Ch. 18Chemical Reactions
Lab #26 A
Name_____________________________
Per_____Date______________________
Lab Partner________________________
A Study of Chemical Reactions
A chemical reaction is a rearrangement of atoms in which bonds are broken and/or
formed. Heat is absorbed or released. We cannot observe bonds breaking or forming
directly. We can determine the overall heat generated by the making and breaking of
bonds. If the overall heat causes the temperature of water to rise the reaction is
exothermic. If the overall heat causes the temperature of water to decrease the reaction is
endothermic.
Evidence that a chemical reaction has taken place.
A precipitate is formed. If a precipitate is formed, new stronger bonds must have
formed, which cannot be broken by reactions with the other chemicals available.
A gas forms. If a gas forms, new bonds must have formed and/or old bonds must have
been broken to make a new substance not previously present.
A color change. Most color change is the result of energy changes that electrons
experience.
Heat is absorbed or released. Bonds breaking takes energy, and formation of bonds
releases energy. Often these are not equal and the overall reaction is endothermic or
exothermic.
Procedure: Test 1
WEAR GOGGLES AT ALL TIMES
1. Record the starting temperature of 5 ml of tap water in a clean test tube. T0 ________
2. Using a spatula from the front desk add 2 pellets of NaOH (a strong base) to the water
in the test tube. BE CAREFUL AS NaOH IS CORROSIVE TO HUMAN TISSUE
3. Gently stir the pellets with the thermometer until they dissolve.
4. Feel the bottom of the test tube for any possible sign of a reaction.
5. Record the final temperature. Tf ________
6. Does this indicate exothermic or endothermic reaction? _______________________
Save this sample for Test 2
Procedure: Test 2
WEAR GOGGLES AT ALL TIMES
7. Using the test tube from Test #1 above, add 2 drops of an indicator, phenolphthalein.
8. What indication is there that a chemical reaction took place? ___________________
9. What does this indicate about the color of phenolphthalein when it is mixed with a
base? ______________________________________________________________
Save this sample to compare with test 3 & 4
Procedure: Test 3
WEAR GOGGLES AT ALL TIMES
10. Record the starting temperature of 2 ml of tap water in a clean test tube. T0 ________
11. Add 15 drops, a drop at at time, of 12 M sulfuric acid H2SO4 to the water. BE
CAREFUL AS SULFURIC ACID IS CORROSIVE TO THE HUMAN BODY.
12. What is the rule for mixing water and acid? _________________________________
13. Feel the bottom of the test tube for any possible sign of a reaction.
14. Record the final temperature. Tf ________
15. Does this indicate exothermic or endothermic reaction? _______________________
Save this sample for Test 4
Reference: Lab Manual Exp. # 27
Ch. 18Chemical Reactions
Lab #26 A
Name_____________________________
Per_____Date______________________
Lab Partner________________________
Procedure: Test 4
WEAR GOGGLES AT ALL TIMES
16. Using the test tube from Test #3 above, add 2 drops of an indicator, phenolphthalein.
17. What indication is there that a chemical reaction took place? ___________________
18. What does this indicate about the color of phenolphthalein when it is mixed with an
acid? ______________________________________________________________
Clean both test tubes for use in the next part
Procedure: Test 5
WEAR GOGGLES AT ALL TIMES
19. Record the starting temperature of 5 ml of tap water in a clean test tube. T0 ________
20. Using a spatula from the front desk add one small scoop of ammonium chloride
NH4Cl to the water in the test tube.
21. Gently stir the mixture with the thermometer until it dissolves.
22. Feel the bottom of the test tube for any possible sign of a reaction.
23. Record the final temperature. Tf ________
24. Does this indicate exothermic or endothermic reaction? _______________________
Procedure: Test 6
WEAR GOGGLES AT ALL TIMES
25. Record the starting temperature of 5 ml of tap water in a clean test tube. T0 ________
26. Using a spatula from the front desk add one small scoop of ammonium nitrate
NH4NO3 to the water in the test tube.
