Description

A titration is a common laboratory method used in analytical chemistry to determine the concentration of certain acids or bases during the production of certain biofuels, pharmaceutical drugs, and many other commercial products. In this assignment, you will perform an acid-base titration of an unknown acid.

Instructions

Your task is to conduct an acid-base titration. In this experiment, you will use the simulation from ChemCollective to determine the molar concentration of a weak monoprotic acid using a strong base of known volume and concentration.

Select the link to open the Unknown Acid and Base  simulation in another browser window.

Unknown Acid and Base Problem (chemcollective.org)

Select the File in the upper left corner to open the assignment. Choose Load an Assignment from the drop down list.

In the Assignment list, select Acids and Bases. Scroll down to the Unknown Acid and Base Problem, and select the arrow to the right of the title. This will take you to the lab.

Step 1: Setting Up The Work Bench

Open the simulation on your browser and navigate to the Unknown Acid and Base Problem. The following steps are required to set-up the lab work bench.

In the Stockroom there are three tabs: Solutions, Glassware, and Tools. Select the Solutions tab. In the list of solutions, select the Unknown Acid 0.1 L. This will place 100.00 mL of the unknown acid in an Erlenmeyer flask on the lab workbench. Return to the Stockroom.

  1. In the Solutions list, select Indicators. Choose the Phenolphthalein Indicator Solution from the list. The indicator will turn pink when you have passed the end point. 
  2. Select and hold the bottle of Phenolphthalein and move it over the top of the flask containing the unknown acid. A measurement box will appear. Add 5.00 mL of indicator solution to the flask containing the unknown acid. Right click on the indicator bottle, and choose Remove to take it from the workbench. Return to the Stockroom.

In the Solutions list, choose a Strong Base from the list of solutions. Make note of the type of base, the volume, and the molar concentration. Return to the Stockroom.

In the Glassware list, select Other. from the drop down list, choose the 50.00 mL burette. This will place it on the lab work bench.

Select and hold the flask containing the base, and move it over the top of the burette. A measurement box will appear. Add 50.00 mL of the base to the burette. Record the initial burette reading.

  1. Step 2: Conducting Your Experiment
  2. Select and hold the burette containing the base, and move it over the top of the flask containing the unknown acid. A measurement box will appear. Begin by adding the base to the unknown acid at 5.00 mL increments (watch the pH readings in the panel at the left). Record each increment of base added to the unknown acid, along with the corresponding pH. 
  3. As you approach the colour change, reduce the amount of base to 1.00 mL increments, then 0.50 mL increments. Note: you can use even smaller increments to get more precise results.
  4. Once you have identified the endpoint, repeat the procedure but go past the endpoint. Continue adding base at your selected increment until the pH is approximately 11.
  5. Step 3: Graphing and Analyzing Your Results
  6. Use your data to calculate the concentration (i.e. molar concentration) of the unknown acid.

Graph your titration curve. Place the volume of base on the x-axis and the pH of the unknown acid solution on the y-axis.

Find the equivalence point on your graph, and use the volume at this point to calculate the concentration of the unknown acid. 

  1. When the colour of the solution changes to pink, you have passed the endpoint. However, this gives you a good idea where the endpoint is: it is the volume just before the solution changes colour.

In your discussion, comment on the two ways of calculating the acid concentration. Also include a description of how the number of moles of base affected the pH of the unknown solution.

  • Step 4: Communicating Your Results

Once you have completed your test(s), communicate your results in a lab report.

  1. Your lab report should include the following sections: purpose/objective, materials, procedure, observations, results, discussion, and conclusion. Note: there is no testable question/hypothesis for this experiment. In its place, simply report the purpose or objective of the experiment.

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Assignment: Acid-Base Titration A titration is a common laboratory method used in analytical chemistry to determine the concentration of certain acids or bases during the production of certain biofuels, pharmaceutical drugs, and many other commercial products. In this assignment, you will perform an acid-base titration of an unknown acid. Instructions Your task is to conduct an acid-base titration. In this experiment, you will use the simulation from ChemCollective to determine the molar concentration of a weak monoprotic acid using a strong base of known volume and concentration. Select the link to open the Unknown Acid and Base simulation in another browser window. ChemCollective: Unknown Acid and Base 1. Select the File in the upper left corner to open the assignment. Choose Load an Assignment from the drop down list. 2. In the

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