Properties of Acids and Bases (Adapted from Flinn Scientific Acid Base Test Kit I #AP4567) Introduction Battery acid, stomach acid, acid rain just a few acids in our everyday life! What does it mean when something is acidic? How do acids differ from bases? In this lab, the physical and chemical properties of a variety of acids and bases will be examined. Concepts Acids vs. Bases Indicators ph Background Acids and bases make up two groups of substances that can be categorized by their physical and chemical properties. Let's take a look at the distinguishing properties: 1. Taste: Acids, such as lemons or oranges, taste sour. Bases, such as soap, taste bitter. Note: Taste should never be used to identify a lab chemical or unknown substance. This lab does not include a test using taste. 2. Feel: Acid solutions do not feel much different than water; however, they sting if they contact broken skin. Base solutions have a slippery feeling. Note: Lab chemicals or unknown substances should never be touched with the bare skin. This lab does not include a test using feel. 3. Indicators: An indicator is a chemical compound, either on a test paper or in a solution, that changes color depending on the acidity or basicity of a solution and, thus, is used to test for the presence of acids or bases. There are many different kinds of indicators. Litmus paper and phenolphthalein indicator solution are two of the most common. Blue litmus paper turns red when dipped in an acid solution of ph 1 6. Red litmus paper turns blue when dipped in a basic solution of ph 8 14. In a neutral solution with ph 7, each paper retains its original color. Phenolphthalein indicator solution turns a pink color in a basic solution but remains colorless (sometimes cloudy) in an acidic or neutral solution. 4. Reaction with carbonates: While most bases do not react with carbonates, acids react with carbonates to release carbon dioxide gas. For example: BaC 3 + 2HC1 BaC1 2 + + H 2 5. Reaction with metals : While most bases do not react with metals, acids react with active metals to release hydrogen gas. For example: Fe + 2HCI FeC1 2 + H 2 1
6. Power of Hydrogen Ions ph: Acids are defined as substances that release hydrogen ions (H + ) in solution while bases release hydroxide ions (H ) in solution. The positive hydrogen ion and the negative hydroxide ion combine together to form a neutral water molecule (H 2 ) according to the following equation H + + H > H 2 To express the concentration of hydrogen ions in solution, a term called ph (the power of hydrogen ions) is used. Figure 1 provides ph values for some common substances. ph 1 6: Acidic because the concentration of H + ion is greater than the concentration of the H ion. ph 7: Neutral because the concentrations of H + ion and H ion concentrations are equal. ph 8 14: Basic because the concentration of H ion is greater than the concentration of the H + ion. 7. Electrical conductivity: Strong acids and strong bases split fully into their positive and negative ions and therefore both conduct an electrical current quite well. Weak acids and weak bases remain, for the most part, together and in molecular form (with fewer ions in solution) and thus do not conduct an electrical current well. Materials Needed (for each lab group) Hydrochloric acid solution, 3 M, HC1 Acetic acid solution, 3 M, CH 3 H Sodium hydroxide solution, 1 M, NaH Ammonium hydroxide solution, 1 M, NH 4 H Sodium bicarbonate solution, saturated, NaHC 3 Water, distilled Microplate Red litmus paper Blue litmus paper Phenolphthalein indicator solution ph paper ph indicator color card Universal indicator solution Calcium carbonate (marble chips), CaC 3, 6 pieces Matches Copper wire / pellets, Cu, 3 pieces Magnesium ribbon, Mg, 3 pieces Zinc mossy, Zn, 4 pieces 10 ml graduated cylinder Test tube, small Safety Precautions All of the acids and bases used in this lab are very corrosive to eyes, skin, and other body tissues. They are toxic by ingestion. Avoid all body tissue contact. Acetic acid, hydrochloric acid, and ammonium hydroxide are also toxic by inhalation. Avoid breathing the vapors. Wear chemical splash goggles and wash hands thoroughly with soap and water before leaving the laboratory. 2
