Reactions of Ions
Introduction:
Ionic compounds are made up of positively and negatively charged particles. In a water
solution, these compounds dissociate, or break up into the ions of which they are made.
For example, in water, solid sodium nitrate, NaNO3 , breaks up into separate Na+ and
NO3- ions; sodium carbonate, Na2 CO3 , breaks up into Na + and CO3 2- ions; and calcium
nitrate, Ca(NO3 )2 , breaks up into Ca 2+ and NO3 - ions. When two ionic compounds are
present in dissociated form in the same solution, different compounds may form. For a
different compound to form, a chemical reaction must occur. A change in the appearance
of the solution indicates that a chemical reaction has taken place.
Problem:
How can you determine which ionic compound has formed in a solution containing
known ions?
Materials:
graduated cylinder
sodium nitrate solution
sodium carbonate solution
4 droppers
test tube rack
grease pencil
white vinegar
4 test tubes
stoppers for test tube
calcium nitrate solution
Procedure:
1. On your table you will find the following chemicals:
Sodium nitrate
Calcium nitrate
Sodium carbonate
Vinegar (acetic acid)
2. Observe the appearance of each solution and record your observations in
your data table.
3. Add a dropper-full of sodium carbonate solution to one of the test
tubes.
4. To the same test tube, add a dropper full of calcium nitrate solution.
Observe what happens and record in a data table. Do not throw away
the contents of this test tube because it will be used again in the
experiment.
5. To a clean test tube, add a dropper full of sodium nitrate solution.
6. Add a dropper full of vinegar to the sodium nitrate solution. Stopper
the test tube and shake gently. Observe what happens and record in
your data table.
7. Add a dropper full of vinegar to the first test tube that contained the
calcium nitrate and sodium carbonate solutions. Tap the test tube
gently to mix the contents. Observe what happens and record the
information in your data table.
Observations:
Solution
Sodium carbonate
Calcium nitrate
Sodium nitrate
Vinegar (acetic acid)
Observation of appearance
Reactants
Observations
Sodium carbonate +
calcium nitrate
Sodium nitrate +
acetic acid
Acetic acid + contents
of tube with sodium
carbonate and calcium
nitrate.
Analysis:
1.
a. What was the evidence that a chemical change occurred when the calcium
nitrate and sodium carbonate were mixed?
b. Based on your answer and your knowledge of ions in solution, what are
the possible compositions of the visible products that formed during this
reaction?
c. Based on your observation on what sodium nitrate looks like, what do you
think was the actual product of this reaction?
d. Based on your previous answer, what ions remained in solution?
2. What do you think was formed when acetic acid was added to the test tube that
contained the products of the calcium nitrate and sodium carbonate mixture?
How did you come to this conclusion? Hint : Think about what happened
when you mixed the acetic acid and the sodium nitrate solution to help you
rule out possibilities.
3. What do you think would happen if you mixed acetic acid and sodium carbonate?
Conclusion:
1. Write a sentence or an equation to explain what happened when calcium nitrate
was added to sodium carbonate.
2.
a. Do reactions involving ionic substances affect all the particles in solution,
or do some ions not react? Explain your answer.
b. Why are some particles called spectator ions?
3. Using the information from the lab, make a general statement about what can
happen when solutions containing different ions are mixed.