April 02, 2013

Solubility  GuidelinesWhen  you  write  a  dissociation  equation  or  any  equation  involving  ionic  compounds,  you  need  to  know  whether  a  compound  is  soluble  in  order  to  include  the  proper  state  -­‐  solid  (s)  or  aqueous  (aq)  -­‐  in  the  equation.  

Determine  the  Solubility  of  the  Following  Compounds

Compound   Soluble?  (Y/N)   Compound   Soluble?  (Y/N)  

KBr   Yes  ZBr  (aq) Sodium  Acetate   Yes  CH3COONa  

Zn(OH)2 No  ZnS  (s)   MgCO3 No  MgCO3  (s)  

Copper  Sulphate   No  CuSO4  (s)   BaSO4  No  BaSO4

April 02, 2013

Solubility

The  maximum  amount  of  solute  that  can  dissolve  in  a  given  amount  of  solvent  at  a  given  temperature

A  saturated  solution  has  the  maximum  amount  of  dissolved  solute  at  a  given  temperature

An  unsaturated  solution  can  dissolve  more  solute  at  a  given  temperature

Solubility  is  usually  expressed  in  g/100mL  of  solvent  

April 02, 2013

Every  compound  has  a  unique  solubility  in  water

COMPOUND   SOLUBILITY  (g/100mL  water)

glucose   45.0

codeine  (C18H21NO3 0.79

hexane  (C6H14) 0.11

docosane  (C22H46) 0.0000006

April 02, 2013

 Example  The  solubility  of  sucrose  is  67.1  g/100mL    of  water  at  25.0℃How  much  sucrose  is  dissolved  in  250  mL  of  water?

To  Solve,  set  up  a  ratio:

The  solubility  of  sucrose  is  67.1  g/100  mL  of  water  at  25.0℃  

How  would  you  describe  a  solution  that  contained  300  grams  of  sucrose  dissolved  in  500  mL  of  water  at  25℃?

Is  the  solution  saturated  or  unsaturated?

April 02, 2013

Since  this  is  less  than  the  solubility  of  sucrose,  the  solution  is  unsaturated

Saturated  SolutionsOnce  a  solution  has  reached  the  limit  of    solubility,  the  solution  is  said  to  be  saturated-­‐This  means  that  the  solvent  can  hold  no  more  solute-­‐If  additional  solute  is  added  to  a  saturated  solution,  the  extra  solute  will  settle  out.

April 02, 2013

This  means  that  :•the  rate  of  dissolving  is  the  same  as  the  rate  of  crystallization(crystalizing  is  the  reverse  of  dissolving)  

•the  mass  of  undissolved  solute  remains  the  same

A  saturated  solution  is  in  a  state  of  equilibrium

April 02, 2013

What  mass  of  sucrose  is  in  a  beaker  containing  100mL  of  saturated  solution  and  30.0g  of  undissolved  solute?

Total  mass  =  

Total  mass  =  

Conditions  of  Equilibrium

The  system  must  be  closed  (no  matter  can  enter  or  leave)  

There  must  be  solid  and  solution  in  contact

April 02, 2013

Dissolving:  CuSO4(s)  -­‐-­‐>  

Crystallizing:                                                                                                      -­‐-­‐-­‐>

An  equilibrium  arrow  can  be  used  to  represent  an  equilibrium  process

Since  we  can't  actually  see  molecules,  we  know  that  equilibrium  happens  because  of  a  neat  experiment  involving  radioactive  iodine.

April 02, 2013

Radioactive  IodineSolid  NaI  containing  radioactive  iodine  was  added  to  a  saturated  solution  of  NaI  that  wasn't  radioactive

Over  time,  the  radioactivity  was  found  in  the  solution  even  though  the  same  amount  of  solid  remained  at  the  bottom  of  the  beaker

This  indicated  that  dissolving  was  still  taking  place  at  the  same  rate  of  crystallization

April 02, 2013

Factors  That  Affect  SolubilityA)  Temperature

The  solubility  of  most  solids  increases  with  temperatureHigher  temperature  makes  it  easier  to  break  the  intermolecular  forces  between  the  solute  and  solvent

SOLIDS

The  solubility  of  most  liquids  is  NOT  greatly  affected  by  temperature

LIQUIDS