Procedure Part A Litmus Paper and Phenolphthalein Indicators 1. Clean the microplate very well to ensure that solutions do not become contaminated. 2. Add 5 drops of each of the following solutions to different wells of your microplate. Make sure to keep track of where you put each solution. If any of the solutions turn pink during this step, wash the microplate again and start over. 3 M HCl (hydrochloric acid) 1 M NH 4 H (ammonium hydroxide) 3 M CH 3 H (acetic acid) Saturated NaHC 3 (sodium bicarbonate) 1 M NaH (sodium hydroxide) Distilled H 2 3. Using a different piece of dry red litmus paper for each of the 6 solutions, dip the end of the litmus paper into the solution. Remove the paper immediately from each solution, record the color of the paper in Table 1, and place the test paper on a piece of paper towel for disposal. 4. Repeat the procedure in step 3, using a different piece of dry blue litmus paper for each of the 6 solutions. After each test, be sure to record the color of the litmus paper in Table 1. Throw the paper towel and all litmus paper in the garbage can. Do NT dispose of the litmus paper in the sink! 5. To each of the 6 solutions in Row 1, add 3 drops of phenolphthalein indicator solution. Record the color of each solution in Table 1. 6. Use your results from steps 2 4 as well as the Background section on Indicators to classify each of the 6 solutions as acidic, basic, or neutral. Record the classification in Table 1. 7. Rinse the microplate with plenty of water and then dry it. Caution: Take care when rinsing the plates so that solution does not splash out. Part B ph Paper and Universal Indicator 8. Add 5 drops of each of the following solutions to different wells of your microplate. Make sure to keep track of where you put each solution. 3 M HCl (hydrochloric acid) 1 M NH 4 H (ammonium hydroxide) 3 M CH 3 H (acetic acid) Saturated NaHC 3 (sodium bicarbonate) 1 M NaH (sodium hydroxide) Distilled H 2 9. Using a different piece of dry ph paper for each of the 6 solutions, dip the end of the paper into the solution. Remove the paper immediately, record the color of the ph paper in Table 1, and place the ph paper on a piece of paper towel for disposal. 10. Use the ph indicator color chart on the ph paper container to assign a numerical ph value to each solution. Record this value in Table 1. Throw the paper towel and all the ph paper in the garbage can. Do NT dispose of the ph paper in the sink! 11. To each of the 6 solutions, add 3 drops of universal indicator solution. Record the color of each solution in Table 1. 12. Use the ph indicator color card for the universal indicator solution to determine the numerical ph value of each solution. Record this value in Table 1. 13. Rinse the microplate with plenty of water and then dry it. Caution: Take care when rinsing the plates so that solution does not splash out. 3
Part C Acid and Base Reactions with Carbonates 14. Add 10 drops of each of the following solutions to different wells of your microplate. Make sure to keep track of where you put each solution. 3 M HCl (hydrochloric acid) 1 M NH 4 H (ammonium hydroxide) 3 M CH 3 H (acetic acid) Saturated NaHC 3 (sodium bicarbonate) 1 M NaH (sodium hydroxide) Distilled H 2 15. To the solution in each well, add a small piece of calcium carbonate, CaC 3. (Note: CaC 3 is sometimes called marble chips.) Allow the reactions, if any, to proceed for 2 minutes. In Table 1, write "yes" or "no" to record the reactivity of each solution with calcium carbonate. 16. Dump the pieces of calcium carbonate (with the solution) from the microplate into the designated Lab Waste container. Do NT dispose of the calcium carbonate chips in the sink! 17. Rinse the microplate with plenty of water and then dry it. Caution: Take care when rinsing the plates so that solution does not splash out. Part D Acids and Bases Reactions with Metals 18. Add the following to three individual wells in Row 1 of your microplate Zinc mossy, 1 small piece Magnesium ribbon, 1 cm piece Copper pellet, 1 piece 19. Add 10 drops of HCl to each well containing a metal piece. (Be sure there is enough solution to cover the metal.) Compare the speeds of reaction of the metals with this acid. In Table 2, record the reactivity (very fast, fast, moderate, slow, very slow, no reaction) of the HCI with each metal tested. 