6-2 Types of Chemical Reactions

 

Many chemical reactions are accompanied by observable physical changes. The appearance of a solid (precipitate) when solutions of substances are mixed is one such change. Others are generation of a gas and a change in the color of a solution. In this laboratory activity, you will observe what happens when a number of different substances are combined. Many of the reactions you will observe can be classified as single displacement, double displacement, decomposition, or synthesis reactions.

 

OBJECTIVES

• Carry out chemical reactions in a microplate.

• Identify the pairs of substances that react.

• Classify the reactions that occur.

• Write balanced equations for the reactions.

 

MATERIALS

microtip pipets

96-well microplate

96-well template

beaker

deionized water

file

drinking straw

goggles

apron

 

PROCEDURE

1. The substances from Group A listed under Data and Observations will each be combined with the substances from Group B. Form a hypothesis about which reactants in Group B might take part in single displacement reactions with reactants in Group A.

Hypothesis:

 

 

2. Label a 96-well template and Microplate Data Form as illustrated under Data and Observations. Use rows A through D for Set 1. Use rows E through H for Set 2.

3. In preparation for the reactions in Set 1, place the microplate on your template so that the numbered columns are away from you and the lettered rows are at the left.

4. CAUTION: Many of the chemicals you will use are toxic. Follow proper chemical hygiene procedures. Wash your hands thoroughly after completing this laboratory activity. Place a few granules of MnO2 in each of wells A1 and A2 of the microplate. These are the only two wells in row A to be used. The MnO2 does not take part in any reaction here, but helps to make reactions occur. CAUTION:

MnO2 is a strong oxident. Contact with organic material should be avoided.

5. Using a microtip pipet, place 4 drops of Cu(NO3)2 solution in each of wells B1 through B11. Rinse the pipet in a beaker of deionized water. Remember to rinse the microtip pipet every time you change chemicals.

6. Place 4 drops of Ni(NO3)2 solution in each of wells C1 through C11.

7. Place 4 drops of Pb(NO3)2 solution in each of wells D1 through D11.

8. Place a 2-cm piece of drinking straw in well A1. Clean a 3-cm strip of magnesium metal with a file. Bend the magnesium so that most of it hangs inside the straw, as shown in the diagram.

9. Temporarily remove the straw-metal assembly. Add 5 drops of 5 percent NaClO solution to the MnO2 in well A1. Carefully replace the straw-metal assembly in well A1 so that the solution does not come in direct contact with the magnesium.

10. Add 1 drop of 6M HCl to well A1 by letting it run down the inside of the straw. The result is generation of chlorine gas, Cl2, to test the combination of magnesium and chlorine. CAUTION: Hydrochloric acid (HCl) is very corrosive. Avoid contact with skin and eyes.

11. Add 5 drops of H2O2 solution to well A2.

12. Add a small piece of clean magnesium to each well in column 1, rows B through D.

13. Add a small piece of zinc to each well in column 2, rows B through D.

14. Add 4 drops of solutions of each of the remaining substances in Group B, one to each column beginning with column 3 and continuing through column 11. For example, add 4 drops of Na2CO3 solution to each of wells B3, C3, and D3; add 4 drops of Na2SO4 solution to each of wells B4, C4, and D4.

15. Record your observations for each combination of reactants in the labeled Microplate Data Form.

16. Discard the mixtures in the microplate according to your teacher’s instructions. Rinse the microplate with deionized water.

17. In preparation for the reactions in Set 2, place the microplate on your lab bench so that the numbered columns are away from you and the lettered rows are at the left.

18. Add 4 drops of the solutions listed in Set 2 of Group A to wells 1 through 11 in rows E through H, one solution to each row. CAUTION: Nitric acid (HNO3) is very corrosive. Avoid contact with skin and eyes.

19. Add a small piece of clean magnesium to each well in column 1, rows E through H.

20. Add a small piece of zinc to each well in column 2, rows E through H.

21. Next, add 4 drops of each of the solutions listed for columns 3 through 11 in Group B to the wells in rows E through H, one solution to each column.

22. Record your observations in the Microplate Data Form.

23. Discard the mixtures in the microplate according to your teacher’s instructions. Rinse the microplate carefully with deionized water.

DATA AND OBSERVATIONS

1. Label a Microplate Data Form as shown in the partial form. In Set 1, the reactants in well A1 are Mg and Cl2; in well A2 the reactant is H2O2. In rows B–D in Set 1 and in rows E–H in Set 2, the row reactants listed in Group A are combined with the column reactants listed in Group B.

Enter your observations in the Microplate Data Form as shown in the partial form, using NR where there is no observable reaction and ppt for formation of a precipitate (include ppt color). X indicates a reaction occurred; you will add these marks as you analyze your observations.

 

OBSERVATIONS

 

1

2

3

4

5

6

7

8

9

10

11

 

Mg

Zn (EXCEPT A2)

Na2CO3

Na2SO4

Na2CrO4

NaCl

NaI

NaSCN

Na2Cr2O7

NaOH

H2O

A SET 1

 

 

 

 

 

 

 

 

 

 

 

B

Cu(N03)2

 

 

 

 

 

 

 

 

 

 

 

C Ni(N03)2

 

 

 

 

 

 

 

 

 

 

 

D Pb(N03)2

 

 

 

 

 

 

 

 

 

 

 

E SET 2

HN03

 

 

 

 

 

 

 

 

 

 

 

F

 AgN03

 

 

 

 

 

 

 

 

 

 

 

G Al(N03)3

 

 

 

 

 

 

 

 

 

 

 

H Fe(N03)3

 

 

 

 

 

 

 

 

 

 

 

 

ANALYSIS

1. On your labeled Microplate Data Form, place an X in the lower right-hand corner of the square for each well where a reaction occurred.

2. In the space below and on page 52 or page 54, write a balanced equation for each combination of substances that resulted in a reaction, labeled as illustrated with the row letters and column numbers. Omit column numbers where no reaction occurred.

Set 1

Row A

Col 1 [balanced equation]

      2  [balanced equation]

You need not write equations for any well where there was a color change but no precipitate formed. The color shows a reaction that formed a different kind of ion in solution.

 

CONCLUSIONS

1. Identify each balanced equation as representing a single displacement (SD), double displacement (DD), synthesis (S), or decomposition (D) reaction. Write the symbol for the type of reaction next to the equation on your list.

 

2. Was your hypothesis about the probable reactants in single displacement reactions correct?

Explain.

 

EXTENSION AND APPLICATION

1. What type of reaction between two ionic compounds in water solution was most common?

2. Which of the substances that you tested most often reacted to form a complex ion, as shown by a color change but no precipitate?

3. From each of three different columns, choose one reaction that you classified as double displacement with precipitate formation. Using the Solubility Guidelines in Table D.8 on page 851 and your balanced equations, identify which of the two products formed in each of the three reactions was the solid.