Introduction to Chemistry Labs: Aqueous reactions
Overview
Laboratory Manual of Introduction to Chemistry
Equeous Reactions
Aqueous Reactions
Please watch the video of this experiment
Many chemical reactions occur in an aqueous solution. A solution is a homogeneous mixture of a solute dissolved in a solvent. Solutions may involve gases (such as air), liquids (e.g., blood), or even solids (steel). We will usually deal with aqueous solutions in which water is the solvent.
Solutions allow chemical and biological reactions to happen quickly by providing the medium that brings reactants to close together so they can rearrange and reform. Solutions are also the means by which substances can be transported from one place to another. Liquid solutions are particularly important in geological, environmental, biological, and chemical systems; the universal solvent for these solutions is water. The extent to which these processes occur is determined by the relative strengths of the solute-solute, solute-water, and water-water interactions.
Chemical reactions in aqueous solution may be divided into four major types: precipitation, acid-base, oxidation-reduction, and complexation. This lab will focus on precipitation reactions, in which an insoluble compound is produced from the aqueous reactant solutions.
In Part I, two representative substances (Kl and Pb(N03)2 will be used to investigate the solution properties, the principle of solubility, and the reaction properties of aqueous solutions.
In Part II, a variety of precipitation reactions will be performed by combining aqueous solutions of ionic compounds in pairs, and the reactions that occur will be analyzed and described.
Part I: Why Use Solutions for Reactions?
- Use a spatula to place a small number of Kl crystals on a clean, dry laptop.
Use a (different) spatula to place a few crystals of Pb(N03)2 about 1 cm away from the Kl crystals.
- Push the crystals of Kl and Pb(N03)2 together and gently stir to mix. Record your observations.
- How well do solid Kl and Pb(N03)2 react in the absence of water? Explain
- Add a few drops of H20 to the KI/Pb(N03)2. Gently stir to mix. Record your observations.
- How well do solid Kl and Pb(N03)2 react in the presence of water? Explain
- A pipette makes a pool of water about 5 cm in diameter on the laptop.
Carefully place a few Pb(N03)2 crystals near, but not in, one side of the pool.
Place a few crystals of Kl near, but not in, the other
side of the pool.
- Gently push the Pb(N03)2 crystals into their edge of the pool, and then push the Kl crystals into the other edge. Record your observations.
- Briefly but completely explain the chemistry of what was observed.
- Would it matter if the Kl had been added to the water first and the Pb(N03)2 seconds?
- Based on your results from this investigation, briefly explain why it is important to use solutions to carry out chemical reactions of this type.
Part II: A Bunch o' Chemical Reactions in Aqueous Solutions
- Start with the laptop surface's upper left box in the Reaction Grid. Place 1 drop of Pb(N03)2 solution in the middle of the box, then carefully add one drop of Kl solution.
Describe the appearance of each of the initial solutions before mixing. Then, observe and record any visible changes (such as a color change, formation of a precipitate, the evolution of a gas, etc.) that you observe.
Note: The Grid background is both white and black. Color changes are more easily seen on a white background. The precipitate formation can be seen better on the black background. Please complete the following table:
Observation Table:
Please write your observation of the reaction of every two reagents in the cross square.
Column1Column2Column3Column4Column5Column6Column7Column8
| |||||||
KI | NaCl | Na2SO4 | Na3PO4 | NaC2H3O | Na2CO3 | NaOH | |
Pb(NO3)2 | |||||||
AgNO3 | |||||||
CaCl2 | |||||||
CuCl2 | |||||||
FeNO3 | |||||||
- Repeat this procedure in the top row of the following box, but this time, combine one drop of NaCl with one drop of Pb(N03)2.
- Continue this binary-mixing process in all the other boxes, using the appropriate aqueous solutions indicated on the Reaction Grid. Record your initial and final.
Important Note: Avoid cross-contamination between the pipettes and the solutions on the laptop since this will severely affect your results.
- If you doubt the results of any (possible) reaction, repeat it. If appropriate, add more drops of either substance, stir again, Feel free to explore to your heart's content!
- When done, clean the laptop surface and dispose of the mixtures. Wash your hands with.
Extra Points assignment:
Please watch this video about the Net ionic equation and spectator Ions
Analysis
For each of the following combinations:
|
c) Indicate whether a precipitation reaction has occurred (or not).
d)Identify all spectator ions and state the name of the solid.
1) Reaction of solution of lead(II) nitrate with solution of potassium iodide
2) Reaction of solution of sodium chloride with solution of silver nitrate
3) Reaction of solution of Calcium chloride with solution of sodium sulfate
4) Reaction of solution of silver nitrate with solution of sodium phosphate
5) Reaction of calcium chloride with the solution of sodium phosphate
6) Reaction of solution of sodium acetate with the solution of lead nitrate
7) Reaction of solution of sodium chloride with solution of copper(II) chloride
8) Reaction of solution of Iron(IIi) nitrate with solution of sodium chloride
Your summary of the procedure:
Observations made during the Lab:
List all chemical equations used in the lab:
List all calculations used in the lab:
Answers to any questions posed in the lab:
The results/conclusion of the lab:
Discussion (This section should be very brief and should include conclusions, and the student discusses what can be done in future experiments to prevent any errors and improve results.):
Thanks to Mark Blaser, Shasta College, for the original experimental procedure.