20. In Row 2 of your microplate, repeat steps 18 and 19, using 10 drops of CH 3 H. Be sure to rank the reactivity of the CH 3 H with each metal as you did in step 18. Record the reactivity in Table 2. 21. In Row 3 of your microplate, repeat steps 18 and 19 using 10 drops of NaH. Be sure to rank the reactivity of the NaH with each metal as you did in step 18. Record the reactivity in Table 2. 22. Dump all pieces of metal (with the solution) in the designate Lab Waste container. Do NT dispose of the metals in the sink! 23. Rinse the microplate with plenty of water and then dry it. Caution: Take care when rinsing the plates so that solution does not splash out. Part E Test for Release of a Gas 24. Place 1 small piece of mossy zinc in the 10mL graduated cylinder. 25. Add about 10 drops of HCl to the zinc and promptly place an inverted test tube directly on top of the graduated cylinder so that it completely covers the graduated cylinder and forms a seal. 26. Continue holding the inverted test tube, allowing the reaction to continue for 2 minute or until the reaction stops. 27. Light a match (or have your lab partner light the match) and hold it about 2 inches to the side of the test tube opening. Quickly move the inverted test tube over the match so that the flame is in the opening of the test tube. Record your observations in Table 3. 28. Dispose of any remaining material or solution into the designated Lab Waste Disposal container. 29. Clean the graduated cylinder by rinsing in with plenty of water. (Caution: Take care when rinsing the graduated cylinder so that solution does not splash out.) 4
Data Tables Table 1 Indicators, ph, and Reaction with Carbonates P a r t A P a r t B P a r t C Color of red litmus Color of blue litmus Color with phenolphthalein Acidic, basic, or neutral Color with ph paper ph with ph paper Color with universal indicator ph with universal indicator Reaction with calcium carbonate chip NH HCl CH 3 H NaH 4 H NaHC ( ammoniu 3 ( hydrochloric ( acetic ( sodium m ( sodium acid) acid) hydroxide) bicarbonate) hydroxide) red red blue blue blue red red red blue blue blue blue clear clear pink pink pink clear H 2 (water) acid acid base base base neutral magenta red dark blue green blue green yellow 1 3 11 9 9 7 red red purple blue dark green light green 4 4 10 9 8 7 yes yes no no no no Table 2 Reaction with Acids and Bases with Metals HCl (hydrochloric acid) CH 3 H (acetic acid) NaH (sodium hydroxide) Zinc fast moderate no reaction Magnesium very fast fast no reaction Copper no reaction no reaction no reaction Table 3 Test for Release of Gas Results bservations with burning splint test Zn + HCl 5
Questions and Analysis of Data Part A Litmus Paper and Phenolphthalein Indicators 1. a. Which of the solutions tested are acidic? HCl and CH 3 H b. What evidence do you have for this? they turned blue litmus paper red 2. a. Which of the solutions tested are basic? NaH, NH 4 H, and NaHC 3 b. What evidence do you have for this? they turned red litmus paper blue and phenolphthalein turned pink 3. a. Were any of the solutions neutral (neither acidic nor basic)? Which one(s)? H 2 b. How do you know this? red litmus stayed red, blue litmus stayed blue, phenolphthalein stayed clear 4. Look at your results with the litmus test paper. a. What color is litmus paper in acids? red b. What color is litmus paper in bases? blue c. What color is litmus paper in neutral solutions? each paper stays its original color 5. Look at your results with the phenolphthalein indicator. a. What color is phenolphthalein in acids? clear b. What color is phenolphthalein in bases? pink c. What color is phenolphthalein in neutral solutions? clear/cloudy 6. Using litmus paper and phenolphthalein. a. Red litmus paper turns blue when placed in unknown Chemical A. Is Chemical A an acid, base, or 6
