Experiment 9 volumetric analysis PDF

Preview

Summary

lab report...

Description

Dora Martinez Hernandez CHEM 1111-34

Experiment 9: Volumetric Analysis CHEM 111-34 October 25, 2019 Instructor: Dr. Mahmood Karimi GTA: Brishty Deb Choudhury Dora Martinez Hernandez Lab Partner: Karina Heredia

1

Dora Martinez Hernandez CHEM 1111-34

Objective: To properly use a buret in order to perform a volumetric analysis. To properly prepare the analyte and titrant and observe for a reaction. To calculate the molar concentration of the strong acid used.

Introduction: In this experiment we attempted to perform a chemical analysis using volumetric glassware, this is also known as volumetric analysis. In order to see how the substances, react with each other we first prepared our buret by rinsing it and then filling it up with the titrant, for our experiment we used NaOH. The titrant is the liquid dispensed by the buret into a glass flask that contains analyte. For this experiment we used 25 mL of HCl unknown solution C and applied 2 drops of phenolphthalein into the Erlenmeyer flask, this composed our analyte. We slowly dispense the titrant into the analyte until we achieved a reaction and recorded at what volume of the buret the reaction was produced. We repeated this process 3 times.

2

Dora Martinez Hernandez CHEM 1111-34

Calculation: Volume of acid solution (mL) Buret reading of NaOH, initial (mL) Buret reading of NaOH, final (mL) Volume of NaOH dispensed (mL) Molar concentration of NaOH (mol/L) Moles of NaOH dispensed (mol) Molar concentration of acid solution (mol/L) Average molar concentration of acid solution (mol/L) Standard deviation of molar concentration Relative standard deviation of molar concentration (% RSD)

Trial 1 25.0 mL

Trial 2 25.0 mL

Trial 3 25.0 mL

50 mL

50 mL

50 mL

26.4 mL

33.3 mL

33.5 mL

23.6 mL

16.7 mL

16.5 mL

0.1486 mol/L

0.1486 mol/L

0.1486 mol/L

0.035 mol

0.0025 mol

0.0025 mol

1.4 mol/L

0.099 mol/L

0.098 mol/L

0.53 mol/L 0.49 mol/L

92%

Lab Questions: 4). The mass of KHC8H4O4 is measured to the nearest milligram; however, the volume of water in which it is dissolved is never of concern. water is even added to the wall of the Erlenmeyer flask during the titration. explain why water added to the KHC8H4O4 has no effect on the data, whereas water added to the NaOH solution may drastically affect the data. The moles of KHC8H4O4 are already known so adding water does not affect the moles. NaOH on the other hand will change the concentration and may be diluted. Once it is diluted, we will end up using more solution in order to get a reaction. 5). The wall of the Erlenmeyer flask is occasionally rinsed with water from the flask bottle during the analysis of the acid solution. will this technique result in the molar concentration of the acid solution being reported as too high, too low, or unaffected? Explain. 3

Dora Martinez Hernandez CHEM 1111-34

The amount of water used to rinse the Erlenmeyer flask does not affect the amount of analyte or titrant which is where we are getting our moles from; therefore, it will be unaffected. 6).For the standardization of the NaOH solution in Part A.6, the endpoint was consistently reproduced to a faint pink color. However, the endpoint for the titration of the acid solution in Part B.2 was consistently reproduced to a dark pink color. Will the reported molar concentration of the acid solution be too high, too low, or unaffected by the differences in the colors of the endpoints. Explain. The reported molar concentration will be too low because using too much NaOH will calculate less moles than what is needed, it will also calculate less moles for the acid solution.

Conclusion: For this experiment, in order to perform a volumetric analysis, we prepared a buret and filled it with the titrant (NaOH) and filled an Erlenmeyer flask with our analyte (HCL unknown C and 2 drops of phenolphthalein). For our first trial we slowly dispensed our titrant into the analyte and waited for a reaction. Our group decided to put a white piece of paper under the flask in order to see the light pink shade that would indicate a reaction was about to happen. For our first trial we got a full reaction at 26.4 mL. For our second and third trial we decided to let the titrant dispense at a faster rate until we got to 23 mL and waited for a reaction. For the second trial a reaction was seen at 33.3 mL and for our third trial it was seen at 33.5 mL. For our first trial we first used a pipet to transfer the HCl unknown C solution and therefore we believe contamination affected the reaction observed the first trial. We did not use a pipet for the second and third trial. The results for these trials were very close to each, I believe there was no contamination 4

4...