Module 11

Define solubility
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent. It is usually expressed in grams of solute per 100 grams of solvent.
How does a solid solute dissolve in liquid solvents
The solvent molecules of a solid must be attracted to the solute molecules so strongly that the solvent molecules can get between the solute molecules (or ions) and pull them apart from each other.
How does a liquid solute dissolve in liquid solvents
The solvent molecules of a liquid need only be attracted to the solute molecules a little because the solvent does not need to separate the solute molecules very much. The solvent merely needs to get between the solute molecules.
How does a gas solute dissolve in liquid solvents?
The solvent molecules of a gas must be attracted to the solute molecules enough to pull the solute molecules closer to one another.
What is a exothermic process?
A process that RELEASES heat.
What is an endothermic process?
A process that ABSORBS heat.
In lab, you and your partner contaminate your solution with a gas. What can you and your partner do to get rid of the majority of this dissolved contaminate?
Heat up your solution, this will drive the gas out of the solution.

Tue or False:

 

Solids usually increase in solubility with increasing temperature

True
Memorize the equation for freezing-point depression

ΔT = -i·Kf·m

 

ΔT : change in temp

 

i: the number of molecules (or ions) that the solute splits into when it dissolves

 

Kf : freezing point constant

 

Study 11.3 to know how to solve these equations

 

How can you tell which of these 2 solutes will raise the boiling point of a liquid the most?

 

 

NaCl or Na2CO3

The solute that will raise the boiling point the most is the one that splits into the most ions when dissolved.

 

So Na2CO3 would be the answer since it will split into more ions than NaCl

Know the difference between molarity and molality

Molarity: the number of moles of solute PER LITER OF SOLUTION

 

 

 

Molality: the number of moles of solute PER KILOGRAM OF SOLVENT

Study the stoichiometry in this module.

 

Here is an example problem:

 

The following reaction was performed in the lab:

 

3K2CO3 (aq) + 2Al(NO3)3 (aq) —> Al2(CO3)3 (s) + 6KNO3 (aq)

 

If 191 ml of 1.25 M aluminum nitrate is added to an excess of potassium carbonate, how many grams of aluminum carbonate will be produced?

 

 

This is just a stoichiometry problem. We can tell this by the fact we are being asked to determine the amount of one substance when we are given the amount of another substance. The only way to do that is by stoichometry. Now, in order to do stoichiometry, we must first get the amount in moles:

 

1.25 moles Al(NO3)3   

            1L                 x   0.191L + 0.239 moles Al(NO3)3

 

 

Now we have moles, we can do stoichiometry:

 

0.239 molesAl(NO3)3         1 mole Al2(CO3)3

          1                    x    2 molesAl(NO3)

 

 

= 0.120moles Al2(CO3)3

 

Now of course, this is not quite the answer we need. We were asked to figure out how many grams of aluminum carbonate were produced, so we have to convert from moles to grams.

 

0.120 moles Al2(CO3)3         234 grams Al2(CO3)3 

            1                   x       2 moles Al2(CO3)3

 

 

Final Answer =  28.1 grams Al2(CO3)

 

Know this equation:

 

Molality m= #moles solute

                 # kg solvent

 

Example problem: What is the molality of of a solution made from 2.84 moles of PO4 and 4.44 kg of water?

Molality m= #moles solute            2.84 moles of PO4

                  # kg solvent      =             4.44 kg          =

 

 

0.63 moles

         kg         = .063 m final answer

x

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