neutral solution? It is a base. b. Blue litmus paper stays blue when placed in unknown Chemical B. Based only on this information, Chemical B could be which type(s) of solutions: acidic, basic, or neutral? It could be a base or neutral solution. c. Phenolphthalein stays clear when placed in Chemical B. Based on this and the information from #6b above, is Chemical B an acid, base or neutral solution? It is a neutral solution. d. Phenolphthalein stays clear in Chemical C. Does red litmus help identify whether it is an acid, base, or neutral? Why or why not? No because both an acid and neutral solution would keep red litmus paper red. We know it s not a base from the phenolphthalein. Part B ph Paper and Universal Indicator 7. Look at the data for the acidic solutions. a. What color(s) were these acids with the ph test paper? magenta and red b. What color(s) were these acids with the universal indicator? red c. What ph values can be assigned to acids? 1 6 8. Look at the data for the basic solutions. a. What color(s) were these bases with the ph test paper? purple, dark blue, dark green, green b. What color(s) were these bases with the universal indicator? purple, dark blue, dark green c. What ph values can be assigned to bases? 8 14 9. Look at the data for the neutral solution. a. What color(s) were these neutral solution(s) with the ph test paper? yellow 7
b. What color(s) were these neutral solution(s) with the universal indicator? light green c. What ph values can be assigned to neutral solution(s)? 7 10. Relate ph to acid or base strength. a. Using the numerical ph values for the acids, rank the acids from strongest to weakest. HCl, CH 3 C 3 H b. Using the numerical ph values for the bases, rank the bases from strongest to weakest. NaH, NH 4 H, NaHC 3 11. a. What would be some benefits of using universal indicator rather than phenolphthalein? It tells you if it is acidic, basic, or neutral. Phenolphthalein just tells you if it is a base or not b. When would phenolphthalein be sufficient as an indicator? If you only wanted to identify bases, then it would be sufficient. 12. Using Indicators Chemical A : a. Blue litmus paper stays Blue in Chemical A. Based only on this test it can be determined that Chemical A is NT which of the following: acidic, neutral, or basic? Acidic b. Red litmus paper stays Red in Chemical A, Based on this test and part A above, is Chemical A an acid, base, or neutral solution? It would be neutral Chemical B : 8
a. Phenolphthalein is placed in a sample of Chemical B and turns pink. Is Chemical B an acid, base, or neutral solution? It is a base. b. Based on the test from part A above, Chemical B could have which of the following ph values? 1, 3, 5, 7, 9 It would be 9 because that is the only ph value of a base. Chemical C : a. Red litmus paper stays Red in Chemical C. Based only on this test, it can be determined that Chemical C is NT which of the following: acidic, neutral, or basic? It is not a base. b. Phenolphthalein stays clear in Chemical C. Based on this test and the test from part A above, Chemical C could be which of the following solutions: acidic, basic, or neutral? It could be neutral or acidic. c. Based on part A and B above, which of the following colors are possible colors for ph paper placed in Chemical C: range, Green, Violet? The possible color is orange because the other colors would be bases. Part C Acid and Base Reactions with Carbonates 13. Which solutions reacted with the calcium carbonate chip? acids 14. The following chemical equations show some of the reactions from Part C of this lab. Are these equations properly balanced or not? a. CaC 3 + 2 HCl CaCl 2 + H 2 + Is this balanced? yes b. CaC 3 + 4 CH 3 H Ca(C 2 H 3 2 ) 2 + 5 H 2 + Is this balanced? no 15. What gas is released in the reaction of acids with carbonates? 16. Using Indicators and Reactions with Carbonates: Chemical A a. Red litmus paper in Chemical A remains red. Based only on this information, Chemical A could be which of the following solutions: acidic, basic, or neutral? acidic or neutral b. A carbonate placed in Chemical A does not react. Based on this information and Part A above, is Chemical A acidic, basic, or neutral? neutral 9
