LEARNING TASK CHEM II ONLINE TREASURE HUNT
Implemented June 12-13,2008
TO DISSOLVE OR NOT TO DISSOLVE
( Factors Affecting Solubility of Solids in Water)
Melodie Pacio and _______
Introduction
Have you ever wonder why oil and water don’t mix while sugar and water do?
When you add sugar to your coffee, you will notice that your coffee will be
sweetened yet you will not feel nor find the sugar granules.
The same thing when you add salt crystals to water you will not find the salt
crystals and you will observe that the water will taste salty.
Why is it that Silver chloride and Barium sulfate when placed in water will not
dissolve when water is considered a general solvent? (Not a universal solvent)
Why do some solids dissolve in water and some don’t?
Why does coffee dissolves faster in hot water than in cold water? And why
refined salt dissolves faster than granulated or rock salt? These questions will
lead us to examine factors that affect solubility of solids in water through this on
line treasure hunt.
Working by pairs choose a student you have not worked with before, find the
answers to the following questions on factors affecting the solubility of solids in
water. The answers are to be found on the websites listed below. Click on the
URL provided in this activity. Read each website carefully take note that each
website is used to answer one question. Write your answers to the questions
neatly on a clean sheet of paper with your name and your partners’ name. Then,
you may move to answer the Big Question. Be sure to work together and
complete the activity in one hour. When you’re done, you should have an
overview of factors affecting solubility of solids in water.
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.
swf
Questions
1. What happens when crystals of salt is placed in water? How will you describe this
process? What about sugar in water? In what way the two processes the same or
different?
When salt crystals are placed in water, the crystals will be dissolved as
long as the solution is unsaturated. If you keep on adding salt crystals,
the solution will become saturated, thus, the salt crystals will no longer
dissolve. Salt contain positive and negative ions, which are held together
by the strong force of attraction between particles with opposite charges.
When one of these solids dissolves in water, the ions that form the solid
are released into solution, where they become associated with the polar
solvent molecules.
When sugar is placed in water, it will definitely dissolve unless the
solution is saturated. In this process, the weak bonds between the
individual sucrose molecules are broken, and these C12H22O11
molecules are released into solution.
One difference is that salt ionizes in the solution but sugar doesn’t.
2. How will a molecular (covalent) solid and ionic solid differ in their dissolving
processes?
Molecular solids dissociate to give individual molecules, while ionic solids
dissociate to give solutions of the positive and negative ions they
contain.
Examples:
MOLECULAR SOLID
H2O
C12H22O11(s)
C12H22O11(aq)
IONIC SOLID
H2O
NaCl(s)
Na+(aq) + Cl-(aq)
3. Why are some solids soluble in water and some aren’t?
Some solids are not soluble in water because only solutes or solids with
similar properties or structural features with water will be dissolved. The
solubility of solids in water depends on its nature, the temperature and
pressure.
4. Are energy bonds involve in this process? What kind of bonds are these?
1. Yes. A thermodynamic cycle constructed for the formation of a solution
shows that a solution will form when the strength of the interaction (from
dipole-dipole, van der Waals, hydrogen bonding, etc.) between solvent and
solute is greater than the energies of the separated solute and solvent. The
strength of that solute-solvent interaction is largely determined by the
structures of the solvent and the solute.
5. What might be the factors that affect solubility of solids in water? Aside from
temperature pressure and surface area.
Aside from temperature, pressure and surface area, the nature of the
solvent and the solute also affects solubility.
The melting point of the solid, and the molar heat of fusion, also
affects the solubility of solids.
6. Can you mention / cite rules to observe when dissolving solids in water?
All common salts of Group 1 elements and ammonium (NH41+) are
soluble.
All common nitrates (NO31-) and acetates are soluble.
Most chlorides, bromides, and iodides are soluble except silver, lead
(II), and mercury (I)
All sulfates are soluble except barium, strontium, lead (II), calcium,
silver, and mercury (I)
Except for those in Rule 1, carbonates, hydroxides, oxides, and
phosphates are insoluble.
All sulfides are insoluble except those of the Group 1 and Group 2
elements and NH4+.
All nitrates are soluble.
All chlorides are soluble except AgCl, Hg2Cl2, and PbCl2.
Most sulfates are soluble. Exceptions include BaSO4, PbSO4, and
SrSO4.
All carbonates are insoluble except NH4+ and those of the Group 1
elements.
All hydroxides are insoluble except those of the Group 1 elements,
Ba(OH)2, and Sr(OH)2. Ca(OH)2 is slightly soluble.
7. Using a diagram or equations, how will you illustrate dissolving process of solids in
liquid water?
a.
The bonds holding the solute particles together must be broken. This bondbreaking step requires energy.
b.
The solvent surrounds the solute particles forming bonds (intermolecular
or ionic) between the solute and solvent particles. This process is sometimes called
solvation, or if the solvent is water, it is called hydration. Since this is a bond-forming
step, this process releases energy.
c.
Finally, the cluster of solute and solvent particles are distributed evenly
throughout the mixture. This process requires energy.
Web Resources
Reasons why solids dissolve in water

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/soluble.php#why
Ionic Solids in water

http://chemistry.about.com/library/weekly/blsolubility.htm
Introduction to solubility

http://www.sparknotes.com/chemistry/solutions/solubility/summary.html
Molecular View and factors affecting solubility

http://en.wikipedia.org/wiki/Solubility
Energy involved and inter molecular forces in dissolution

http://www.utmem.edu/physpharm/.021f.html
Rate of Solutions

http://www.sciencebyjones.com/solubility.htm
Solubility Rules

http://www.sciencebyjones.com/solubilty_rules.htm
The Big Question
Look around the school and your environment; identify dissolution processes that are
taking place. Make sure to identify the factor that affects it and the rule that accompanies
with it.
You might want to present your answers in the form of a table like the one below where
you write the specific dissolution process in column 1, the factor that affects it then the
rule that supports or contradicts the process.
Identified dissolution process
Polymer
Factors affecting
Polarity,
attraction
forces between them.
Rule that supports the process
Sodium Hydroxide and water
All hydroxides are insoluble
except those of the Group 1
elements, Ba(OH)2, and
Sr(OH)2. Ca(OH)2 is slightly
soluble.
Hydrogen Chloride and water
All chlorides are soluble except
AgCl, Hg2Cl2, and PbCl2
This is a group work. Make sure that both of you contributes in the completion of this
activity. Write all you answer to the big question and the small questions on the same
sheet of paper and submit to your subject teacher at the end of the period. Or email to
your subject teacher :
etaqued@yahoo.com.ph