AdeneKolade_101208504_AB Short report_TA-Ethan McCann_2021-11-24

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Acid Base Titration Curves (AB) Date submitted: 11-24-2021 By: Kolade Adene (101208504) Lab section: AW Group: 2 TA: Ethan McCann Procedure: • For the first part of part A of this experiment, the titration of a weak acid (0.100 M HCl) with a strong base (0.100 M HCl), 20ml of the acid was pipetted into a beaker. Then, 10ml of the acid was pipetted into 250ml container using a volumetric pipette. • The acid in the 250ml beaker was diluted to 100ml using distilled water. • Three drops of phenolphthalein were added to the solution in the beaker for titration. • The titration apparatus was set up and the pH probe was calibrated. • The initial volume of the burette and the initial pH of the solution was recorded. • About 2ml of the base was dispensed into the beaker and the new burette reading and pH were recorded. • This process was repeated until approximately 9ml of the base had been dispensed. • The burette tip and sides of the beaker were sprayed using distilled water from a squeeze bottle. The solution in the beaker was observed for any color change. • The base was dispensed in 0.2ml increments until the first sign of pink was observed. • Quarter drops at a time were dispensed while the burette tip and side of the beaker were continuously sprayed down. • This process was carried out until a faint pink colour persisted. The exact volume and pH that the change occurred were recorded. • The titration was continued until a total of 20ml of base was added to the solution and the total volume and pH at each increment were recorded. • For the second part of part A of this experiment, the previous process was repeated using 10ml of acetic acid instead of HCl. • For part B of this experiment, the titration of an antacid tablet with a strong acid (0.100 M HCl), to prepare the antacid tablet, a 250ml beaker was placed on a balance to measure its weight. Next, the crushed antacid tablet was added to the beaker and the total mass was recorded. • Afterwards, 100ml of distilled water was added to the beaker to dissolve the antacid tablet. A magnetic stir bar was placed into the beaker and it was placed on a magnetic stir plate. A pH probe, calibrated with a pH 4 buffer, was submerged just beneath the level of the solution. • 0.5M HCl was used for the burette. No pH indicator was used. The initial volume and initial pH were recorded. • The hydrochloric acid was added in 0.5ml increments until 2ml, then it was added in 1ml increments until a total volume of 24ml was added. • The data obtained was used to plot titration curves using Microsoft excel.

Data and Observations: Part A: Part 1: Titration of a strong acid (0.100 M HCl) with a strong base (0.100 M NaOH) Theoretical concentration of HCl = 0.100 M Volume of HCl used = 10.00 mL Colour change occurred at: 10.80 mL of NaOH, pH 7.28 Volume of NaOH ±0.05(mL) pH 0.00 0.85 2.00 0.98 4.00 1.15 6.00 1.41 8.00 2.20 9.00 2.57 9.20 2.68 9.40 2.85 9.60 3.22 9.80 3.74 10.00 4.42 10.20 4.96 10.40 5.39 10.60 6.85 10.80 7.28 11.00 10.60 12.00 11.74 14.00 12.40 16.00 12.70 18.00 12.85 20.00 12.96 Colour change at Volume 10.80 mL Table 1: Burette readings with corresponding pH values for the titration of a strong acid (0.100 M HCl) with a strong base (0.100 M NaOH)

The volume of NaOH consumed at the equivalence point was 10.8 ±0.05 ml at pH 7.28 Part 2: Titration of a weak acid (0.100 M CH 3 COOH) with a strong base (0.100 M NaOH) Theoretical concentration of acetic acid = 0.100 M Volume of acetic acid used = 10.00 mL Colour change occurred at: 10.60 mL of NaOH, pH 8.30. Volume of NaOH ±0.05(mL) pH 0.00 3.15 2.00 4.14 4.00 4.58 6.00 5.10 8.00 5.56 9.00 5.97 9.20 6.06 9.40 6.16 9.60 6.26 0 2 4 6 8 10 12 14 0 5 10 15 20 25 pH Volume of NaOH added(ml)± 0.10 Titration of stong acid with a strong base Table 2: Burette readings and corresponding pH values for titration of a weak acid (0.100 M CH 3 COOH) with a strong base (0.100 M NaOH) Figure 1: Titration curve of strong acid (0.100 M HCl) and a strong base (0.100 M NaOH).

