Ch 15.1 – What are Solutions? - Mini-Tutorial                                 Std 6

 

 

soluble – when substance will dissolve in a solvent (usually a solid in a liquid)

insoluble – when substance won’t dissolve in a solvent (usually a solid in a liquid)

immiscible – when two substances will not mix (usually two liquids)

miscible – when two substances (usually two liquids)

 

solvation – solute particles surrounded by solvent particles.  Like usually dissolves (is soluble) in like. 

EXAMPLE – polar substances dissolve in polar substances.  Salt which is polar dissolves in water, which is also polar.  Alcohol, which is slightly polar dissolves in water.  Sugar has polar –OH groups in several places which allow water molecules to attach by hydrogen bonds, so sugar dissolves in water. 

   The following three things make solvation go faster.  They all increase rates of collisions of the molecules:

      stirring (agitate)

      increase surface area (grind solute into fine powder)

      heat

heat of solvation – during salvation particles of solvent & solute:

1.  must make room for each other – this requires energy – this is endothermic. 

2. As mixing occurs and particles collide, particles attract each other – this gives off energy – this is exothermic. 

solubility –maximum amount of solute that will dissolve in a given amount of solvent (see Table 15-2 on p. 457).  Usually given as g solute/100 H2O.  saturated solution – solution where so much solute has been added that no more will dissolve in the solute.

   unsaturated solution – solute has been added and dissolved, but more can be still be added and will continue to dissolve.

supersaturated solution – a solution that was heated to dissolve more solute than it would take to saturate a solution.  These solutions, can be cooled and still keep the solute dissolved.  However, crystals will quickly form if you either add a small crystal of the solute or just shake the solution.  (see p. 459 for a complete explanation)

 

 

Henry’s Law: 

      relates pressure (P) (usually in atm) and solubility (S) (usually in g/L)

 

S1       S2 

---  =  ---

P1       P2