By: Michael Wild, Matt Huber, Jasmine Gilbert and Dr. Faith Yarberry

Transcription

1 Acid Chemistry By: Michael Wild, Matt Huber, Jasmine Gilbert and Dr. Faith Yarberry In this module the student will: Understand the concept of an Acid. Discover the differences between strong acids and weak acids. Learn the meaning of the term ph with respect to acid / base strength. Uncover what an indicator is and how it works. Identify the strength of an acid and a base in various household products via ph. Be able to define a buffer, prepare a buffer, and understand the purpose of a buffer. Acid Chemistry Page 1

2 Lesson 1: Strengths of Acids The Bronsted/Lowry Definition of an acid is: Acid a substance that donates a proton. Proton the description used for a hydrogen cation (H + ) because once an electron is removed from a hydrogen atom, all that is left is a proton) Example: Hydrochloric acid HCl H + + Cl - When an acid is dissolved in water, hence aqueous (aq), the hydrogen cation is donated to the water forming a hydronium ion (H 3 O + ). Hydrochloric acid HCl (aq) H 3 O + + Cl - Not all acids are created equally. Strong acid an acid that dissociates entirely in water to produce a hydronium ion and an anion. The diagram below shows this relationship. 1 Acid Chemistry Page 2

3 Weak acid an acid that only partially dissociates in water to produce a hydronium ion and an anion. The diagram below shows this relationship. 1 Weak acids reach a state of equilibrium. Equilibrium The point where the concentrations of the reactants and the concentration of the products cease to change, but the reaction itself continues. (1) Initially all that is present are reactants. Acid Chemistry Page 3

4 (2) The reaction moves in a forward direction building the concentration of products. (3) As the concentration of the products build the reverse reaction begins to occur. (4) The forward and the reverse reactions occur simultaneously. The forward reaction continues to make product while the reverse reaction continues to make reactants. At some point the concentration of the reactants and those of the products will cease to change. This point is called equilibrium. Acid equilibrium constants (K a ) indicate the degree to which an acid will dissociate. The diagram below indicates the relationship between K a and dissociation. 1 Acid Chemistry Page 4

5 In the laboratory you are going to prove that the stronger the acid, the greater its reactivity due to the quantity of free H +. To do so, you will be reacting magnesium metal with hydrochloric acid and with acetic acid. You will be collecting the amount of hydrogen produced by each reaction. From the amount of hydrogen produced you will be able to identify the strength of the acid. (LAB 1) Following the lab put up the following table to prove that what they observed was not just a result for acetic acid and hydrochloric acid. The value for trichloroacetic acid is off due to the fact that this material is hygroscopic. Being hygroscopic the concentration of the original solution not likely to be near the 5.0 M region as with the other materials. Acid K a Volume of H + Hydrobromic Acid 1 x ml Hydrochloric Acid 1 x ml Sulfuric Acid 1 x x ml Trichloroacetic Acid 2 x ml Iodic Acid 1.7 x Chloroacetic Acid 1.4 x ml Ascorbic Acid 8 x Acetic Acid 1.8 x ml Propionic Acid 1.32 x ml Water 1 x Phenol 1.3 x Sodium Hydroxide 1.58 x Possible questions: (1) What reason can you give as to why sulfuric acid generates nearly twice the volume of H + compared to hydrochloric acid and hydrobromic acid even though all three are strong acids? (Structure) (2) What reason can you give as to why this method may not have worked for determining the H + content in iodic acid even though its K a resides between that of trichloroacetic acid and acetic acid? (Structure) (3) What do the weak acids have in common that did react with magnesium? (Structure) Acid Chemistry Page 5

6 Compound Compound Structure K a Conc. of Compound Volume of Compound Used Volume of H 2 Generated in 4 minutes Conc of H + Hydrobromic Acid HBr 1 x M ml 55.5 ml M Hydrochloric Acid HCl 1 x M ml 57.5 ml M Sulfuric Acid HO O S O OH 1 x x M 5.00 ml 55.5 ml M Cl O Cl Trichloroacetic Acid C C Cl OH 2 x M ml 43.5 ml ---- Acid Chemistry Page 6

7 Iodic Acid O O I OH 1.7 x M 5.00 ml O Chloroacetic Acid CH 2 C Cl OH 1.4 x M ml 46.0 ml M HO Ascorbic Acid HO O O 8 x M 5.00 ml HO OH Acetic Acid C H 3 O OH 1.8 x M ml 38.0 ml M Acid Chemistry Page 7

