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Name______Date______Period______
Reactions in Solution: Precipitation
Problem: What sort of driving forces cause reactions to occur in aqueous solution?
Introduction: This is a simple experiment that will introduce you to the concept of driving forces. By driving forces, we mean the reactions occur. One of the chemist’s most intriguing problems is to understand why things happen as they do. In addition, this experiment will give you some added practice in recognizing and writing equation for precipitation (double replacement) reactions.
You will be given six solutions, all are labeled “0.2 M”; this refers to the concentration of solution. You are to test the solutions in pairs, looking for evidence of reaction in the form of a color change or formation of a precipitate. Some of the pairs will react; many will not. For those that do, write balanced equation, you will also be expected to identify, by name and formula, the precipitate in each case.
Prelaboratory Assignment: Read the Introduction and Procedure before you begin. Answer the Prelaboratory Questions. (Refer to p.109 Table 4.4 for naming compounds and Table 8.1 (p.245) and notebook p. 28 Precipitation Diagram for solubility)
I. Write the formula for the following ionic compounds.
a. zinc sulfide ______b. chromium (II) hydroxide ______
c. lead (II) phosphate ______d. iron (III) bromide ______
2. Write chemical equation for the following ionic compounds (electrolytes) dissolving in water. For example, potassium chloride: KCl (s) (water) → K+ (aq) + Cl- (aq)
a. sodium chloride
b. copper (II) chloride
c. iron (III) sulfate
3. Write a molecular equation for the reaction that occurs when a solution of cobalt (II) nitrate reacts with aqueous potassium phosphate, producing a precipitate of cobalt (II) phosphate and aqueous potassium nitrate.
4. All of the reagent solution have a concentration of 0.2 M. This means that there is 0.2 mole of dissolved substance per liter of solution. What will be the concentration after mixing, assuming you use equal volume of each solution?
5. How will you recognize formation of a small amount of insoluble solid?
Data Table (Rx = Reaction)
Group B → / CoCl2 / AlCl3 / NiCl2Group A ↓
NaI / Rx #1 / Rx#2 / Rx#3
Na2CO3 / Rx#4 / Rx#5 / Rx#6
NaOH / Rx#7 / Rx#8 / Rx#9
Analysis and conclusions (Refer to Table 8.1 (p.245) for solubility)
For those combinations in which the formation of a precipitate was observed, do each of the following:
a. Write the name and formula of the precipitate. (If there is no PRECIPIATE, write NONE)
b. Write a balanced molecular equation for the reaction that took place.
c. Write a balanced “complete ionic equation”
d. Write a balanced “net ionic equation”, showing all dissolved species as ions, and all precipitate as molecules. (If there is no precipitate forming, write NO NET IONIC EQUATION)
Rx (Reaction) #1 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 2 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 3 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 4 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 5 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 6 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 7 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 8 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation
Rx # 9 a. Name and formula of precipitate
b. Molecular equation
c. Complete ionic equation
d. Net ionic equation