Virtual Experiment 30/31/32

ACID - BASE Equilibrium

The following discussion and videos will show you real titrations and calculations of an acid base titration used to complete the combined Experiment 30/31/32 laboratory assignments.

The assignments that must be completed are:

1. Complete the pre laboratory problems
2. Complete the following parts I through VI for the report using the simulations, virtual labs and class data given.
  1. - Part I - use the pictures of the solutions with indicators added to complete this section
    - Part II -
      1. Use the Virtual Laboratory simulation at http://chemcollective.org/vlab/101, practice the titration of NaOH using a KHP solution and phenolphthalein. Report the molarity of the NaOH solution.
        Use the class data to complete the calculation and average of five trials for the standardization of the NaOH solution.
    - Part III -
      1. Use the video in which the pH of the solutions are measured using a pH electrode and pH paper. Complete the calculations and questions.
        Use the simulation at http://billvining.com/mmlib_sims/#gen_15_2 to determine the pH of several salt solutions.
    - Part IV -
      1. Use the simulation at http://chemcollective.org/vlab/104 to prepare an acetic acid buffer solution
        Use the videos to collect the pH changes to a buffer solution. complete the calculations and questions.
    - Part V -
      1. Use the simulation at http://chemcollective.org/vlab/103 to create a pH plot of the unknown acid being titrated with NaOH and calculate the molarity and the Ka of the unknown acid solution.
    - Part VI -
      1. Use the titration simulation https://www.sciencebysimulation.com/chemreax/AnalyzerAB.aspx to create pH titration curves for a strong acid, weak acid and polyprotic acid titration with NaOH and then a strong base titrated with HCl.
3. Complete the conclusion paragraph for the experiment.

Experiment 30

This lab is a combined laboratory assignment covering the topics in Acid Base Equilibrium. We will be doing parts of this laboratory assignment over the next weeks.

Lab 30.mp4

This video talks about indicators and titrations

Experiment 30

Pre laboratory assignments

Complete the pre laboratory writing assignment in your laboratory notebook. The prewriting must be completed before the laboratory session begins. The writing should include a purpose/hypothesis of the experiment, a discussion or theory, a detailed step by step summary of the procedure explaining what data will be collected and how you will collect it. Data Tables or space to collect the data should be included within the procedure discussion. Look up any SDS on chemicals that you are not familiar.

Attempt the pre laboratory problems.

Lab 31 prelab problems.mp4

This video shows the calculations and theory of the table of compounds in the pre laboratory problems.

notes from April 14 - lab 31 and buffers.pdf

These are scanned notes of the work done for the pre laboratory problems

Procedure

Part I. Indicators

Use the following pictures of the 30 test tubes. To the first column of test tubes, 1 mL of 0.01 M HCl was added. To a last column 1 mL of 0.01 M NaOH was added. To the second, third, and fourth columns, 1 mL of the pH 4, 7 and 10 buffer solutions were added. 5 drops of each indicator solution was then added to each set of test tubes to show how the pH affects the color of the indicator.

Solution

0.01 M HCl
~ pH 2

pH 4 buffer

pH 7 buffer

pH 10 buffer

0.01 M NaOH
~ pH 12

Indicator

phenolphthalein

methyl orange

Bromothymol blue

Methyl red

boiled aqueous red cabbage solution

Universal Indicator

Part II. Standardization of sodium hydroxide solution.

1. Using the Virtual Laboratory simulation at http://chemcollective.org/vlab/101, practice the titration of NaOH using a KHP solution and phenolphthalein. Report the molarity of the NaOH solution.
2. Using the provided class data, choose five trials for the standardization of the NaOH solution. Complete all calculations and questions.

A sodium hydroxide with an approximate 0.2 M concentration will be used to determine the molar mass of an unknown acid in Part III. The sodium hydroxide solution cannot be prepared with a precise determination of the concentration; therefore, the solution must be standardized with a primary standard. A titration will be performed to determine the concentration of the sodium hydroxide solution, accurately. There are several solid acids that could be used as a primary standard for this purpose; however, potassium hydrogen phthalate (KHP) is a very common compound used for this purpose.

Lab 30.mp4

Lab 30

Lab 30 pre lab.mp4

Class Data Sheet for Part II

Calculating the molarity of the NaOH solution from the titration of mass of KHP: https://youtu.be/J8gDdy6y_j8

Lab 12 Part A simulation.mp4

This video is showing the simulation and some of calculations used in the simulation

KHP titration.mp4

In this video, I complete a titration of a known amount of KHP with a solution of NaOH

Part III: pH of Acids, Bases and Salts

We will be measuring and calculating the pH of several acid, base and salt solutions. The first method we will employ is using pH paper to determine the pH for each of the following solutions. Compare the color of the pH paper to color key to determine the estimated pH.

