Metathesis reactions lab

Experiment 4 Inorganic Compounds

and Metathesis Reactions

• To characterize the physical appearance of common laboratory chemicals

• To systematically observe and express the stages of a metathesis reaction • To determine the solubilities of some salts by studying metathesis reactions

The following techniques are used in the Experimental Procedure

By now you have learned to name and write the formulas for a large number of inor-

ganic compounds. In addition you should also be familiar with balanced equations and

stoichiometry. But names, formulas, and equations have little meaning unless there is some tangible relationship to chemicals and chemical reactions. To a chemist, sulfur is

not just an element with the symbol S that reacts with oxygen to form sulfur dioxide,

but rather a yellow solid that can be held in the hand and burns in air with a blue flame,

producing a choking irritant called sulfur dioxide.

In this experiment you will “look” at some laboratory chemicals with the intent

that a mental association develops between a compound’s formula and its physical ap-

pearance. You will also conduct a number of chemical reactions, observe some of the

chemical properties of chemicals, and make conclusions on the basis of your observa-

tions.

In Part A, a number of compounds are identified by their formulas, names, physi-

cal states, colors, crystal characteristics (if a solid), and solubilities in water.

In Part B, the chemical reactions of some ionic compounds are studied in an aque-

ous solution. In these chemical reactions two ionic compounds, as reactants, are dis-

solved in solution whereby the ions are free to exchange partners to form products. A

chemical reaction (an exchange of ionic partners) is observed if a chemical change is

evident, such as the formation of a precipitate or the evolution of a gas. These chemical

reactions are called metathesis (or double displacement) reactions. To systematically interpret the progress of a metathesis reaction, a sequence of ob-

servations and equation writing steps are followed. Using the salts silver nitrate and sodium chloride as reactants, these steps are as follows:

1. Define the Reactants. Write the formulas of the reactants.

AgNO3 )1.4(lCaN

Experiment 4 81

Metathesis reaction: the interchange of ions between two compounds involved in a reaction

Objectives

Drops of a potassium hydroxide solution added to an iron(III) chloride solution produces insoluble iron(III) hydroxide.

Techniques

Introduction

2 4 7a 7b 17a 17b

Stoichiometry: a study of a chemical reaction using a balanced equation

Salt: an ionic compound

82 Inorganic Compounds and Metathesis Reactions

Figure 4.1 The progression of a reaction between solutions of silver nitrate and sodium chloride.

2. Determine the Products and Write the Molecular Equation. The formulas of the products are written by exchanging the cations with the anions of the reactants.

A balanced molecular equation for the proposed metathesis reaction is

AgNO3 NaCl l AgCl NaNO3 (4.2)

It is this molecular equation that is studied in detail in the laboratory—what is the

nature of each of these substances in aqueous solution?

3. Formulas of Reactants in Solution. The physical states of the reactants in so- lution before mixing are observed; for example, are the salts soluble or insoluble?

What is their actual appearance? The formulas of the salts are written accordingly, ei-

ther as separated hydrated ions or as a solid.

Both silver nitrate and sodium chloride are soluble salts (Figure 4.1a). The cations

and anions of the two salts move about the aqueous solution as separate hydrated

species; each is written as (aq).

Ag (aq) NO3 (aq) Na (aq) Cl (aq) l (4.3)

4. Evidence of Reaction. On combination of the ions from the two aqueous solu- tions into a single system, an observation determines whether or not a reaction has oc-

curred between the ions. A chemical reaction is observed when

• a precipitate forms

• a gas is evolved

• heat is evolved or absorbed

• a color change occurs

• a change in acidity (or basicity) occurs

• light is emitted

In this system, the formation of the white precipitate of silver chloride is observed

(Figure 4.1b).

5. Formulas of Products in Solution. The formulas of the products are then written as they appear in the aqueous solution after the mixing (Figure 4.1c). A pre-

cipitate is written as (s), and an ion remaining in solution is written as (aq).

l AgCl(s) Na (aq) NO3 (aq) (4.4)

6. Ionic Equation. The reactants (from Step 3) and the products (from Step 5) are combined to form a balanced ionic equation that represents each species as it actually exists in the aqueous solution.

Ag (aq) NO3 (aq) Na (aq) Cl (aq) l

AgCl(s) Na (aq) NO3 (aq) (4.5)

7. Net Ionic Equation. A final equation, called the net ionic equation, includes only those ions responsible for the observed reaction. The ions present, but not involved

in the observed reaction, are considered spectator ions and do not appear in a net ionic equation. The sodium and nitrate ions are not involved in any observable reaction.

