanced Chemistry Notes Solution Notes

2. Solutions Solutions – homogeneous mixtures of two or more substances Made up of: –Solvent – substance that does the dissolving –Solute – substance being dissolved Examples of Solutions –Kool-Aide: water – solvent, sugar – solute –Pop: water – solvent, carbon dioxide – solute

3. Solutions Types of Solutions Liquid – Solid solution –Ex: salt water Liquid – Liquid solution –Ex: hydrochloric acid and water Miscible – when two liquids mix Immiscible – when two liquids will not mix Liquid – Gas solution –Ex: oxygen and water

4. Solutions Other types of Solutions Solid – Solid solutions –Brass alloys Solid - Liquid solutions –Gold dissolves Mercury Solid – gas solutions –Palladium dissolves hydrogen Gas – Gas solution –air: O 2, N 2, Ar

5. Creating Solutions The dissolving process consists of three steps Dissociation Solvation Diffusion

6. The Dissolving Process The Dissolving Process (Ex: sugar and water) 1. Dissociation Attractive forces between solute molecules must be overcome. Water pulls sugar apart molecule by molecule

7. The Dissolving Process 2. Solvation Positive ends of solvent molecule attach to negative ends of solute molecule and vise versa. Water molecules surround and interact with sugar molecules. Water molecules remove sugar molecules from the crystal –Dispersion and dipole forces are at work here

8. Solvation

9. The Dissolving Process

10. When the solvent is water the solvation process is called hydration.

11. The Dissolving Process 3. Diffusion Random molecular movement spreads solute through out the solution Sugar molecules are evenly dispersed throughout the water

12. Factors Influencing Dissolving Factors that influence that rate at which a substance dissolves –Temperature –Stirring –Large surface area of solute exposed to solvent How does this relate to putting sugar in your coffee?

13. Solvent Selectivity What will and will not dissolve? G R of T  Like dissolves Like Polar substances dissolves other polar substances –Polar – ionic and polar covalently bonded compounds have dipoles H 2 O and HCl

14. Solvent Selectivity Non-polar substances dissolve other non- polar substances –Non-polar compounds lack dipoles CO 2 and N 2 Oil and Soap Exceptions to the rule –Chalk (CaCO 3 ) does not dissolve in water –Why? Both are polar. Water has to be able to overcome chalks (CaCO 3 ) intermolecular attractive forces to dissolve it – it can’t Chalk (CaCO 3 ) is to tightly bonded intermolecularly

15. Solubility How much solute can a substance hold? Unsaturated solution – the solvent could dissolve more solute under standard conditions

16. Solubility Saturated solution – when solvent can hold no more solute at a given temperature. –When solution is saturated some of the solute remains at the bottom of the glass. Dissolving and precipitating occur at equal rates. This is called Dynamic Equilibrium. –H 2 O(l) + NaCl(s) == Na + (aq) + Cl - (aq)

17. Solubility Supersaturated – solution holds more solute than it would at standard conditions

18. Solubility Temperature and Solubility When temperature is increased solubility also increases Consider the endothermic reaction below (solid dissolved in liquid) KClO 3 (s) + H 2 O(l) + heat == K + (aq) + ClO 3 - (aq) –Heat acts as a reactant (needs heat to dissolve) Adding heat increases solubility  makes more solution

19. Solubility

20. Temperature and Solubility When temperature is increased solubility decreases Consider the exothermic reaction below (liquid dissolves a gas) CO 2 (g) + H 2 O(l) == Heat + CO 2 (aq) –Heat acts as a product (gives off heat) Adding heat decreases solubility –What holds more carbonation – warm or cold pop?

21. Solubility Pressure and Solubility Effects of pressure on the solubility of liquids and solids are minimal. Effects of pressure on the solubility of gases are drastic. –Henry’s Law – the solubility of gases increases with the partial pressure of gases above the solution. EX: Pop – when you open a can of pop the result is the carbon dioxide escaping from the solution because the partial pressure of the gases above the pop decreases.

22. Solubility and Pressure

23. Solutions Summary Components of a solution The dissolving process –Factors affecting dissolving Process Solvent Selectivity Solubility –Unsaturated / saturated /supersaturated –Temperature / Pressure