New version page

Hunter CHEM 106 - Experiment 11: Acids, Bases and Ka “Where is my Lewis Pair?”

Upgrade to remove ads
Upgrade to remove ads
Unformatted text preview:

Dr. Ali Younes11/5/19Experiment 11: Acids, Bases and Ka “Where is my Lewis Pair?”IntroductionAcids and bases revolve all around us in our daily lives. We may not notice, but some acids and bases are essential and healthy for our bodies, while some can be potentially life threatening. However, determining a strength of an acid or base is something not many people learn. In this experiment, we will be calculating pH of concentrated acids, bases, and salts by determining its Ka value if necessary. We will also analyze a data given by a student who is tryingto identify a weak acid.MaterialsGenral Chemistry Lab Notebook for notesCalculatorObservations and ExperimentalWORK AND EQUATIONS ARE ATTACHED TO THE BACK OF THE LAB REPORTPART 1 Name and concentration of the substancePredict: Acid, base or salt?Calculated pH Acid or base? Nitric Acid 0.00125 MAcid 2.9 acidPotassium hydroxide 0.00133 Mbase 11.13 baseAmmonia 0.00120 Mbase 10.165 baseHydrochlorous acid 0.00128 Macid 5.2 acidSodium Hypochlorite 0.00125 Msalt 9.276 baseAmmonium chloride 0.00142Msalt 6.0498 acidCarbonic Acid 0.00144 Macid 4.6 acidHydrochloric acid 4.55 Macid -0.658 acidPhosphoric Acid0.2 Macid 1.45 acidSodium hydrogen carbonate 0.35 Mbase 8.3 baseBarium hydroxide 0.10 Msalt 13 baseSodium cyanide 0.0510 Mbase 11.015 basePART 2 DATASolution pH [H3O+] ML 0.2M NaOH [A-] eq [HA] eq 1/ [A-] KaA 3.21 6.17*10-45 .01 .04 100 1.54*10-4B 3.66 2.14*10-410 .02 .03 50 1.46*10-4C 4.01 9.77*10-515 .03 .02 33.33 1.47*10-5Discussions and ConclusionPart 1:In part 1, we were given the name and concentration of multiple substances in order to find the pH and to figure out whether it is an acid or a base. In order to find the pH for acids, we had to use –log[H+] in which gives us the value of pH. For pH of bases, we first find the –log[OH-]. Second, we subtract the value from the first step from 14 (14 - (-log[OH-])) in order to find its pH. For weak acids and bases, we must find the Ka or Kb value. We first divide products by reactants, then –log the value we calculate. Then, we must use the ICE table to determine H+ or OH-. For the final step, we must –log the value we receive and that is the answer for acids. Forbases, we must subtract the value from 14.Ka= products/reactants -> stoichiometry -> find x -> X= hydrogen ions for acids X= hydroxide ions for bases. -log(H+)= pH of weak acids, 14 - (-log[OH-]) = pH for weak basesPart 2:In part 2, we were given a data and were asked to create to create a graph and also calculate for Ka. The data on excel was almost identical to the calclulations. ReferencesSmeureanu, G., & Geggier, S. (2019). General Chemistry Laboratory. New York, NY: Lad,Custom Publishing, Inc.Focus Questions1. What is the pH scale?A measuring method with a scale from 0-14 that measures how acidic or basic a solution is.2. How is the pH of a solution calculated? What information is required? How can you tell whether the solution is acidic, basic or neutral?in order to calculate pH, you must use: -log[H+]. The type of solution, acid, base, salt, ion, matters when looking for pH. For weak acids or bases, you must calculate the relevant Ka or Kb values. For strong acids and bases, you must find the –log[H+] for acids and 14 - –log[OH-] Youcan tell the acidity of a solution by knowing: pH>7=base pH=7=neutral pH<7=acid3. What is the Ka for the acid provided in part 2? Identify the acid by the dissociation constant you calculated.The average Ka for the acid provided in part 2 is 1.46x10-4. The acid bye the dissociation constantwould be formic acid (1.8x10-4)Post-lab questions1. What is an acid? Distinguish Arrhenius acids and Bronsted-Lowry acids. Where are they found on the pH scale?An acid can donate protons and form covalent bonds. It is a solution with a pH less than 7. Arrhenius acids are protons (H+). Bronsted-Lowry acids donate hydrogen ions to the base.2. What is a base? Distinguish Arrhenius bases and Bronsted-Lowry bases. Where are they found on the pH scale?A base can accept protons from donators. It is a solution with pH greater than 7. Arrhenius bases always contain OH- while Bronsted-Lowry bases accept hydrogen ions.3. Compare your prediction with your conclusion based on the calculated pH in part 1. Wereany of your results surprising? Why or why not?I predicted some molecules/ions to be salts (Sodium hypochlorite, Ammonium chloride, Barium hydroxide) but I was mistaken. A surprising result was HCl, with a negative pH. Since HCl is a strong acid, I predicted the pH to be extremely low but did not expect it to be negative.4. Lactic acid C3H6O3 is found in sour milk where it is produced by the action of lactobacilli in lactose or the sugar in milk. The pH of a 0.045 M solution of lactic acid was determined using a pH probe and found to be 2.63.a. Calculate the equilibrium constant for this acid.[H+] = 10-pH = 10-.2.63HA = .0023 MKa = [H+][A-]/[HA]Ka = (10-.2.63)2 / (0.023 - 10-.2.63)Ka = 0.00024256109b. Had you not been given the pH of the acid and you had to measure it yourself, how would the method in part 2 be applied to the determination of Ka? would you expect an improvement in theaccuracy of your result with the application of the method of this experiment? Explain why or why not.Since we would measure the pH ourselves, it would be more accurate than the theoretical pH provided. The accuracy of our data would

View Full Document
Download Experiment 11: Acids, Bases and Ka “Where is my Lewis Pair?”
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...

Join to view Experiment 11: Acids, Bases and Ka “Where is my Lewis Pair?” and access 3M+ class-specific study document.

We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Experiment 11: Acids, Bases and Ka “Where is my Lewis Pair?” 2 2 and access 3M+ class-specific study document.


By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?