Acid-Base Titration Lab



Introduction

A titration is a lab technique used to determine the volume of a solution that is needed to react with a given amount of some other substance. In this activity, your goal is to determine the molar concentration and forcefulness of two acid solutions by conducting titrations with a base solution of known concentration.

Earlier we go to the activeness, let'southward take a brief look at how acid-base titrations work. There are three different ways to define acids and bases, but for the purposes of this activity, we'll use the Arrhenius definitions. Arrhenius acids are compounds that dissociate when added to water, resulting in free hydrogen ions (H⁺) in the water. Arrhenius bases also dissociate when added to water, only these compounds yield free hydroxide (OH⁻) ions in the water. The concentration of hydrogen ions tin can be quantified using the pH calibration using the formula pH = -log[H⁺].

When free H⁺ and OH⁻ ions are both available in an aqueous solution, they will combine to make molecules of water (H2O). This is chosen neutralization. When an acid and a base combine, they produce an aqueous solution with a dissolved table salt made upwards of the cation from the base and the anion from the acid. For example, a combination of HCl and NaOH will yield an aqueous solution of sodium chloride according to the post-obit equation:

HCl + NaOH → H₂O + NaCl

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An acrid-base titration is substantially a controlled neutralization reaction between one aqueous solution of a known concentration (called a titrant or standard) and i aqueous solution of an unknown concentration (chosen an analyte). As shown in the experimental setup below, the analyte is placed in a flask and positioned under a buret containing the titrant. The titrant is and then slowly added to the analyte, ane drop at a time. If the analyte is an acidic solution, the titrant must be a bones solution and vice versa in order for the two solutions to neutralize 1 another.

As the titrant is added to the analyte, the free H⁺ and OH⁻ions in the resulting mixture course h2o molecules, and the pH value of the solution changes. If the analyte is an acid and the titrant is a base, the pH of the mixture will increment (become more basic). If the analyte is a base and the titrant is an acrid, the pH of the mixture will subtract (go more acidic).

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There are two ways to run an experimental titration. Ane uses an indicator that changes color based on the pH level of the analyte-titrant mixture. The other uses a pH meter. Each method offers dissimilar information.

Using a pH meter during a titration allows you to determine how the pH level changes as the titrant are added to the analyte. When you plot this data, it generates a titration curve with a signature Due south or reverse S shape, equally shown beneath. This curve allows you lot to identify the equivalence point of the reaction, which is the point at which there are an equal number of moles of acid and base in the mixture. The dataset you will work with in this activity is the kind you lot could collect with a pH meter. You could of grade upload your own dataset from this activity and compete the activity questions using your ain data.

The Dataset

In this activity, y'all'll clarify information from ii different acrid-base titrations. The titrant in both titrations is a 0.fifty M sodium hydroxide (NaOH) solution. The analyte in Titration 1 is 25 mL of a hydrochloric acid (HCl) solution of unknown concentration. The analyte in Titration 2 is 25 mL of an acerb acid (CH3COOH) solution of unknown concentration.

The information for this action was generated using the ChemReaX acid-base titrations simulator.

The Activeness

1) Write balanced neutralization equations for both titrations. Include phase notations.

ii) Make a graph showing the modify in pH over time as sodium hydroxide is added to each acid solution.

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Click on the Graph tab at the meridian of the screen to switch to graph view. Be sure that the Scatter/Box/Bar or Categorical Chimera icon is selected; this will ensure you make a scatter plot. Click the Show buttons beneath the variable names to prove the independent variable on the X-centrality and the dependent variable on the Y-centrality of the graph. Exist certain each variable is showing on the correct axis. If it's not, yous can correct that on the panel to the right side of your graph. Next, click on the Show button under the Analyte variable and select the Z axis (on the right side panel). This will show each titration'southward information with its own color. Finally, check the Connect Dots and Hide Dots boxes.

3) Use the graph to draw the trend in pH over time for each titration.

4) Use the graph to judge the equivalence point for each titration.
Using the volume of NaOH solution that was added to the analyte upon reaching the equivalence point, calculate the approximate concentration of the analyte used in each titration. Show your work.

5) Compare the actual molarity of the two solutions (which you lot volition need to go from your instructor) to your calculated values. What was your percentage fault? Show the work you lot did to determine this.

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6) Sometimes it's not possible to monitor the exact pH of the analyte-titrant mixture during the entire course of a titration because a pH meter is not bachelor. In these situations, information technology is still possible to approximate the equivalence indicate of the titration by using a pH indicator solution whose color changes correct around the expected equivalence point. The bespeak at which the indicator changes color is called the endpoint. Depending on the properties of the chosen indicator, the endpoint may or may not closely friction match the equivalence point. Await at the post-obit chart of indicators and cull the indicator that volition change color most closely to the equivalence for each of the titrations in this activity. Justify each of your choices.

vii) At what volume of added base does pH = pKₐ for the CH₃COOH solution titration represented in this activity?
The Kₐ of CH₃COOH is i.viii x 10⁻⁵.

AP Chem Extension

8) Presume yous employ the same NaOH solution from this activeness to titrate a xx mL sample of 0.25 M hydrofluoric acid (HF).
The Kₐ of HF is 6.6 x 10⁻⁴. Using this data, calculate the following values:

  1. The initial pH of the HF solution

  2. The pH afterward five.0 mL of NaOH solution is added

  3. The pH at the equivalence betoken

  4. The pH later adding 5.0 mL of NaOH solution beyond the equivalence point

*Respond key available to teachers upon request. info@dataclassroom.com