Acid-Base Solutions and pH ScaleInvestigation of Acids-Bases

Computer Simulation Activity: Acid-Base Solutions and pH Scale Investigation of Acids-Bases Name:__________________________________________ Part A. Introduction 1. Check out both the Introduction and Custom Solution tabs. Explore what factors affect pH. List the factors you found that affect pH. Investigating Concentration Changes 2. a. Create a strong acid solution in the “Custom Solution” tab. b. Drawbar graphs for Initial and Equilibrium concentrations. Hints: No calculator needed – try the ‘Equilibrium Concentration’ view. Don’t forget to label your graphs! Initial Concentrations Equilibrium Concentrations c. What equilibrium concentrations are affected by changing the initial concentration? There is no change in the reactant side but there is slight increase in the product side 3. a. Create a weak acid solution in the “Custom Solution” tab. b. Draw bar graphs for Initial and Equilibrium concentrations. Hints: No calculator needed – try the ‘Equilibrium Concentration’ view. Don’t forget to label your graphs! Initial Concentrations Equilibrium Concentrations Computer Simulation Activity: Acid-Base Solutions and pH Scale c. What equilibrium concentrations are affected by changing the initial concentration? The reactant side is negatively affected, which means that the equilibrium concentration on the product side is decreasing while it is increasing on the reactant side 4. Are your results for the strong and weak acid in questions 2 and 3 consistent with the definition of strong and weak acids? Yes, the results in questions 2 and 3 for weak and strong acids are consistent with my definitions. Strong acids will entirely dissociate to generate H+ ions, whereas weak acids will only partially dissociate to produce some H+ ions. Investigating the Effects of Acid Strength and Concentration 5. a. What does the ‘strength’ slider (in the sim) effect? The amount of HA on the reactant side will be affected by the strength slide. Strong acids contain no HA because they dissolve fully, but weak acids have some HA because they dissolve only partially. b. What does the term ‘strength’ mean? (In your own words) The strength of the reactant particles indicates how rapidly they will dissociate. 6. How does strength affect the pH of acids? As more H+ ions are dissociated by a strong acid, the pH decreases. 7. How does initial concentration affect the pH of acids? The initial concentrations will define whether the solution is acidic or basic, as well as where on the spectrum they will lie. 8. a.Is it possible for a solution of weak acid and a solution of strong acid to have the same pH? Design and carry out an experiment using the simulation to answer this question. What are your results? Yes, but the weak acid would have to be much more concentrated. The concentration of hydrogen ions in a solution determines the pH. The amount of hydrogen ions donated by a strong acid is proportional to its concentration. A weak acid, on the other hand, cannot fully dissociate and so it cannot donate all of its hydrogen ions to the solution. b. What was your strategy for testing whether a solution of strong acid and a solution of weak acid can have the same pH? To accomplish this, the stronger acid had to have a lower mol/L and the weaker acid had to have a higher mol/L. Water can also be added to the solution to lower the pH. Computer Simulation Activity: Acid-Base Solutions and pH Scale Part B. Investigation of Acids-Bases and pH Scale Name:__________________________________________ pH Scale Simulation Directions: 1. a. There are 3 Parts to the Simulation i. Macro ii. Micro iii. My Solution 2. Start with the Micro Option Part I: Pre-Simulation Research Questions 1. Research the following definitions of acids and bases. a. Arrhenius Definition ● An Arrhenius acid is a chemical that dissociates into hydrogen ions when it comes into contact with water. ● An Arrhenius base is a chemical that dissociates in water to produce hydroxide ions. b. BrØnsted-Lowry Definition ● A