Lab 5: Solubility & Colligative Properties of Solutions
Objective
- Gain experience mixing and diluting solutions
- Learn about the effect of concentration on osmosis
- Predict precipitation reactions
Introduction
Part 1:
Solutions are composed of a solute (smaller amount in solution) dissolved
in a solvent (larger amount in solution). The concentration of the solution
communicates the relative amount of solute to solvent. Common measures of
concentration are % weight/volume (grams / milliliter x 100%) and Molarity
(moles / Liter):
% w/v = m (g) x 100%
V (mL)
Molarity (M) = n (moles)
V (Liters)
When diluting solutions to a new concentration more solvent is added, but
the amount of the solute remains the same. Because the number of moles of
solute does not change we can use the following equation to determine the new
concentration of the solution:
M1V1 = M2V2
Part 2:
In this lab we will study two properties of solutions: their colligative
properties and the solubility of different solutes. Colligative properties are not
dependent on the nature of the reactants, only the number of particles dissolved
in solution. A non-volatile, covalent molecule like glucose (C6H12O6) will dissolve
in water as one particle (or one mole of particles):
C6H12O6 (s) + H2O (l)  C6H12O6 (aq)
A non-volatile ionic compound like sodium chloride (NaCl) will dissolve into two
particles (or two moles of particles):
NaCl (s) + H2O (l)  Na+ (aq) + Cl- (aq)
As the number of particles in solution increase, there is a greater effect on
colligative properties like freezing point, melting point, and osmosis. Osmosis is
the process in which small molecules (like water) pass through a semi-permeable
membrane (like our cell walls) while preventing the passage ionic compounds
and large molecular weight compounds. Water will pass through the membrane
to dilute the side that has the higher concentration of particles.
Part 3:
Fluid therapy is commonly used in the medical field, it is the administration
of drugs through IV fluids. The solubility rules for ionic compounds can be used
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to predict the compatibility of different IV solutions. Some ionic compounds are
insoluble in water (see solubility rules in text, Chapter 8.3B), and if the separate
ions that make up these compounds are found in different drugs or IV solutions
and combined dangerous solids precipitate out of solution. IV solutions can also
be incompatible if a chemical reaction occurs that changes the chemical structure
of a drug (this is often acid/base reactions), or if the drugs solubility decreases
with the increase in water concentration. More information about IV solution
compatibility can be found in the following article:
http://www.medscape.com/viewarticle/590261_6
Pre Lab Assignment: (must be completed before starting lab)
 Name, date, title of lab
 One to two sentences stating the objective of this lab
 Summary of lab procedure (brief paragraph in your own words)
 Answers to pre-lab Questions:
1. If a stock solution is 5 M and you need to prepare a solution that
will be 1 M and have a volume of 5 mL, what volume of the stock
solution do you need to measure out dilute with water to 5 mL?
2. Define isotonic, hypotonic, and hypertonic.
3. Consider the ionic compounds that you will be studying in Part 3:
NaHCO3, CaCl2, and MgSO4. Write a chemical equation for the 3
combinations that will be performed in part 3. In each case identify
if any of the products will precipitate out of solution. (Hint: use the
solubility rules outlined in your textbook pg 271)
Notes
Experimental set up for part 2 is demonstrated below. You will use dialysis tubing
to create a bag that contains a known concentration of a solution that will be
placed in a solution with an unknown concentration of particles.
.
Procedure
Part 1: Prepare a Stock Solution of SOLUTE
1. Using a 100 mL graduated cylinder measure about 70 mL of DI water.
Record the exact volume using the correct number of sig figs.
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2. Prepare a stock solution by first weighing out 10.227g of NaCl using
weighing paper, and recording its exact mass. Then mix the NaCl with the
70 mL of DI water from step 1 in a beaker and stir until dissolved.
3. Measure the volume of the solution by pouring the solution back into the
graduated cylinder (be careful not to spill), again record the correct
number of sig figs.
4. Calculate the concentration of your stock solution as % w/v and Molarity.
Part 2: Concentration & Colligative Properties
1. Label 3 150 mL beakers #1-#3.
2. Using a 10 mL syringe measure 6.1 mL of stock solution from part 1 and
add it to beaker #1.