8 Propionic Acid H 3 C O CH 2 C 1.32 x M ml 12.0 ml M OH Water H 2 O 1 x M 5.00 ml OH Phenol 1.3 x M 5.00 ml Sodium Hydroxide NaOH 1.58 x M 5.00 ml Acid Chemistry Page 8

9 Lesson 2: ph and Indicators A method for describing the concentration of H + in solution is ph. ph a term used to describe the acidity of a solution through the detection of H + concentration in solution A neutral solution has a ph of 7.0. ph s below 7.0 indicate that the solution is acidic and ph s above 7.0 indicate that the solutions is basic. See the diagram below. 1 The ph of a solution can be determined using an indicator or ph probes. Of these methods the ph probe will give the greatest amount of accuracy regarding ph, but ph probes can be expensive. A much less expensive method for determining the ph of a solution requires the use an indicator. Indicator A substance that changes colors depending on the ph of the solution. ph indicators can be substances such as chemical compounds, litmus papers etc that when added in small quantities to a solution visually allow us to determine the relative acidity or basicity of a solution by undergoing a change in color. Indicators are usually, themselves, either a weak acid or base that detect the hydrogen ion concentration in solution. Below is a table of indicators, the color of that indicator below the lowest ph indicated, the range for which a color change will be detectable, and the color of that indicator above the highest ph indicated. 2 Acid Chemistry Page 9

10 Indicator Color Below Color Above ph Range Lowest ph Highest ph Methyl violet Yellow 0.5 to 2.0 Violet Thymol Blue Red 1.2 to 2.8 Yellow Yellow 8.2 to 9.1 Blue Methyl Orange Red 3.1 to 4.4 Yellow Methyl Red Red 4.2 to 6.3 Yellow Bromocresol Green Yellow 3.8 to 5.4 Blue Alizarin Yellow 5.7 to 7.1 Red Red 11.0 to 12.4 Purple Bromothymol Blue Yellow 6.0 to 7.6 Blue Phenol Red Yellow 6.4 to 8.0 Red Cresol Red Yellow 7.0 to 8.8 Red Phenolphthalein Colorless 8.0 to 9.8 Red Thymolphthalein Colorless 9.3 to 10.5 Blue By using a combination of indicators it is possible to determine the relative ph. Lab #2. There are many plants that contain chemicals that can be used as natural ph indicators such as the anthocyanin compound family. Red cabbage is part of that anthocynanin containing family. These compounds will usually turn acidic solutions a red color, basic solutions a green-yellow color, and neutral solutions a purple color. Due to this result it is possible that one can use red cabbage to find the ph of a solution as seen in the photograph below.. Acid Chemistry Page 10

11 At this point have the students bring household products for class the following day to test the ph of the solution in Lab 3. We have stated that the ph of the solution allows us to determine the concentration of the H + in solution. What is the connection? ph = -log [H + ] Your assignment tomorrow, is to determine the approximate H + concentration in each of the household solutions studied today. 10 -ph = [H + ] The next day the students will come in with the H + concentration determined. Ideally you should come in with the real H + concentration of the solution (ph probe). That way the students can see that the indicator does a fairly good job of predicting the H + concentration. Acid Chemistry Page 11

12 Lesson 3: Buffers Some solutions, called buffers, are remarkably resistant to changes in ph. Water is not a buffer, since its ph is very sensitive to the addition of acidic or basic species. A good buffer, again, is a system that will prevent drastic changes in ph. Buffers are usually solutions of a weak acid and their conjugate base. A conjugate base results when the weak acid loses its acidic hydrogen. Below are a couple of examples. Acid Conjugate Base Acetic Acid HC 2 H 3 O 2 - Acetate ion C 2 H 3 O 2 2- Dihydrogen phosphate HPO 4 3- Phosphate PO 4 In lab today you are going to prove that a buffer is used to prevent ph changes. Lab 4 and/or 5. Acid Chemistry Page 12

13 Overheads Acid Chemistry Page 13

14 Lesson 1 Definitions Acid a substance that donates a proton. Proton the description used for a hydrogen cation (H + ) because once an electron is removed from a hydrogen atom, all that is left is a proton) Strong acid an acid that dissociates entirely in water to produce a hydronium ion and an anion. Weak acid an acid that only partially dissociates in water to produce a hydronium ion and an anion. Equilibrium The point where the concentrations of the reactants and the concentration of the products cease to change, but the reaction itself continues. Acid equilibrium constants (K a ) indicate the degree to which an acid will dissociate. Acid Chemistry Page 14

