Reactions between Aqueous Solutions of Ionic Compounds, Acids, Bases and pH
Introduction:
Most biological systems contain vast amount of water. For example, human body
consists from 50-75% water by mass depending on age, hydration level and many other
factors. Many biochemical reactions that are crucial for the proper function of biological
systems occur in water. Understanding chemical reactions in aqueous solutions is critical
in comprehending how biological systems function.
When ionic compounds become soluble in water, ions are solvated by water
molecules via ionic-dipole interactions. Here’s the link to an online animation of table
salt dissolving in water:
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf Keep in
mind, not all ionic compounds are soluble in water. Here’s the link to a Wikipedia page
that explains solubility in detail: http://en.wikipedia.org/wiki/Solubility_rule Pay close
attention to the “Solubility of Ionic Compounds in Water” section.
In two aqueous solutions, there are two sets of ions that are solvated by water
molecules and moving freely. When mixed together, those solvated ions will collide with
each other. Certain collisions will produce compounds that are not or weakly soluble in
water according to the Solubility Rules. Hence aqueous solutions of ionic compounds,
acids, and bases may react to form precipitates, gas, or liquid water.
Acids and bases are unique class of chemicals since they are integral part of the
food people consume. pH scale was developed to measure the strength of acids and bases.
Read the Pearson online textbook Section 19.1 (only for the Arrhenius Acids and Bases)
and Section 19.2 (concept of pH and pOH, calculations of pH and pOH, and
measurements of pH) for background information on the topic.
Purpose:
The student will investigate reactions between aqueous solutions of ionic
compounds, acids and bases.
Materials / Equipment:
Sodium chloride solution
Sodium sulfate solution
Sodium carbonate solution
Calcium chloride solution
Silver nitrate solution
Barium chloride solution
Hydrochloric acid solution
Sodium hydroxide solution
Phenolphthalein indicator solution
Glass rods
Wash bottle
pH paper
Safety:
 Always wear safety glasses and apron in the chemistry lab.
 Never eat or drink in the chemistry lab.
 Avoid contact of all chemicals with eyes and all body tissues.
 Always dispose waste chemicals according to approved practices.
Pre-lab questions:
 Draw a schematic illustration for dissolution of ionic compounds in water.
 What is an aqueous solution?
 What is the solute? What is the solvent?
 What is solvation process for aqueous systems?
 Write formula units for all compounds used in the lab.
 What are acids? What are bases?
 What is the definition of pH? pOH?
 What are acid/base indicators? How do they work?
 What is the phenolphthalein indicator?
 What is the pH scale?
 What is a double-replacement reaction? How is it different from a singlereplacement reaction?
Procedure:
Part A:
1. Use clean microplate for the reactions. Each well should be used for one reaction.
2. Use distilled water to wash each cell carefully.
3. In three wells, mix solutions of sodium chloride, barium chloride, and calcium
chloride in pairs. Sodium chloride + barium chloride; sodium chloride and
calcium chloride; barium chloride and calcium chloride.
4. Record observations.
Part B:
1. Select a row of three wells. In each well, transfer 1/3-well full of sodium chloride
solution.
2. Select another row of three wells. In each well, transfer 1/3-well full of barium
chloride solution.
3. Select another row of three wells. In each well, transfer 1/3-well full of calcium
chloride solution.
4. Put 10 drops of sodium carbonate solution into the first column of wells spanning
sodium chloride solution, barium chloride solution, and calcium chloride solution,
respectively. Observe.
5. Put 10 drops of sodium sulfate solution into the second column of wells spanning
sodium chloride solution, barium chloride solution, and calcium chloride solution,
respectively. Observe.
6. Put 10 drops of silver nitrate solution into the third column of wells spanning
sodium chloride solution, barium chloride solution, and calcium chloride solution,
respectively. Observe.
7. Carefully record observations in data tables.
8. Dispose the contents according to instruction by the teacher.
9. Wash the microplate thoroughly first with tap water, then rinse 3 times with
distilled water.
Part C:
1. Transfer ~2 mL of sodium carbonate solution into a clean test tube.
2. Put in 10 drops of hydrochloric acid solution. Observe.
3. Dispose the contents according to instruction by the teacher.
4. Wash the test tube thoroughly with tap water.
Part D:
1. Transfer ~2 mL of hydrochloric acid solution into a clean test tube.
2. Put in 2 drops of phenolphthalein indicator.
3. Dip a clean glass rod into the solution. Transfer a drop or two of the solution onto
a piece of fresh pH paper. Let the color on the pH paper fully develop. The
process generally takes less than 10 seconds. Compare the
4. Introduce sodium hydroxide solution into the test tube drop by drop.
5. For every 20 drops of sodium hydroxide solution, shake the test tube and observe.
Repeat Step 3. Note: each time after pH testing, rinse the glass rod thoroughly
with distilled water before next measurement.
6. Repeat Steps 3-5 until pH value reaches 12 or above.
7. Dispose the contents according to instruction by the teacher.
8. Wash the test tube thoroughly with tap water.
Data Analysis:
 Carefully process all observations.
 Attempt to find trends in the data sets.
Post-lab Questions:
1. For Part A, write possible outcomes for the double-replacement reactions. Are
there any chemical changes? What do the observation mean regards to solubility
of those ionic compounds containing chloride?
2. For Par B, write possible outcomes for the double-replacement reactions. Are
there any chemical changes? Summarize solubility of ionic compounds involved
in those mixtures.
3. Postulate what happened on the microscopic scale for Part C.
4. Postulate what happened on the microscopic scale for Part D.
5. What are Solubility Rules?
6. Do the data collected in this lab support the Solubility Rules? Explain.