3. Using a graduated cylinder add 94 mL of DI water to beaker #1 and stir.
4. Using a graduated cylinder measure 61 mL of stock solution and 39 mL of
DI water and them to beaker #2.
5. Add 100 mL of DI water to beaker #3.
6. Calculate the concentrations of beakers #1 and #2. (this can be done after
lab)
7. Make three “cells” using dialysis tubing and the provided saline solution
with an unknown concentration:
a. Obtain 3 sections of dialysis tubing and soak for 5 minutes in DI
water (use a large beaker).
b. Tie a knot at one end of each piece of tubing after soaking.
c. Using a syringe add 10.0 mL of unknown solution into each bag,
eliminate any large air bubbles1, then tie tubing closed. (see notes
for an example)
d. Rinse the filled bags with DI water by dipping in a beaker of DI
water (not beaker #3) and then gently blot off the excess water with
a paper towel.
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8. Weigh and record the mass of the bag in the column marked initial mass.
9. Add a bag to each of the beakers (#1-#3). Be careful to keep track of
which bag is in which beaker.
10. After at least 30 minutes (continue to part 3 of the lab while you wait)
remove each bag from its beaker, blot off the excess fluid and weigh the
bag. Record the mass in the column marked final mass. Note: try to blot
the bags in the same way you did for the initial mass.
11. After the experiment cut open the bags and dispose of the contents in the
hazardous waste.
Part 3: Solubility
1. Obtain 3 test tubes 0.25 M NaHCO3, 0.25 M CaCl2, and 0.25 M MgSO4
2. Combine about 3 mL of NaHCO3 with 3 mL of CaCl2 in a test tube.
Record observations about any physical changes that occur.
3. Repeat step 2 in a fresh test tube for each combination of the 3
reagents, filling in the data table with your observations.
4. Wait at least 5 minutes and record observations again. Are their any
changes in the solution’s appearances?
5. Dispose of reaction mixtures in the hazardous waste.
6. Class observations will be collected, please add your results to the
chart on the white board.
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Lab 5: Data & Observation Worksheet
Part 1: Preparing Stock Solution of SOLUTE
Volume of DI Water __________________
Mass of SOLUTE ____________________
Concentration of Stock Solution:
%w/v __________________
Calculation:
Molarity __________________
Calculation:
Observations:
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Part 2: Concentration & Colligative Properties
Sample
Volume Stock
Solution
Volume DI Water
Beaker 1
Beaker 2
Beaker 3
Concentration
Solution
(Molarity)
Initial Mass
Dialysis “bag” with
Solution
Final Mass
Dialysis “bag” with
Solution
Mass Lost (-) or
Gained (+)
Isotonic,
Hypertonic, or
Hypotonic?
Observations:
Sample Calculations: (provide a sample for each type of calculation performed)
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Part 3: Solubility
NaHCO3
+ CaCl2
NaHCO3
+ MgSO4
MgSO4
+ CaCl2
Immediate
Observations
Observations
After 5 min.
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Lab 5: Post-lab Report
 Results: Fill out Data & Observations worksheet legibly.
o Use correct significant figures
o Show a sample calculation for each calculation performed.
 Error Analysis Discussion: One of your solutions should be isotonic with
the unknown solution. Identify the isotonic solution, and provide evidence
for this assignment. If none of your solutions is isotonic discuss possible
sources of error, please be specific (“human error” is not an acceptable
answer). If one of your solutions is isotonic, or close to isotonic discuss
any errors or aspects of the procedure that account for small differences in
concentration between the unknown and the solution you made, again
please be specific.
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 Post-Lab Questions:
1. Assume the stock solution in part 2 was the same concentration but
a solution of Na3PO4 dissolved in water rather then NaCl. What
would be the concentration of particles in beakers #1 and #2?
Would you expect any differences in your results (ie, assigning
hypertonic, hypotonic, and isotonic)?
2. The solutions in Part 3 are all IV solutions used in fluid therapy.
Which combination of solutions would be incompatible with each
other and need to be administered separately? How does this
compare with your predictions from pre-lab question 3?
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