27. Gently stir the mixture with the thermometer until it dissolves.
28. Feel the bottom of the test tube for any possible sign of a reaction.
29. Record the final temperature. Tf ________
30. Does this indicate exothermic or endothermic reaction? _______________________
Clean both test tubes for use in the next part
Procedure: Test 7
WEAR GOGGLES AT ALL TIMES
31. Add 5 drops of a 0.1 M sodium chloride NaCl solution to a clean test tube.
32. Add 5 drops of a 0.1 M potassium bromide KBr solution to the same test tube.
33. Note your observations. _______________________________________________
34. Why did you know there would be no reaction before you even mixed them?
___________________________________________________________________
35. Add 1 drop of a 0.1 M Lead II Nitrate Pb(NO3)2 solution to the same test tube.
36. Note your observations. _______________________________________________
37. Add 1 more drop of a 0.1 M Lead II Nitrate Pb(NO3)2 solution to the same test tube
but let the drop run down the side of the test tube.
38. Add 1 drop of a 0.1 M potassium iodide KI solution to the same test tube but let the
drop run down the side of the test tube.
39. Note your observations. _______________________________________________
40. Write the net ionic equation for all the precipitates that formed. Indicate the color of
the precipitates in each reaction. DISCARD WASTE AT THE FRONT DESK.
Reference: Lab Manual Exp. # 27
Ch. 18Chemical Reactions
Lab #26 A
Name_____________________________
Per_____Date______________________
Lab Partner________________________
Procedure: Test 8
WEAR GOGGLES AT ALL TIMES
41. Add 5 drops of a 0.1 M potassium thiocyanate KSCN solution to a clean test tube.
42. Add 1 drops of a 0.1 M Iron III Chloride FeCl3 solution to the same test tube.
43. Note your observations. _______________________________________________
44. Write the net ionic equation for this reaction.
___________________________________________________________________
45. Add enough tap water slowly to make the color disappear. About 10 ml.
46. Is dilution a chemical reaction? _________________________________________
47. Add 5 more drops of 0.1 M KSCN solution & 1 drop of 0.1 M FeCl3.
48. Note your observations. _______________________________________________
49. Does concentration affect a chemical reaction? _____________________________
50. Shake the test tube. Note your observations. _______________________________
51. Is there any indication that the reaction has reached an equilibrium? Explain.
__________________________________________________________________
DISCARD WASTE with plenty of water.
Procedure: Test 9
WEAR GOGGLES AT ALL TIMES
52. Arrange 5 test tubes in order in a test tube rack.
53. Add a small marble chip to each test tube. Marble is CaCO3 calcium carbonate.
54. Add sufficient acid to each test tube to cover the entire marble chip.
55. Use the following acids: #1 – 6 M
HCl
Be Careful Corrosive
#2 - 6 M
CH3COOH Be Careful Corrosive
#3 - 1 M
HCl
Be Careful Corrosive
#4 - 1 M
CH3COOH Be Careful Corrosive
#5 - 0.1 M
HCl
Be Careful Corrosive
56. What indication is there that a reaction is taking place? _____________________
57. Record the relative rates of each reaction. Place them in order of fastest to slowest.
__________________________________________________________________
58. Predict what gas is being released? ______________________________________
59. What two tests could be used to predict which gas?
___________________________________________________________________
60. What effect would heating the acid marble solution by 10o C have on its rate?
_________________ by 20o C ______________ by 50o C____________________
Conclusions and Questions:
1. Which test(s )indicated an exothermic reaction? ______________________________
2. Which test(s) indicated an endothermic reaction? _____________________________
3. Which test(s) indicated a new phase? ______________________________________
4. Which test(s )indicated no evidence of a chemical reaction? ____________________
Reference: Lab Manual Exp. # 27
Ch. 18Chemical Reactions
Lab #26 A
Name_____________________________
Per_____Date______________________
Lab Partner________________________
5. Use test #9 , HCl as an example and explain how the concentration of the acid affects
reaction rate. Be specific. How does 6M compare to 1M and 0.1 M?
6. Use test #9 as an example and explain how the concept of nature of reactants affects
reaction rate. Choose to compare 6M HCl with 6M CH3COOH.
7. Which acid is considered stronger between HCl and CH3COOH. Site a specific
example that illustrates this.
8. Write the sequence of reactions that took place in test #7. What do you know about the
solubility of K+, Na+ and NO3 -?
Reference: Lab Manual Exp. # 27