15 Lesson 2 Definitions ph a term used to describe the acidity of a solution through the detection of H + concentration in solution Indicator A substance that changes colors depending on the ph of the solution. ph = -log [H + ] 10 -ph = [H + ] Acid Chemistry Page 15

16 Lesson 3 Definitions Buffer A material that prevents the ph of a solution from changing drastically upon addition of an acid or a base. Acid Chemistry Page 16

17 Acid Chemistry Page 17

18 Acid Chemistry Page 18

19 Acid K a Volume of H + Hydrobromic Acid 1 x ml Hydrochloric Acid 1 x ml Sulfuric Acid 1 x x ml Trichloroacetic Acid 2 x ml Iodic Acid 1.7 x Chloroacetic Acid 1.4 x ml Ascorbic Acid 8 x Acetic Acid 1.8 x ml Propionic Acid 1.32 x ml Water 1 x Phenol 1.3 x Sodium Hydroxide 1.58 x Acid Chemistry Page 19

20 Compound Compound Structure Compound Structure Hydrobromic Acid HBr Iodic Acid O O I OH Propionic Acid H 3 C CH 2 O C OH O Hydrochloric Acid HCl Chloroacetic Acid CH 2 C Cl OH Water H 2 O HO Sulfuric Acid HO O S OH Ascorbic Acid HO O O Phenol OH O HO OH Trichloroacetic Acid Cl Cl C Cl C O OH Acetic Acid C H 3 O OH Sodium Hydroxide NaOH Acid Chemistry Page 20

21 Acid Chemistry Page 21

22 Indicator Color Below Color Above ph Range Lowest ph Highest ph Methyl violet Yellow 0.5 to 2.0 Violet Thymol Blue Red 1.2 to 2.8 Yellow Yellow 8.2 to 9.1 Blue Methyl Orange Red 3.1 to 4.4 Yellow Methyl Red Red 4.2 to 6.3 Yellow Bromocresol Green Yellow 3.8 to 5.4 Blue Alizarin Yellow 5.7 to 7.1 Red Red 11.0 to 12.4 Purple Bromothymol Blue Yellow 6.0 to 7.6 Blue Phenol Red Yellow 6.4 to 8.0 Red Cresol Red Yellow 7.0 to 8.8 Red Phenolphthalein Colorless 8.0 to 9.8 Red Thymolphthalein Colorless 9.3 to 10.5 Blue Acid Chemistry Page 22

23 Acid Conjugate Base Acetic Acid HC 2 H 3 O 2 - Acetate ion C 2 H 3 O 2 2- Dihydrogen phosphate HPO 4 3- Phosphate PO 4 Acid Chemistry Page 23

24 Acid Chemistry Page 24

25 Laboratory Experiments Acid Chemistry Page 25

26 Acid Chemistry Page 26

27 Laboratory #1 Preparation (for nine groups): 0.5 M HCl Slowly add 8.3 ml of 6 M hydrochloric acid to approximately 50 ml of distilled water in a 100 ml volumetric flask. Cap and shake. Then add distilled water to the line, cap and shake. 0.5 M Acetic Acid Slowly add 2.90 ml of glacial acetic acid to approximately 50 ml of distilled water in a 100 ml volumetric flask. Cap and shake. Then add distilled water to the line, cap and shake. Or 0.5 M Acetic Acid Add ml of vinegar to a 100 ml volumetric flask. Add some distilled water, cap and shake. Then add distilled water to the line, cap and shake. Magnesium strips cut into small pieces. Determine the barometric pressure Stop Watch Materials Needed Per Group 10 ml graduated cylinder Large test tube Small test tube Large Erlenmeyer flask Rubber tubing with stopper and glass tubing 100 ml graduated cylinder 600 ml beaker Sink or trash can of water Thermometer Apparatus used (see next page) 3 Acid Chemistry Page 27

