Chapter 7.2 & 7.3: Solutions

• from 7.1, In a solution– solute: stuff dissolved– solvent: it’s dissolved in

• Called the universal solvent, 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

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

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 .

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.

Solubility and Concentration• Solubility: maximum amount 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

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

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

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

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.

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