Bronsted-Lowry acid is a kind of acid that is capable of donating a proton H+. ● A Bronsted-Lowry base is a kind of base that can take a proton and needs a lone pair of electrons to bind to the H+. c. Lewis Definition ● A Lewis acid is a substance that may receive a pair of nonbonding electrons such as H+ ion. ● A Lewis base is a substance that may give a pair of nonbonding electrons such as the OH- ion. Part II: Macro 1. Create a table in Google Sheets with the following columns. a. pH, [H3O+], [OH-], Product of [H3O+] & [OH-] b. Each row of the table will be for the 11 available substances. c. Using the pH Meter, measure and record the pHs of all 11 substances. Computer Simulation Activity: Acid-Base Solutions and pH Scale pH [H3O+] [OH-] [H3O+] & [OH-] Drain cleaner 13 1.00 E-13 1.00E-01 1.00E-14 Handsoap 10 1.00E-10 1.00E-04 1.00E-14 Blood 7.4 4.00E-08 2.50E-07 10.00E-15 Spit 7.4 4.00E-08 2.50E-07 10.00E-15 Water 7 1.00E-07 1.00E-07 10.00E-15 Milk 6.5 3.20E-07 3.20E-08 1.00E-14 Chicken soup 5.8 1.60E-06 6.30E-09 1.00E-14 Coffee 5 1.00E-05 1.00E-09 1.00E-14 Orange Juice 3.5 3.20E-04 3.20E-11 1.00E-14 Soda pop 2.5 3.20E-03 3.20E-12 1.00E-14 Vomit 2 1.00E-02 1.00E-12 10.00E-15 Battery acid 1 1.00E-01 1.00E-13 1.00E-14 Questions 1. What is the pH range for an acid? Below 7.0 is acidic 2. What is the pH range for a base? Above 7.0 is basic. 3. When is a solution considered neutral? What pure substance has a pH of 7? 7.0 is considered as neutral pH . Example: water. 4. What happens to the pH of the solution when more of the substance is added? When more material is added to the simulation, the pH of the solution does not alter. 5. What happens to the pH of the solution when water is added to the solution? The pH of the solution will become more neutral. 6. What does pH measure? (Research) The acidity or alkalinity of a solution is measured by its pH. The pH of a solution indicates the amount of hydrogen ions present. The greater the H+ concentration, the more acidic the material, and the lower the concentration, the more basic the substance. Computer Simulation Activity: Acid-Base Solutions and pH Scale 7. What basic equation is used to calculate the pH of a solution? (Research) pH=-log[H3O+] Part III: Micro 1. Switch over to the Micro Option of the simulation. 2. Record the concentrations for the H3O+ and OH- ions for each solution in the data table. a. Use the following format : for 1.0 x10-7 type in 1.0 E-7 3. Calculate the product of the two ions ( [H3O+], x [OH-] ) and record in the table. pH [H3O+] [OH-] Drain cleaner 13 1.00 E-13 1.00E-01 Handsoap 10 1.00E-10 1.00E-04 Blood 7.4 4.00E-08 2.50E-07 Spit 7.4 4.00E-08 2.50E-07 Water 7 1.00E-07 1.00E-07 Milk 6.5 3.20E-07 3.20E-08 Chicken soup 5.8 1.60E-06 6.30E-09 Coffee 5 1.00E-05 1.00E-09 Orange Juice 3.5 3.20E-04 3.20E-11 Soda pop 2.5 3.20E-03 3.20E-12 Vomit 2 1.00E-02 1.00E-12 Battery acid 1 1.00E-01 1.00E-13 Questions 1. What relationship exists between the concentration of the [H3O+], and [OH-]? The relationship exists between the concentration of the [H3O+], and [OH-] is that they multiply by 1.00E-14 2. Does adding water to a solution change the product of the two ions? No. Computer Simulation Activity: Acid-Base Solutions and pH Scale 3. If the solution is acidic, which ion is found in greater concentration? There will be greater concentration of H3O+ Part IV: My Solution 1. Check the ratio box. 2. Slide the Red or Blue sliders up and down and observe what happens to the pH as well as the number of particles represented in the solution? Questions 1. What happens to pH when the red slider increases (goes up)? When the red slider goes up , the pH rises, indicating that the solution has become acidic. 2. What happens to the red particles (acid) when the red slider increases? When the red slider increases, the amount of red particles, and there are nearly no blue particles. 3. What happens to the blue particles (base) when the red slider increases? When the red slider increases, the number of blue particles reduces, until there is just one particle left.