28 Acid Chemistry Page 28

29 Background: An acid, when reacted with magnesium metal, dissociates to form hydrogen gas. This gas can be collected and evaluated to determine the relative strength of an acid. This lab will allow you to determine the relative acidities of two different acids; one will be a strong acid and the other a weak acid. The method used in this laboratory involves collecting the gas generated by the magnesium / acid reaction above water in a closed container. In order to determine the amount of hydrogen collected, and hence the strength of the acid, you will be using the ideal gas law to solve for the number of moles of hydrogen generated. The ideal gas law is: PV = nrt, where P stands for the pressure of the gas, V the volume of the gas, n the number of moles of gas, R the ideal gas constant, and T the temperature of the gas in Kelvin. The ideal gas constant comes in many forms, but the one that you will be using for this lab is R = atm L / mol K. The ideal gas constant dictates the units that are acceptable for pressure (atm), volume (L), and temperature (K). The volume and temperature, associated with the gas, will be simple to determine. The volume of the gas will be measured directly from the 100-mL graduated cylinder. This method of measurement is acceptable since gases spread out to fill the space available. The temperature of the gas will be the same as the temperature of the water that the gas bubbled through. The pressure is the most complicated of the variables to determine. The surface molecules of a liquid absorb energy to break free of the remaining liquid molecules and enter into the gas phase. This energy is provided by heat. In this experiment, the amount of water that will enter into the gas phase is determined by the temperature of the water. The higher the temperature of the water, the greater the amount of water molecules that will break free from the liquid phase to enter into the gas phase. So the gas collected in the 100-mL graduated cylinder will be a combination of water (water vapor) and hydrogen. According to Dalton s Law of Partial Pressure, the overall pressure associated with a gas is equal to the sum of the pressures of every gas involved. In this experiment, therefore, the total pressure of the gas, which is barometric pressure, will be the sum of the pressure of the water molecules (water vapor) plus the pressure of the hydrogen gas. P total = P water + P hydrogen To solve for the pressure of the hydrogen gas, the equation can be rearranged to give: P total P water = P hydrogen Once the pressure, volume, and temperature of the hydrogen has been determined, the ideal gas law can be used to calculate the number of moles of hydrogen generated by the acid. Important pressure conversion units: 1 atm = 760 torr 1 atm = 760 mm Hg 25.4 torr = 1 in Hg Acid Chemistry Page 29

30 Procedure 1. Lower a 600-mL beaker into a filled sink of water. 2. Lower a 100-mL graduated cylinder into a filled sink of water. Allow the cylinder to completely fill with water so that no air bubbles remain in the cylinder. 3. While the 600-mL beaker and the 100-mL graduated cylinder are under water, place the cylinder into the beaker. 4. Measure the temperature of the water in the beaker. 5. Obtain approximately grams of magnesium and record the weight. 6. Place the magnesium in a small test tube. 7. Obtain a clean, dry 10-mL graduated cylinder. Place 10-mL of acid into the cylinder and record the volume to the nearest 0.1 ml. 8. Pour the acid into the large test tube. 9. Gently slide the small test tube into the large test tube. Make sure that none of the acid splashes into the tube with the magnesium. 10. Stand the large test tube in an Erlenmeyer flask. 11. Put the stopper end of the tubing into the large test tube so that the seal is tight. 12. Place the other end of the tubing with the curved glass gently under the lip of the 100-mL graduated cylinder. Be careful not to let any air into the cylinder during this step. 13. Carefully mix the acid and magnesium by slowly tilting the large test tube. Bubbling will occur. 14. Continue mixing for 4 minutes. 15. Read the volume of the gas in the graduated cylinder. 16. Carefully pour the resulting solution down the drain capturing any magnesium that remains. 17. Dry the magnesium and weigh it. Record the new weight. 18. Clean your glassware and repeat for the next acid. (You may use the magnesium left from step 15 for your next acid.) Water Vapor Table Temperature in o C Water Vapor Pressure in Torr Acid Chemistry Page 30

31 Data and Results Acid 1 Acid 2 Temperature in o C Temperature in K Initial Mass of Magnesium in g Final Mass of Magnesium in g Mass of Magnesium used Atmospheric Pressure Atmospheric Pressure in atm Water vapor press at this temperature Water vapor in atm Pressure of H 2 (atmospheric pressure in atm water vapor pressure in atm) Volume of gas collected in ml Volume of gas in L Ideal Gas Constant Moles of Hydrogen (H 2 ) Acid Chemistry Page 31

