Lab 4: Types of Reactions
Objectives:
1. Observe changes in chemical and physical properties during a variety of chemical reactions
2. Write balanced chemical equations for all reactions carried out
3. Identify type of reaction carried out (some may be more than one type)
Background:
A chemical reaction consists of reactants and products. The reactants are what you start with (also called starting materials) and the products are the new compounds that form during the reaction. From section 5.3 of your text chemical reactions can be classified into three general categories: (1) Combination (2) Decomposition and (3) Displacement (single and double). These reaction types can be represented by generic chemical equations as follows:
Combination: A + B ® AB
Decomposition: AB ® A + B
Single-displacement: A + BC ® AC + B
Double-displacement: AB + CD ® AD + CB
Within the above categories, reactions can be further categorized as precipitation or re-dox reactions. During a precipitation reaction, an insoluble solid (precipitate) is formed as a product. A re-dox reaction occurs when electrons are exchanged between the reactants. In addition, reactions can be classified as exothermic (releasing heat) or endothermic (consuming heat). In this lab you will carry out various reactions and make careful observations about what you see. In the data report you will express them as balanced chemical equations and determine what type of reaction has taken place.
Pre-Lab (to be answered in lab notebook):
1. What type of reaction do you expect each to be?
2. Compare reaction 7 to reaction 8. Are they the same reaction in different directions? How can you tell?
Safety Notes:
· Wear your safety goggles at all times
· Handle all chemicals carefully (rinse them off your skin immediately)
· Take only the amount of chemicals that you need and never put unused chemicals back into the reagent bottle
· Discard all used or leftover chemicals in the waste containers provided (do not pour any chemicals down the sink and do not put your rinse water in the waste)
· Clean up any spills immediately and clean up everything when finished
Procedures:
Carry out the following reactions. For each reaction, carefully write down all observations (color change, gas evolution, formation of a precipitate, or temperature change) below the appropriate reaction on the pages you created for the pre-lab. Your observations will be turned in and graded along with the data sheet.
Use clean test tubes for the reactions.
Reaction #1 Mg + O2 à MgO
Procedure: Clean a Mg strip with glass or steel wool. Using tongs to hold the Mg strip, burn the strip. Dispose the product in the solid waste container.
Reaction #2 NH4OH(aq) à NH3(g) + H2O
Procedure: Open the bottle of conc. NH4OH. Test the pH of the fumes using a wet piece of pH paper. Do not touch the sides of the container.
Reaction #3 Mg + HCl (aq) à H2 (gas) + Mg2+(aq) + Cl-(aq) .
Procedure: Place a strip of Mg in 1 mL of 0.1M HCl.
Reaction #4 AgNO3(aq) + HCl (aq) à AgCl(s) + HNO3 (aq)
Procedure: Mix 0.1M HCl with 0.1M AgNO3 in equal volumes.
Reaction #5 HCl(aq) + NaOH(aq) à H2O + NaCl(aq)
Procedure: Measure the pH of 0.1M HCl and 0.1M NaOH. Mix the two in equal volume and stir well. Measure the pH of this mixture. Did the reaction generate heat?
Reaction #6 CO32- + H+ à H2CO3 à H2O + CO2 (gas)
Procedure: Place CaCO3 (s) in 2 mL of 0.1M HCl.
Reaction #7 Cu + ZnSO4(aq) à CuSO4(aq) + Zn
Procedure: Place a small piece of Cu (s) in 1 mL of 0.1 M ZnSO4.
Reaction #8 Zn + CuSO4(aq) à Cu + ZnSO4(aq)
Procedure: Place a small piece of Zn (s) in 1 mL of 0.1M CuSO4.
Data: For each reaction write the balanced chemical equation. List all types of reaction that apply (1) Combination (2) Decomposition (3) Displacement (single and double). Also include precipitation, oxidation-reduction and exothermic/endothemermic if detected.
Post Lab Questions:
1. In reaction #4, what was the solid that formed in the reaction?
2. In reaction #3, what were the bubbles in the solution?
3. Did the reaction types match your predictions?
4. Where you surprised by the results of reactions 7 and 8? Why do these results make sense? Hint reactions generally proceed from high energy to low energy like a boulder rolling down a hill.