The second method we will employ is the pH meter. After the pH meter has been calibrated with 3 buffer solutions of pH 4, 7 and 10, measure the pH of each solution below using the pH meter. Report the pH of each solution to the nearest 0.1 pH unit.

A video of me completing these two methods is below. Use the video to record the measure pH using the paper and the meter.

pH of solutions using pH paper

Color key of pH paper

0.1 M HCl;
0.1 M NaCl;
0.1 M NH3;
0.1 M NaH2PO4;
0.1 M NaClO

0.01 M HCl;
0.1 M NaOH;
0.1 M NH4Cl;
0.1 M Na2HPO4;
0.1 M C5H5NHCl

0.001 M HCl;
deionized water;
0.1 M (NH4)2C2O4;
0.1 M Na3PO4;
C5H5NHClO

0.1 M HC2H3O2;
tap water;
0.1 M NaC2H3O2;
0.1 M H3PO4

The third method we will employ to measure the pH of several of the salts solutions is a simulation of the Hydrolysis of Salts.

The simulation is available at http://billvining.com/mmlib_sims/#gen_15_2 . The simulation is limited to a few of the salts provided, Measure the pH of the salt solutions above. An older flash version of this simulation is available at http://employees.oneonta.edu/viningwj/sims/hydrolysis_s.html

Experiment 31

This is a presentation of the laboratory assignment. I have worked through many of the reactions for these solutions.

Lab 31 introduction.mp4

This is a video of my lecture introducing this laboratory assignment.

Lab 31 Part 1 pH of solutions.mp4

This is a video of me demonstrating the use of a pH meter connected to the MicroLab system and the measurement of pH of the given solutions using the pH meter and the pH paper.

FlinnScientific

Determine the pH of salt solutions using acid--base indicators. Certain cations or anions in salts react with water to produce H+ or OH-- ions, respectively.

This video is part of the Flinn Scientific Best Practices for Teaching Chemistry Video Series, a collection of over 125 hours of free professional development training for chemistry teachers - http://elearning.flinnsci.com

ATTENTION: This demonstration is intended for and should only be performed by certified science instructors in a safe laboratory/classroom setting.

Part IV. Buffers.

Part A: Work through the simulation of how to prepare a buffer solution at http://chemcollective.org/vlab/104

Part B: In the laboratory assignments, we will prepare a Buffer solution

Prepare a buffer solution using acetic acid and sodium acetate. Calculate the concentration of the acetic acid used in the preparation of the buffer and the concentration of the sodium acetate solution used to prepare the buffer. Determine from these calculations the pH of the buffer solution.

In the laboratory assignment, the pH of water will be measures as we add NaOH or HCl,

We will add 1 M NaOH and 1 M HCl to 25 mL of water by drops and measure the pH of the mixture, then look at how the pH changed with the addition of the NaOH versus the addition of the the HCl.

In the laboratory, we will prepare a buffer solution using acetic acid and sodium acetate and then the pH of buffer solution will be measured as we add NaOH or HCl

We will add 1 M NaOH and 1 M HCl to 25 mL of an acetic buffer solution by 1 mL increments, measuring the pH. We will look at how the pH changes in the buffer solutions versus how it changed in the water.

Buffer Demonstration 2 0 for Avid

Water versus buffer simulation http://employees.oneonta.edu/viningwj/sims/buffer_solutions_s.html

Lab 31 Part 2 Buffer.mp4

Video of pH of water and buffer solution as HCl or NaOH is added.

Part V - Titration of an unknown acid

Use the following virtual simulation to determine the concentration and Ka of an unknown monoprotic acid. http://chemcollective.org/vlab/103

Create a pH plot of the unknown acid being titrated with NaOH. Measure the volume of NaOH added against pH (y axis) from a volume of 0 mL added to a pH of ~12, calculate the molarity of the unknown acid solution)

Use the directions to run the simulation to determine the identity of the unknown acid: https://docs.google.com/document/d/1JHO5HSCHLl9_Ckx0OOE5oIsQxki8cGz_9kFIxNXAYCM

Titration simulation

This simulation http://billvining.com/mmlib_sims/#gen_16_4 can be used to create a titration curve of a strong acid and two weak acids titrated with NaOH.

Experiment 32

titration curves.mp4

An older flash version of a similar laboratory assignment is at http://employees.oneonta.edu/viningwj/sims/titrations_t.html

https://chemdemos.uoregon.edu/demos/Acid-Base-Titration-Computer-Simulation

https://youtu.be/Iruv4YoB3gA

https://virtual.edu.rsc.org/titration/experiment/2

https://www.adobe.com/support/flashplayer/debug_downloads.html

Part VI: pH Titration curves

Use the titration simulation https://www.sciencebysimulation.com/chemreax/AnalyzerAB.aspx to create pH titration curves for a strong acid, weak acid and polyprotic acid titration with NaOH and then a strong base titrated with HCl.

Submit the graphs and the final report.

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