Chemical B c. A carbonate reacts with Chemical B. Based on this information, is Chemical B acidic, basic, or neutral? acidic d. The carbonate reacts very rapidly with Chemical B. Based on this information, which of the following ph values would be most appropriate: 1, 4, 7, 9? Explain why. ph of 1 because the stronger the acid the more rapid the reaction Chemical C e. A carbonate shows no reaction with Chemical C. Based on only this information, Chemical C could NT be which of the following: acidic, basic, or neutral? acidic f. Based on the information from part E above, which type of litmus paper could be used to definitely identify the type of solution? Explain the possible results. Red litmus paper would help because it would stay red in neutral and turn blue in base Part D Acids and Bases Reactions with Metals 17. Rank the three metals tested from most reactive to least reactive. Mg, Zn, Cu 18. Look at your results from Part D. Among the acids and bases that were tested, which solutions showed a reaction with any of the metals? HCl and CH 3 H 19. Write the products for the following single replacement chemical reactions and indicate whether or not the resulting equations are balanced: a. Zn + HCl ZnCl 2 + H 2 Is this balanced? no (product) b. Mg + HCl MgCl 2 + H 2 Is this balanced? no (product) 20. Using Indicators, Reactions with Carbonates, and Reactions with Metals Chemical A 10
a. Phenolphthalein remains clear in Chemical A. Based only on this information, Chemical A could be which of the following solutions: acid, base, or neutral? acid or neutral b. If you add an active metal such as magnesium to Chemical A, there is no reaction. Based on this and Part A above, Chemical A is: acid, base, or neutral? neutral Chemical B c. When sodium carbonate is placed in Chemical B, there is no reaction. Based only on this information, Chemical B could be which of the following solutions: acid, base, or neutral? base or neutral d. Based on the test above, what would expect an active metal to do in Chemical B? not react Chemical C e. Red litmus paper remains red in Chemical C. Based only on this information, Chemical C could be which of the following solutions: acid, base, or neutral? acidic or neutral f. If an active metal, such as magnesium, fizzes just a little bit, would a ph of 1, 4, 7, or 9 be most appropriate? Explain why. 4 because you know it has to be an acid, but it is probably a weaker acid Part E Test for Release of a Gas 21. How do you know that a gas was released during the reaction? There was fizzing and bubbling. A loud sound was also produced. 22. What gas was released when the metals reacted with HCl (see chemical formulas from #19 above)? H 2 or hydrogen gas 23. Write the products for the following synthesis reaction and indicate whether or not the equation is balanced: H 2 + 2 H 2 The equation is not balanced because you start with 2 oxygen and end with 1. 11
Summary Questions 24. For each of the following write Acids, Bases, Both (acids and bases), and/or Neutral a. acids H + is characteristic group g. acid and neutral Phenolphthalein remains colorless b. bases H is characteristic group h. bases Turns phenolphthalein pink c. acids Corrodes (reacts with) metals i. acids Reacts with carbonates d. both and neutral Changes color of ph paper j. acids ph lower than 7 e. bases Turns red litmus blue k. neutral ph equal to 7 f. acids Turns blue litmus red l. bases ph higher than 7 25. Use your textbook and your laboratory data to complete the following acid/base summary table: Category Acids Neutral Bases Examples Taste Feel Effect on Blue Litmus Effect on Red Litmus Effect on Phenolphthalein ph range Reaction with metals Reaction with carbonates Electrical conductivity HCl, lemons H 2 NaH, soap sour no taste bitter feels like water, in cuts it wet slippery stings red blue blue red red blue clear clear pink 1 6 7 8 14 yes no no yes no no strong good conductor no strong good conductor weak bad conductor weak bad conductor 12
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