32 Conclusions and Post Lab Questions 1. What is the concentration of the H + in solution for Acid 1? a. You used 10 ml of acid solution in this experiment. What is the volume in liters? b. How many moles of H + is present in the solution if 2 moles of H + gives 1 mole of H 2? c. What is the molarity of the H + in solution if Molarity (M) equals moles of solute divided volume of solution? 2. What is the concentration of the H + in solution for Acid 2? a. You used 10 ml of acid solution in this experiment. What is the volume in liters? b. How many moles of H + is present in the solution if 2 moles of H + gives 1 mole of H 2? c. What is the molarity of the H + in solution if Molarity (M) equals moles of solute divided volume of solution? 3. Which acid, Acid 1 or Acid 2, was the strongest? Explain. Acid Chemistry Page 32

33 Laboratory #2 Preparation (for nine groups): 0.1 M Acetic Acid Slowly add 0.57 ml of glacial acetic acid to approximately 50 ml of distilled water in a 100 ml volumetric flask. Cap and shake. Then add distilled water to the line, cap and shake. 0.01% Malachite Green indicator Dissolve 0.01 g Malachite Green in enough water to make 100 ml of solution. 0.10% Congo Red indicator Dissolve 0.1 g Congo Red in enough water to make 100 ml of solution. 1.0 % Crystal Violet indicator Dissolve 1 g Crystal Violet in enough water to make 100 ml of solution. 0.1% Methyl Orange indicator Dissolve 0.1 g Methly Orange in enough water to make 100 ml or solution. 0.04% Thymol Blue indicator Dissolve 0.04 g Thymol Blue in enough water to make 100 ml of solution. 0.02% Methyl Red indicator Dissolve 0.02 g Methyl Red in enough water to make 100 ml of solution. Materials Needed Per Group 6 test tubes 10 ml graduated cylinder Stirring rod Acid Chemistry Page 33

34 Procedure: 1. Obtain 6 test tubes and label them #1 - #6. 2. Place 1.0 ml of 0.10 M acetic acid in each of the six test tubes. 3. Add 2 drops of crystal violet to test tube #1. 4. Add 2 drops of thymol blue to test tube #2. 5. Add 2 drops of methyl orange to test tube #3. 6. Add 2 drops of congo red to test tube #4. 7. Add 2 drops of malachite green to test tube #5. 8. Add 2 drops of methyl red to test tube #6. Data For each indicator, color in the box on that line that most accurately describes the color you observed in that test tube. Acid Chemistry Page 34

35 Conclusions 1. According to Crystal Violet the ph was between. 2. According to Thymol Blue the ph was between. 3. According to Methyl Orange the ph was between. 4. According to Congo Red the ph was between. 5. According to Malachite Green the ph was between. 6. According to Methyl Red the ph was between. 7. According to all indicators the ph of this solution was between. 8. Explain how indicators can be used to discern the ph of a solution. Acid Chemistry Page 35

36 Acid Chemistry Page 36

37 Laboratory #3 Preparation: Pull and tear the cabbage leaves into small pieces until you fill a large beaker or another container and add water to submerge the leaves. Then add heat to boil the water for approximately 5 to 7 minutes or till the color of the water is purple like the cabbage. Pour up this solution into dropper bottles. Make a laminated sheet of the photograph showing the color of cabbage juice in solution depending on ph for each station. Have your students bring in a sample of a household product that is clear and relatively colorless. Materials Needed per Station: 5-8 test tubes per group Droppers for each sample they will be testing Dropper bottle of cabbage juice solution Photograph showing the color of cabbage juice in solution depending on ph Acid Chemistry Page 37

38 Procedure 1. Add 1 dropper full of the solution to be analyzed to a test tube. 2. Add 5 drops of cabbage juice extract to the test tube. 3. Compare to the photograph to determine the ph of the household product. Data Household Product Color of Solution after Cabbage Juice Addition Approx. ph Acid Chemistry Page 38

39 Conclusions and Post-Lab Questions 1. If the ph of your household product is less than 7, what does it tell you about the amount of H + in your household product compared to those with a ph greater than 7? 2. Place the household chemicals that you tested in order of increasing acidity. 3. Which of your household products has the greatest amount of H + in solution? Acid Chemistry Page 39

40 Acid Chemistry Page 40

41 Laboratory #4 Preparation: (per 20 groups) 0.1 M acetic acid - Dilute ml of store bought vinegar solution to make 500 ml of solution. 0.1 M acetate dissolve 6.56 g of sodium acetate in enough water to make 800 ml of solution. Materials: 100-mL graduated cylinder 150-mL beaker or a glass Straw 0.1 M acetic acid 0.1 M acetate solution ph probe Discussion: They should observe that the ph drops. This is due to the fact that carbon dioxide, exhaled by the body, when combined with water makes carbonic acid. CO 2 + H 2 O H 2 CO 3 The addition of carbonic acid to water that includes a buffer does not affect the ph to appreciable amounts. Acid Chemistry Page 41