Ag (aq) Cl (aq) l AgCl(s) (4.6)

Similar molecular equations, ionic equations, and net ionic equations are written

for a number of chemical systems in Part B of this experiment.

Procedure Overview: An array of laboratory chemicals are observed and de- scribed. Eleven metathesis reactions are observed, and appropriate formulas and

equations are systematically written to express the nature of each species in solu-

tion.

A broad selection of chemical compounds in test tubes or laboratory dishes (Figure

4.2) are located on the display table. Describe the color and crystal characteristics (if a solid) of each chemical; also predict the water solubility1 of each chemical. Use

the Report Sheet as a format for reporting your observations and predictions.

Attempt to group some of the compounds on the basis of color, crystal characteris-

tics, and/or solubility.

This experiment requires either a set of 12 clean, small test tubes or a 24-well plate.

Consult with your instructor. If you use test tubes, label them in accordance with the

well numbers in Table 4.1.

1. Test Solutions. Set up the test tubes (Figure 4.3) or the 24-well plate (Figure 4.4) with the reactant solutions or preparations listed in Table 4.1. Volumes of

solutions only need to be approximate.2 Your instructor may substitute, add, or

delete chemicals from the table.

2. Systematic Procedure for Studying Reactions. Pairs of reactant solutions are combined according to Figure 4.4. Record your stepwise analysis of each reac-

tion on the Report Sheet using the steps outlined in the Introduction. Be sure to

look for any evidence of a chemical change occurring.

Experiment 4 83

Spectator ions: ions that do not participate in an observable/detectable reaction

Experimental

Procedure

A. Identification

Figure 4.2 A view of the nature of substances.

1The predicted solubility is based on the rules in Appendix G. 2The volume of a small (75-mm) test tube is about 3 mL; the volume of each well is about 3.4 mL. 3Universal indicator is a mixture of acid–base indicators that gradually changes color, depending on the acidity of the solution.

B. Systematic Study of Metathesis Reactions

Crystal characteristics: shape (powder, granular, etc.), brightness, and wet or dry status

Table 4.1 An Organization of the Reactants for a Series of Metathesis Reactions

Test Tube No. or Well No. Reactant Solution or Preparation

OCaCfoslatsyrclareveS1A 3 0.3foLm22A M HCl and several drops of universal indicator3

0.3foLm23A M NaOH

lCeFfoslatsyrclareveS4A 3•6H2O in 2 mL of water or 2 mL of 0.1 M FeCl3 lCoCfoslatsyrclareveS5A 2•6H2O in 2 mL of water or 2 mL of 0.1 M CoCl2 ONgAfoslatsyrclareveS6A 3 in 2 mL of water or 2 mL of 0.1 M AgNO3

HNfoslatsyrclareveS3B 4Cl

aNfoslatsyrclareveS6B 2CO3 in 2 mL of water or 2 mL of 0.1 M Na2CO3 lCiNfoslatsyrclareveS4C 2•6H2O in 2 mL of water or 2 mL of 0.1 M NiCl2

aNfoslatsyrclareveS5C 3PO4•12H2O in 2 mL of water or 2 mL of 0.1 M Na3PO4 OSuCfoslatsyrclareveS6C 4•5H2O in 2 mL of water or 2 mL of 0.1 M CuSO4 lCaBfoslatsyrclareveS6D 2•2H2O in 2 mL of water or 2 mL of 0.1 M BaCl2

2

7a 7b

Use clean dropping pipets or Beral pipets to slowly make the following solu-

tion transfers:

a. Transfer approximately one-half of solution A2 to A1 in (test tube/well) A1.

b. Transfer one-third of solution A3 to the remainder of solution A2 in (test

tube/well) A2.

c. Transfer one-third of solution A3 to B3 in (test tube/well) B3. (Warm the test

tube in your hand or the bottom of the well with your finger and smell cau-

tiously. Test the fumes with wet, red litmus.)

d. Transfer one-half of solution A4 to the remainder of solution A3 in (test

tube/well) A3.

e. Transfer one-half of solution A5 to the remainder of solution A4 in (test

tube/well) A4.

f. Transfer one-half of solution A6 to the remainder of solution A5 in (test

tube/well) A5.

g. Transfer one-half of solution B6 to the remainder of solution A6 in (test

tube/well) A6.

h. Transfer one-third of solution C6 to the remainder of solution B6 in (test

tube/well) B6.

i. Transfer one-third of solution C6 to solution D6 in (test tube/well) D6.

j. Transfer one-half of solution C5 to the remainder of solution C6 in (test

tube/well) C6.

k. Transfer one-half of solution C4 to the remainder of solution C5 in (test

tube/well) C5.

