Chapter 7.2 & 7.3: Solutions

1. Chapter 7.2 & 7.3: Solutions • from 7.1, In a solution • solute: stuff dissolved • solvent: it’s dissolved in • Called the universalsolvent, because almost everything dissolves in water (not because our bodies are mostly water or the Earth is 75% water) • Water • Polar compound:oxygen keeps the electrons a little more than hydrogen does, so it has a little bit of charge on each end • “uneven distribution of electrons” … not equally shared, so has charge

2. Dissolving Process • in water, the partial charge helps pull molecules apart, making more room for interactions between molecules • breaking apart gives more surface area for interactions between molecules • stirring/shaking moves molecules away, making more room for interactions between molecules • heating makes molecules move faster so there’re more interactions between molecules

3. Hydrogen Bonding • Because water is polar, it forms hydrogen bonds between atoms • Not a bond within one molecule, e.g. between the hydrogen and oxygen • A bond between 2 atoms…hydrogen of 1 water is attracted to oxygen of another because water is polar.

4. Nonpolar compounds • no partial charges • “electrons evenly distributed” … evenly spread out, so no charges • e.g. oil • Like Dissolves Like: • Things only dissolve in similar solvents, i.e. polar in polar and nonpolar in nonpolar.

5. Solubility and Concentration • Solubility: maximumamount of solute that will dissolve at a particular temperature and pressure (quantitatively) • also how well it dissolves in something (qualitatively) • depends on the strength of attraction between atoms • Concentration: actual amount dissolved • g solute/100mL solvent (1 mL isn’t a lot, so we use 100 mL) • a lot: concentrated • a little: dilute

6. Concentrations of solutions • unsaturated: can hold more solute, holding less than the maximum amount at that temp. • saturated: can not hold any more, holding the maximum amount at that temp. • supersaturated: hold more than normal at that temp (make by heating, adding solute and then cooling) • video: http://www.youtube.com/watch?v=XSGvy2FPfCw • http://www.youtube.com/watch?v=HnSg2cl09PI&feature=fvw

7. Factors affecting solubility • Temperature: as temp of solvent goes up, can hold more solid, but less gas • Pressure: as pressure goes up, can hold more gas • So…to dissolve more solid, increase temperature • To dissolve more gas, increase pressure

8. Solubility Curves • not in book • show how much will dissolve at a certain temperature • If you have a concentration on the line, it is saturated. It is holding the maximum it can at that temp

9. Solubility Curves • If you have a concentration above the line, it either will not stay in solution, because it is holding more than the maximum it can at that temp. Or it will be supersaturated. • If you have a concentration below the line, it is unsaturated. It is holding less than the maximum it can at that temp … you can still add more solute.

10. Solubility Curves • Note how the line for a gas looks different … as temp goes up, the gas molecules move faster and do not stay in the solution. • Sol. decreases as temp. increases