For today’s lab, we are going to build on some of the information about classifying chemical reactions we learned last week.
Reading: The Home Scientist Lab Manual Topic III-4. Observe Double Replacement Reactions p.77-82,
Experimental Title: Lab 10: Double Displacement Reactions
Date of laboratory: August 5, 2014
Purpose: The purpose of this laboratory is to observe a series of double displacement reactions.
Read the background to the experiment on page 77-78.
It is a bit confusing, but chemists use the terms “double-replacement” and “double displacement” interchangeably, and this type of reaction may also be called a “metathesis” reaction. Extra credit to anyone who can find out which term is better to use or if one term is “displacing” the other. For our class, I will accept all these terms, but I will follow the textbook and call it double displacement in my own writing.
A double displacement reaction involves two compounds switching ions. If A and B are cations and X and Y are anions, then the reaction is AX + BY -> AY + BX.
In this lab session, we will test dilute solutions of the following eight cations:
□ Barium(II) or Ba2+ (from barium nitrate solution)
□ Calcium(II) or Ca2+ (from calcium nitrate solution)
□ Copper(II) or Cu2+ (from copper(II) sulfate solution)
□ Hydrogen or H+ (from hydrochloric acid solution)
□ Iron(II) or Fe2+ (from iron(II) sulfate solution)
□ Iron(III) or Fe3+ (from iron(III) chloride solution)
□ Lead(II) or Pb2+ (from lead(II) acetate solution)
□ Magnesium or Mg2+ (from magnesium sulfate solution)
against the following twelve anions:
□ Bromide or Br- (from potassium bromide solution)
□ Carbonate or CO32- (from sodium carbonate solution)
□ Chloride or Cl- (from hydrochloric acid solution)
□ Dichromate or Cr2O72- (from potassium dichromate solution)
□ Ferricyanide or [Fe(CN)6]3- (from potassium ferricyanide solution)
□ Ferrocyanide or [Fe(CN)6]4- (from sodium ferrocyanide solution)
□ Hydroxide or OH- (from sodium hydroxide solution)
□ Iodide or I- (from potassium iodide solution)
□ Oxalate or C2O42- (from oxalic acid solution)
□ Phosphate or PO43- (from phosphoric acid solution)
□ Sulfate or SO42- (from magnesium sulfate solution)
□ Sulfide or S2- (from sodium sulfide solution)
to determine if a reaction occurs.
If you have time, do some research and see if you can make some predictions as to what might happen in each of the pairings.
Special safety concerns for Lab 10:
This week we have to take lab safety very seriously. We are only doing this lab because you have shown you can be responsible up to now. Keep up the good work.
- Important: Be sure to wear gloves and goggles for the entire lab this week. Also, please wear long pants and closed-toe shoes. No exceptions this week!
- We will be doing the experiments in trays this week. Keep all the chemicals in the trays, please.
- The most dangerous chemicals are : 6M hydrochloric acid and the 6M sodium hydroxide. Those are strong concentrations. Barium, lead and dichromate can also be toxic. Use extra caution with those chemicals.
- If an acid spills, especially the 6M hydrochloric acid, cover the area of the spill with baking soda immediately! If it on you, go wash in the sink. Notify your instructor.
- If a base spills, especially the 6.0 M Sodium hydroxide, please cover it immediately with acetic acid (vinegar). If it on you, go wash in the sink. Notify your instructor.
- If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
- Be sure to wash your hands very carefully when you are finished with this lab.
See the list page 77.
Write down the Procedure on pages 78-81 the lab manual. Be sure to leave room for the data table to record your results. It might be useful to underline, star, or otherwise note the 6M hydrochloric acid, 6M sodium hydroxide, barium, lead and dichromate whenever you work with them so you know those are chemicals to use with extra caution.
24-Well Reaction Plate:
Once you have completed the experiment and cleaned up, sit down and write a sentence or two to explain the results. It is always a good idea to do this part while the experiment is fresh in your mind.
Record any thoughts you have about the experiments, including:
- Possible improvements to the procedures or how to tweak techniques
- How the results differed from your expectations
- Whether the goals were met
- Suggestions for other experiments
- The answers to the review questions he provides on page 82.
Please leave a comment or send an e-mail if you have any questions before our meeting.