8.2 Factors that Affect Rate of Dissolving and Solubility
Learning Goals …
…
identify factors that affect the RATE of dissolving
…
identify factors that affect the AMOUNT of dissolving (solubility)
…
use a solubility curve to answer problems about solubility
Collision Theory: chemical reactions can only occur if reactants collide with proper
______________________ and enough ______________ ______________ to
break reactant bonds and form product bonds
Factors Affecting the Rate of Dissolving:
Temperature: ____ T _____ R
 the solvent particles have _______________ kinetic energy and therefore
collide with undissolved solute particles _______________ frequently.
Agitation:
____ A _____ R
 ________________ solvent particles come into contact with undissolved
solute particles.
Particle size:
____ SA ( _____ P) _____ R
 the amount of surface area of the solute is _________________ therefore
more exposure to the solvent.
Factors Affecting Solubility
**Like dissolves like**
_______________ solutes dissolve in ________________ solvents;
_______________ solutes dissolve in ________________ solvents
 Water can dissolve ________________ Compounds and _______________
Molecular Compounds but not ___________________ Molecular Compounds
Temperature
____ T
_____ solubility
 there is more energy to break the bonds between the solvent molecules.
Dissolving an Ionic Compound
When the force of attraction between water and the ionic compound
(____________molecular force) is stronger than the force of attraction holding the
solid ionic compound together (______________molecular force), then the ionic
compounds will __________________ and dissolve, forming a ________________.
This attraction is called an ________ ________________ ____________________.
• Ionic Compounds will have _______________ solubility if the ions are
______________ to pull apart:
Ion Size: ______ Size
______ solubility
• Larger ions are farther apart and have a weaker attraction  are easier to pull
apart (eg KCl > NaCl)
Ion Charge:
______ charge ______ solubility
• Larger charges have a stronger attraction  are harder to pull apart (eg NaCl >
MgCl2)
Dissolving a Molecular Compound
When the force of attraction between ____________ and the ___________
compound is ________________ than the force of attraction between the solid polar
compound molecules, then the polar compounds will _______________ and
dissolve, forming a solution. This attraction is called a _______________
_______________ ________________________.
Molecule size _____ size
_____ solubility
 Small molecules are _____________ soluble than large ones
Polarity
 Since water is polar it can only dissolve polar molecules, not non-polar
molecules
Rank the following in order of most soluble to least soluble:
LiOH, CH4, NaOH, Ca(OH)2
Solubility Curves
Solubility curves, show what mass of solute will dissolve in 100g of water over a range of
temperatures.
a) At 30°C approximately ____________ of
KClO3 will dissolve in 100g of water.
b) If the temperature is increased to 80°C,
approximately __________ of the substance
will dissolve in 100g of water.
c) At 80°C approximately _____ of KCl will
dissolve in 200g of water.
d) If the temperature of a KNO3 solution is
decreased from 70°C to 50°C,
approximately ______ of the substance will
recrystallize.
e) If 30 g of KCl is dissolved in 100 g of water
at 70°C, is the solution unsaturated,
saturated, or supersaturated?
HOMEWORK:
1.
How many grams of NaCl dissolves in 100 g of water at 90°C? ____________
2.
What is the temperature of a sample of water, if it can dissolve 80 g of KNO3?
_________
3.
Which of the compounds has the greatest solubility in 100 g of water at 30°C?
__________
4.
How much NH4Cl can dissolve in 500 g of water at 50°C? _____________
5.
How much NaNO3 recrystallizes when the temperature of 100 g of water decreases
from 20°C to 10°C? ____________
6.
The solubility of potassium chlorate, KClO3, is 20 g/100 g H2O at 50°C. If 45 g of
KClO3 are dissolved in 225 g of water at 50°C, the solution can be described as:
a. saturated
b. supersaturated
c. unsaturated
7.
Which compound is least soluble at 40°C? ____________________
8.
Which compounds decrease in solubility as the temperature increases?
__________________
9.
How many grams of potassium chloride, KCl, are soluble in 200 g of water at 30C?
10.
At what temperature does the solubility of sodium chloride match the solubility of
potassium chlorate?
11.
When 50 g of potassium chloride, KCl, is dissolved in 100 g of water at 50C, the
solution can be described as:
a. supersaturated
b. unsaturated
c. saturated
12.
When 70 g of potassium nitrate are dissolved in 100 g of water at 20C, the solution
can be described as:
a. supersaturated
b. unsaturated
c. saturated
13.
A solution of potassium chloride has 60 g of the salt dissolved in 200 g of water at
50C. How many more grams of the salt can be added to the solution before
reaching the saturation point?
a. 10 g
b. 20 g
c. 30 g
d. 40 g