42 Procedure: 1. Fill a glass with 60 ml of distilled water 2. Check the ph with a ph probe and record the ph. 3. Using a straw, blow bubbles into the water for 1 minute 4. Retest the ph and record. 5. Clean out your glass. 6. Add 15 ml of 0.1 M acetic acid to the glass. 7. Add 15 ml of 0.1 M acetate to the glass. 8. Add 30 ml of distilled water to the mixture. 9. Check the ph with a ph probe and record the ph. 10. Using a straw, blow bubbles into the water for 1 minute. 11. Retest the ph and record. 12. Clean out your glass. Data ph of distilled water ph of water after 1 minute of bubbles ph of the 15 ml/15 mlbuffer solution ph of buffer solution after 1 minute of bubbles Acid Chemistry Page 42

43 Post-Laboratory Questions 1. Give the name and formula for the acid that you used to make the buffer solution. 2. Give the name and formula of the conjugate base used to make the buffer. 3. How do the acid and the conjugate base differ from one another? 4. Given your observations, explain how a buffer works. 5. What do you think will happen to the ph of your solution when the buffer is used up? 6. Given your observations from the first experiment, explain why it is essential that all living systems contain buffers. Give an example. Acid Chemistry Page 43

44 Acid Chemistry Page 44

45 Laboratory #5 Preparation: (Enough for 14 groups) Buffer solution add 0.75 g baking soda to 350-mL of distilled water. Acid Rain solution add 4 ml of 1 M H 2 SO 4 to 2 L of distilled water. Universal Indicator - Pull and tear red cabbage leaves into small pieces until you fill a large beaker or another container and add water to submerge the leaves. Then heat to boil the water for approximately 5 to 7 minutes or till the color of the water is purple like the cabbage. Pour up this solution into dropper bottles. Materials: Distilled water Buffer solution Acid Rain solution Universal indicator solution ml beakers 1 25 ml graduated cylinder 1 10 ml graduated cylinder Dropper Safety goggles 1 M hydrochloric acid Acid Chemistry Page 45

46 Procedure: 1. Using a 25-mL graduated cylinder add 25-mL of distilled water to one of the beakers 2. Using a 25-mL graduated cylinder add 25-mL of buffered solution to the second beaker. 3. Wash the 25-mL graduated cylinder. 4. Using a 25-mL graduated cylinder add 25-mL of 1 M hydrochloric acid to the third beaker for defining what is meant by the color pink. 5. Wash the 25-mL graduated cylinder. 6. Add 6 drops of universal indicator to each beaker. Record the color of the solutions. 7. Using a dropper add the acid rain solution drop-by-drop to the beaker containing distilled water. Swirl after each addition and record the color. Continue until the color turns pink and remains stable. 8. Using a 10-mL graduated cylinder, add 10-mL of acid rain solution to the beaker with the buffered solution. Swirl after each addition and record the color of the solution. Continue adding acid rain until the solution turns pink and remains stable. Acid Chemistry Page 46

47 Data: Color of HCl solution Distilled Water Buffer Solution Initial Color Color After: 1 drops 2 drops 3 drops 4 drops 5 drops 6 drops 7 drops 8 drops 9 drops 10 drops 11 drops 12 drops 13 drops 14 drops 15 drops 10 ml 20 ml 30 ml 40 ml Acid Chemistry Page 47

48 50 ml 60 ml 70 ml 80 ml 90 ml 100 ml 110 ml 120 ml 130 ml 140 ml 150 ml Volume of Acid Used: (assume 20 drops equals 1 ml) Acid Chemistry Page 48

49 Post Laboratory Questions 1. Why was there a difference in the amount of acid rain needed to change the ph of these two solutions? 2. What is a buffer? 3. Acidosis in the human body occurs when the ph of the blood drops below Alkalosis in the human body occurs when the ph goes above Both are dangerous and can cause death. During a regular day an individual is likely to have a carbonated beverage with a ph around 3 or coffee with a ph of 5. What does the blood contain so that the things that we ingest do not harm us? Acid Chemistry Page 49