3. Unknown Salt. To obtain an unknown salt, submit a clean, small test tube to your laboratory instructor. Using your acquired knowledge from Part B.2, identify the

cation and anion of the unknown.

CLEANUP: Rinse the test tubes or well plate with tap water twice and with deion- ized water twice. Discard each rinse in the sink, followed by a generous amount of tap

water.

84 Inorganic Compounds and Metathesis Reactions

A1 A2 A3 A4 A5 A6 B3 B6 C4 C5 C6 D6

1 2 3 4 5 6

A

B

C

D

CaCO3 HCl NaOH FeCl3 CoCl2 AgNO3

Na2CO3

CuSO4

BaCl2

NH4Cl

NiCl2 Na3PO4

Figure 4.3 The arrangement of 12 small, labeled test tubes for test solutions.

Figure 4.4 The arrangement of the test solutions in a 24-well plate.

17a 17b

Disposal: Dispose of the waste solutions, as identified by your instructor, in the “Waste Liquids” container.

2

4

Experiment 4 85

Date __________ Lab Sec. ______ Name ____________________________________________ Desk No. __________

1. a. Copper(II) sulfate dissolves in water to form a blue solution. What species are present in solution, i.e., what is actu-

ally swimming around in solution? Write the formulas.

b. Sodium carbonate dissolves in water to form a colorless solution. What species are present in solution? Write the

formulas.

c. When solutions of copper(II) sulfate and sodium carbonate are mixed, blue copper(II) carbonate precipitates. What

species remain in solution? (These are the spectator ions.) What is the color of the solution? [Assume that

stoichiometric amounts of copper(II) sulfate and sodium carbonate are mixed.] Write the formulas.

2. a. An aqueous solution of sodium hydroxide is labeled 0.010 M NaOH. What are the molar concentrations of NaOH,

Na , and OH in the aqueous solution? Explain.

b. An aqueous solution of calcium chloride is labeled 0.010 M CaCl2. What are the molar concentrations of CaCl2,

Ca2 , and Cl in the aqueous solution? Explain.

Experiment 4Prelaboratory Assignment

Inorganic Compounds and

Metathesis Reactions

3. Sodium phosphate dodecahydrate, Na3PO4•12H2O, is a crystalline salt that is water soluble. Describe what is present

in an aqueous solution of sodium phosphate dodecahydrate.

4. When aqueous solutions of ferrous sulfate and barium chloride are mixed, a white precipitate forms. With time the

aqueous solution turns a red-orange color.

*a. Refer to Appendix G. What is the white precipitate? Write the formula.

*b. Write a balanced equation using only those ions that are involved in the formation of the white precipitate (this is

a net ionic equation).

*c. Explain why the aqueous solution turns a red-orange color with time.

5. Write molecular equations for each of the following metathesis reactions:

a. AgNO3(aq) ZnI2(aq) l

b. CuSO4(aq) K3PO4(aq) l

c. K2CO3(aq) CaCl2(aq) l

d. Na2SO3(aq) HCl(aq) l

e. Ni(NO3)2(aq) K2C2O4(aq) l

6. List five observations, appealing to your senses, that indicate a chemical reaction has occurred. In each case, identify

an example where you have experienced that observation.

elpmaxEnoitavresbO

a.

b.

c.

d.

e.

86 Inorganic Compounds and Metathesis Reactions

Experiment 4 87

Date __________Lab Sec. _______Name_____________________________________________Desk No. ___________

A. Identification

On a separate sheet of paper, construct a table with the headings shown below. Fill in the table as described in the Experi-

mental Procedure. Submit this data sheet along with your Report Sheet.

niytilibuloSdetciderPetatSlacisyhP

Formula Name (g, l, s) Color Characteristics Water (Appendix G)

Ex. NaCl Sodium chloride Solid White Small, shiny, dry Soluble

1 ____ _________________________ ______________ _______ ______________ __________________

2 ____ _________________________ ______________ _______ ______________ __________________

3 ____ _________________________ ______________ _______ ______________ __________________

B. Metathesis Reactions (Double-Displacement Reactions)

Use the seven steps presented in the Introduction as a guide to writing formulas and equations as you observe the stages of

a chemical reaction.