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    post-lab questions hat are two possible sources of error in the experiment? explain 2. when an acid reacts completely with a base the process is often called neutralization. if the product mixture is neutral, the ph should be 7 at the equivalence point. what is the ph at the equivalence point for the reaction in part i? if it is not equal to 7, explain why. 3. phosphoric acid has three ionizable hydrogens but only two equivalence points were observed. explain why the third equivalence point is not observed.

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    get post-lab questions hat are two possible sources of error in the experiment? explain 2. when an acid reacts completely with a base the process is often called neutralization. if the product mixture is neutral, the ph should be 7 at the equivalence point. what is the ph at the equivalence point for the reaction in part i? if it is not equal to 7, explain why. 3. phosphoric acid has three ionizable hydrogens but only two equivalence points were observed. explain why the third equivalence point is not observed. from EN Bilgi.

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    post-lab questions hat are two possible sources of error in the experiment? explain 2. when an ... the third equivalence point is not observed. (

    post-lab questions hat are two possible sources of error in the experiment? explain 2. when an acid reacts .

    post-lab questions hat are two possible sources of error in the experiment? explain 2. when an acid reacts . 1 Answer

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    Answer to Solved Post-Lab Questions hat are two possible sources of

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    15.6: Acid

    The shape of a titration curve, a plot of pH versus the amount of acid or base added, provides important information about what is occurring in solution during a titration. The shapes of titration …

    15.6: Acid-Base Titration Curves

    Last updated Mar 7, 2021

    15.5: Buffer Solutions

    15.7: Polyprotic Acids

    Learning Objectives

    To calculate the pH at any point in an acid–base titration.

    In an acid–base titration, a buret is used to deliver measured volumes of an acid or a base solution of known concentration (the titrant) to a flask that contains a solution of a base or an acid, respectively, of unknown concentration (the unknown). If the concentration of the titrant is known, then the concentration of the unknown can be determined. The following discussion focuses on the pH changes that occur during an acid–base titration. Plotting the pH of the solution in the flask against the amount of acid or base added produces a titration curve. The shape of the curve provides important information about what is occurring in solution during the titration.

    Titrations of Strong Acids and Bases

    Figure 15.6.1a shows a plot of the pH as 0.20 M HCl is gradually added to 50.00 mL of pure water. The pH of the sample in the flask is initially 7.00 (as expected for pure water), but it drops very rapidly as HCl is added. Eventually the pH becomes constant at 0.70—a point well beyond its value of 1.00 with the addition of 50.0 mL of HCl (0.70 is the pH of 0.20 M HCl). In contrast, when 0.20 M NaOH is added to 50.00 mL of distilled water, the pH (initially 7.00) climbs very rapidly at first but then more gradually, eventually approaching a limit of 13.30 (the pH of 0.20 M NaOH), again well beyond its value of 13.00 with the addition of 50.0 mL of NaOH as shown in Figure 15.6.1b. As you can see from these plots, the titration curve for adding a base is the mirror image of the curve for adding an acid.

    Figure 15.6.1: Solution pH as a Function of the Volume of a Strong Acid or a Strong Base Added to Distilled Water. (a) When 0.20 M HCl is added to 50.0 mL of distilled water, the pH rapidly decreases until it reaches a minimum at the pH of 0.20 M HCl. (b) Conversely, when 0.20 M NaOH is added to 50.0 mL of distilled water, the pH rapidly increases until it reaches a maximum at the pH of 0.20 M NaOH. (CC BY-SA-NC; Anonymous by request)

    Suppose that we now add 0.20 M NaOH to 50.0 mL of a 0.10 M solution of HCl. Because HCl is a strong acid that is completely ionized in water, the initial [H+] is 0.10 M, and the initial pH is 1.00. Adding NaOH decreases the concentration of H+ because of the neutralization reaction (Figure 15.6.2a):

    OH−+H+ −⇀ ↽− H 2 O.

    Thus the pH of the solution increases gradually. Near the equivalence point, however, the point at which the number of moles of base (or acid) added equals the number of moles of acid (or base) originally present in the solution, the pH increases much more rapidly because most of the H+ ions originally present have been consumed. For the titration of a monoprotic strong acid (HCl) with a monobasic strong base (NaOH), we can calculate the volume of base needed to reach the equivalence point from the following relationship:

    molesofbase=(volume)b(molarity)bVbMb=molesofacid=(volume)a(molarity)a=VaMa

    If 0.20 M NaOH is added to 50.0 mL of a 0.10 M solution of HCl, we solve for Vb:

    Vb(0.20Me)=0.025L=25mL

    Figure 15.6.2: The Titration of (a) a Strong Acid with a Strong Base and (b) a Strong Base with a Strong Acid(a) As 0.20 M NaOH is slowly added to 50.0 mL of 0.10 M HCl, the pH increases slowly at first, then increases very rapidly as the equivalence point is approached, and finally increases slowly once more. (b) Conversely, as 0.20 M HCl is slowly added to 50.0 mL of 0.10 M NaOH, the pH decreases slowly at first, then decreases very rapidly as the equivalence point is approached, and finally decreases slowly once more. (CC BY-SA-NC; Anonymous by request)

    At the equivalence point (when 25.0 mL of NaOH solution has been added), the neutralization is complete: only a salt remains in solution (NaCl), and the pH of the solution is 7.00. Adding more NaOH produces a rapid increase in pH, but eventually the pH levels off at a value of about 13.30, the pH of 0.20 M NaOH.

    As shown in Figure 15.6.2b, the titration of 50.0 mL of a 0.10 M solution of NaOH with 0.20 M HCl produces a titration curve that is nearly the mirror image of the titration curve in Figure 15.6.2a. The pH is initially 13.00, and it slowly decreases as HCl is added. As the equivalence point is approached, the pH drops rapidly before leveling off at a value of about 0.70, the pH of 0.20 M HCl.

    The titration of either a strong acid with a strong base or a strong base with a strong acid produces an S-shaped curve. The curve is somewhat asymmetrical because the steady increase in the volume of the solution during the titration causes the solution to become more dilute. Due to the leveling effect, the shape of the curve for a titration involving a strong acid and a strong base depends on only the concentrations of the acid and base, not their identities.

    The shape of the titration curve involving a strong acid and a strong base depends only on their concentrations, not their identities.

    Source : chem.libretexts.org

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