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 another substance. In this activity, your goal is to make up one's mind the molar concentration and strength of two acid solutions by conducting titrations with a base of operations solution of known concentration.

Before we get to the activity, let's take a brief look at how acrid-base titrations work. In that location are three unlike ways to define acids and bases, but for the purposes of this action, we'll employ the Arrhenius definitions. Arrhenius acids are compounds that dissociate when added to h2o, resulting in free hydrogen ions (H⁺) in the water. Arrhenius bases too dissociate when added to water, but these compounds yield free hydroxide (OH⁻) ions in the water. The concentration of hydrogen ions 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 called neutralization. When an acid and a base combine, they produce an aqueous solution with a dissolved table salt made up of the cation from the base and the anion from the acid. For example, a combination of HCl and NaOH volition yield an aqueous solution of sodium chloride co-ordinate to the following equation:

HCl + NaOH → H₂O + NaCl

IMG_1986.JPG

An acid-base titration is substantially a controlled neutralization reaction between i aqueous solution of a known concentration (called a titrant or standard) and one 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 nether a buret containing the titrant. The titrant is so slowly added to the analyte, one drop at a time. If the analyte is an acidic solution, the titrant must exist a basic solution and vice versa in club for the two solutions to neutralize 1 some other.

As the titrant is added to the analyte, the free H⁺ and OH⁻ions in the resulting mixture form 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 (get more bones). If the analyte is a base and the titrant is an acid, the pH of the mixture will decrease (become more than acidic).

IMG_1984.JPG

There are 2 ways to run an experimental titration. 1 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 different 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 bend with a signature S or reverse S shape, as shown below. This curve allows you 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 volition piece of work with in this activity is the kind y'all could collect with a pH meter. Yous could of course upload your own dataset from this activity and compete the activity questions using your own information.

The Dataset

In this activity, you'll analyze data from ii different acid-base titrations. The titrant in both titrations is a 0.50 M sodium hydroxide (NaOH) solution. The analyte in Titration 1 is 25 mL of a hydrochloric acrid (HCl) solution of unknown concentration. The analyte in Titration ii is 25 mL of an acetic acrid (CH3COOH) solution of unknown concentration.

The data for this activity was generated using the ChemReaX acid-base of operations titrations simulator.

The Activity

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

2) Make a graph showing the change in pH over fourth dimension every bit sodium hydroxide is added to each acid solution.

d.png

Click on the Graph tab at the peak of the screen to switch to graph view. Be sure that the Scatter/Box/Bar or Categorical Bubble icon is selected; this will ensure you make a scatter plot. Click the Show buttons beneath the variable names to show the independent variable on the 10-axis and the dependent variable on the Y-centrality of the graph. Be certain each variable is showing on the correct axis. If it's not, you tin can correct that on the panel to the right side of your graph. Side by side, click on the Evidence push button nether the Analyte variable and select the Z axis (on the right side panel). This will show each titration'south data 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) Utilise the graph to approximate 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 gauge concentration of the analyte used in each titration. Show your work.

5) Compare the bodily molarity of the two solutions (which yous volition need to become from your instructor) to your calculated values. What was your percent fault? Show the work you lot did to make up one's mind this.

IMG_1985.JPG

6) Sometimes it's non possible to monitor the exact pH of the analyte-titrant mixture during the unabridged course of a titration considering a pH meter is non available. In these situations, it is still possible to approximate the equivalence indicate of the titration past using a pH indicator solution whose color changes right around the expected equivalence point. The indicate at which the indicator changes color is chosen the endpoint. Depending on the properties of the chosen indicator, the endpoint may or may not closely match the equivalence point. Look at the following chart of indicators and cull the indicator that volition change colour most closely to the equivalence for each of the titrations in this activity. Justify each of your choices.

7) At what volume of added base does pH = pKₐ for the CH₃COOH solution titration represented in this activity?
The Kₐ of CH₃COOH is one.8 ten 10⁻⁵.

AP Chem Extension

eight) Assume you use the aforementioned NaOH solution from this activity to titrate a 20 mL sample of 0.25 M hydrofluoric acrid (HF).
The Kₐ of HF is vi.half-dozen ten 10⁻⁴. Using this information, calculate the following values:

  1. The initial pH of the HF solution

  2. The pH after 5.0 mL of NaOH solution is added

  3. The pH at the equivalence point

  4. The pH after calculation 5.0 mL of NaOH solution beyond the equivalence indicate

*Reply key available to teachers upon asking. info@dataclassroom.com