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Apr 3, 2024

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Experiment 9: (2 weeks) (ABT) Acid/base Titration Purpose The Purpose of part 1 of the acid/base titration lab was to standardize a solution of NaOH; while also focusing on the titrations, curves, endpoints, and the equivalence points. The second part of this lab we explored the acid base relationship to establish an unknown solution. Introduction Titration is a familiar method used to determine the concentration of an unknown solution. A titration is notoriously performed using an acid and a base by adding a predetermined volume of a known solution. Furthermore, an indicator is added to the solution prior to the titration to determine the equivalence point with a change of coloration. Once the equivalence point is reached, the moles of acid are equal to the moles of the base, allowing for precise determination of the unknown acid. Procedure Part I: Monoprotic Acid Please refer to pages 119-120 of First-Year Laboratory Manual: Chemistry 112. 1 Part II: Diprotic Acid Please refer to pages 123-127 of First-Year Laboratory Manual: Chemistry 112. 1 Data and Observations Part I: Monoprotic Acid Trial 1 Trial 2 Trial 3 Mass of weighing container (g) 0.7065 0.6562 0.7056 Mass of container and mass of KHP (g) 1.4750 1.510 1.56 Mass of KHP (g) 0.7685 0.8538 0.8544 Moles of KHP (mol) 0.00376 0.004181 0.004184 Initial Burette Volume (mL) 1.8 0 0 Final Burette Volume (mL) 40.0 42.5 42.5 Total Volume of NaOH added (mL 38.2 42.5 42.5 Concentration of NaOH (M) 0.985 0.984 0.984 Part II: Monoprotic Acid Sample Number of the Acid: #7 Mass of the Unknown Acid: 0.124 g
Colour before the Titration: Light pink, translucent. Colour during the Titration: At pH 7.07, solution slightly green tinted, translucent. 7.07-11.06 colour change range Second Derivative point at which it crosses zero: 37.93mL Figure 1, Volume (mL) vs pH Graph Figure 2, Second Derivative Graph Questions Questions for Part I 1. What is the concentration of the base from the stock bottle? Show any calculations and uncertainty calculations.
? ? = 𝑉 ? 𝐶 ? = 𝑉 ? 𝐶 ? = ? ? Trial 1: Volume NaOH = 38.2 mL = 0.038 L Moles of KHP = 0.00376 mol 𝐶 ? = ? ? 𝑉 ? = 0.00376??? 0.038 ? = 0.0985 ??? ? Trial 2: Volume NaOH= 42.5 mL = 0.0425 L Moles of KHP = 0.004181 mol 𝐶 ? = ? ? 𝑉 ? = 0.004181??? 0.0425 ? = 0.0984 ??? ? Trial 2: Volume NaOH= 42.5 mL = 0.0425 L Moles of KHP = 0.004181 mol 𝐶 ? = ? ? 𝑉 ? = 0.004181??? 0.0425 ? = 0.0984 ??? ? The concentration of NaOH is 0.09835 M Questions for Part II 2. Calculate the molecular weight of the diprotic acid in g/mol using the mass of diprotic acid that you measured in the first step of the procedure and the moles you determined from the titration results (Show all your work). Finding moles of acid (first equivalence): ? ? = 𝐶 ? 𝑉 ? = (0.09835?) ( (0.0367 ?) 2 ) = 0.0018047 ??? Finding molecular: weight: ?? = ? ? ? ? = 0.124𝑔 0.001844??? = 68.71 𝑔 ??? 3. From the following list of five diprotic acids, identify the unknown diprotic acid that you used. Note that not everyone uses the same acid. Diprotic Acid Formula MW Oxalic Acid H 2 C 2 O 4 ·H 2 O 126 Malonic Acid H 2 C 3 H 2 O 4 104 Maleic Acid H 2 C 4 H 2 O 4 116 Malic Acid H 2 C 4 H 4 O 5 134 Tartaric Acid H 2 C 4 H 4 O 6 150 The unknown acid could potentially be Malonic Acid.
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