Acid-Base Titration Using a pH Meter
Bradley Holloway and Jennifer Parker
April 16, 2013
In chemistry, the ability to find molarities of acidic and basic solutions is a convenient way to convert between moles of solute and the volumes of their solutions. Through the process of titration, the molarity of these acids and bases can be found to a high level of precision.
To begin titration, one solution is added to a second solution slowly until a certain point where a chemical reaction reaches completion. The titrant (the first solution) is used to titrate the second solution until the reaction is complete. This endpoint is usually marked with an indicator that produces a color. The titrant is a solution with a known molarity in order to determine the molarity of the other. (Clark)
Titration is typically done by filling a buret clamped to a ring stand with solution one and slowly transferring it to solution two in a flask underneath the buret. In solution two, a certain amount of some indicator must be dropped into the flask for the endpoint to be visibly reached. This process would be repeated multiple times to eliminate random error. (Svante)
In this lab the base NaOH will be used to fill the buret and act as the titrant. Then flasks of acetic acid solution will be placed beneath the buret full of NaOH. Then, the base will slowly be added to the solution until the endpoint is reached and the bright pink color fills the liquid inside the container. Once the reaction has reached completion, the process will be repeated. (Tissue)
However in this lab the solution will be monitored with a digital pH meter. A pH meter uses circuitry to determine the concentration of the hydroxide ions in the solution and then converts that to a pH that can be read from a computer. In this lab the pH meter will be hooked up with Vernier’s Logger Pro to collect large amounts of data and easily visualize the titration curve. This titration curve can also be analyzed to determine the pH at which a reaction reached equivalence.
Because this reaction is between a strong base (NaOH) and a weak acid (CH3COOH), the expected equivalence point will be basic. There are multiple ways to determine the actual resulting pH though. The first method is by analyzing the graph to determine the equivalence point and then read the pH level at that x point. a more mathematical method is to determine the molarity of each part of the reaction at the stoichiometric equivalence point, and then to calculate the pH using an equilibrium system with the buffers included. The primary reactions occurring in this scenario are: CH3COOH +H2O <==> H3O+ + CH3COO-
CH3COOH + OH- ==> CH3COO- + H2O
* pH Meter and LabPro
* Ring Stand
* Buret Clamp
* 0.1 M NaOH solution
* Vinegar Sample
* Deionized Water
* Logger Pro
1 Calibrate the pH meter with the standard buffer solution and use attachments to properly set up with Logger Pro on the laptop. 2 Clean and rinse buret and pipet with small portions of NaOH. 3 Fill buret with the provided NaOH sample and record the initial reading. 4 Cautiously pipet 3 mL of vinegar solution into a clean beaker and then add 100 mL of deionized water. 5 Place beaker underneath the buret and make sure the lab setup resembles that of Figure 1. Figure 1:
6 Take pH of initial solution in the beaker and then place 1.00 mL increments of NaOH solution one at a time. Stir with the pH meter and record each individual reading between increments. 7 Continue this procedure until the data reaches five readings beyond the pH of 11.0. 8 Repeat this titration again of a second vinegar sample, but this time when the pH reaches 6, change from increments of 1.00 mL NaOH to 0.01 mL of NaOH until the pH reaches 11.0. 9 Once pH reaches 11.0, take at least five more additional...
Cited: Clark, J. (n.d.). acid-base indicators. chemguide: helping you to understand Chemistry - Main Menu. Retrieved October 8, 2012, from http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html
Svante Arrhenius ' Acid Base Theory. (n.d.). D. W. Brooks Site. Retrieved October 8, 2012, from http://dwb4.unl.edu/Chem/CHEM869R/CHEM869RLinks/www.nidlink.com/7Ejfromm/
Tissue, Brian. Acid-Base Titrations. (2000) Chemistry Hypermedia Project. Retrieved October 8, 2012 from http://www.files.chem.vt.edu/chem-ed/titration/acid-base-titration.html
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