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9.80 6.42 10.00 6.63 10.20 6.89 10.40 7.14 10.60 8.30 10.80 10.57 11.00 11.46 12.00 12.80 14.00 13.47 16.00 13.75 18.00 13.95 20.00 14.08 Colour change at volume 10.60 mL The volume of NaOH consumed at the equivalence point was 10.6 ±0.05 ml at pH 8.3 0 2 4 6 8 10 12 14 16 0 5 10 15 20 25 pH Volume of NaOH added(ml)± 0.10 Titration of weak acid with a strong base Figure 2: Titration curve of weak acid (0.100 M CH 3 COOH) and a strong base (0.100 M NaOH).

Part B: Antacid tablet (Tums) [stomach acid] = 0.100 mol/L Density ( 𝜌 ) of stomach acid = 1.00 g/mL Volume of 0.500M HCl ±0.05(mL) pH 0.00 9.69 0.50 6.35 1.00 5.96 1.50 5.81 2.00 5.69 4.00 5.42 6.00 5.24 8.00 5.12 10.00 5.02 11.00 4.99 12.00 4.93 14.00 4.83 16.00 4.80 18.00 4.46 19.00 3.40 20.00 2.28 21.00 1.84 22.00 1.70 23.00 1.59 24.00 1.51 Item Mass(g) Empty beaker 101.77± 0.01 Beaker with antacid 103.15± 0.01 Antacid (Tums) 1.38± 0.01 Table 3: Burette readings and corresponding pH values for titration of the antacid tablet.

At the end of the titration of the antacid tablet, the analyte had gone from opaque to translucent. Volume of HCl consumed at 2 nd equivalence point at pH 3.4 = 19 ±0.05 ml Calculations: Part A Part 1 Finding the concentration of HCl using the pH probe The volume of NaOH consumed at the equivalence point is 10.8 ±0.05 ml at pH 7.28 The reaction between NaOH and HCl occurs in a 1:1 mole ratio at the equivalence point, the point with maximum slope in the titration curve. The moles ( ? ) of NaOH added at a concentration ( 𝑐 ) of 0.100 mol/L and a volume ( ? ) at the equivalence point: ? = 𝑐 × ? = 0.100 × 10.8 =1.08mole 0 2 4 6 8 10 12 0 5 10 15 20 25 30 pH Volume of HCl added(ml)± 0.10 Titration of an antacid tablet with a strong acid Figure 3: Titration curve of antacid tablet with a strong acid ( 0.5M HCl).

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Assuming that at this point equal amounts of acid and base have reacted, the number of moles of NaOH will equal the number of moles of HCl ∵ 1:1 reaction =1.08mole . The concentration of HCl used (volume of HCl = 10.00 mL): = ?????? ?? ?𝑎?𝐻 ???????? 𝑎? 𝐸−??𝑖??(??) ×0.100? 10.0?? = 10.8?? ×0.100? 10.0?? =0.108M The relative error of concentration of HCl (theoretical [HCl] = 0.100 M): 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = 𝑒𝑥?𝑒𝑟𝑖?𝑒??𝑎? ?𝑎??𝑒 − ?ℎ𝑒?𝑟𝑒?𝑖𝑐𝑎? ?𝑎??𝑒 ?ℎ𝑒?𝑟𝑒?𝑖𝑐𝑎? ?𝑎??𝑒 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = 0.108 − 0.100 0.100 = 0.0800% Finding the concentration of HCl using the chemical indicator (colour change) The concentration of HCl used (volume of HCl = 10.00 mL): = ?????? ?? ?𝑎?𝐻 𝑎? ?????? ?ℎ𝑎???(??) ×0.100? 10.0?? = 10.8?? ×0.100? 10.0?? =0.108M The relative error of [HCl] using the chemical indicator (theoretical [HCl] = 0.100 M): 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = ?𝑥???𝑖????𝑎? ?𝑎???−?ℎ?????𝑖?𝑎? ?𝑎??? ?ℎ?????𝑖?𝑎? ?𝑎??? 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = 0.108 − 0.100 0.100 = 0.0800% Part 2 Finding the concentration of acetic acid using the pH probe The volume of NaOH consumed at the equivalence point is 10.6 ±0.05 ml at pH 8.3 The reaction between NaOH and acetic acid occurs in a 1:1 mole ratio at the equivalence point. The moles ( ? ) of NaOH added at a concentration ( 𝑐 ) of 0.100 mol/L and a volume ( ? ) at the equivalence point: ? = 𝑐 × ?

= 0.100 × 10.6 =1.06mole Assuming that at this point equal amounts of acid and base have reacted, the number of moles of NaOH will equal the number of moles acetic acid ∵ 1:1 reaction. The concentration of acetic acid used (volume of acetic acid = 10.00 mL): = ?????? ?? ?𝑎?𝐻 ???????? 𝑎? 𝐸−??𝑖??(??) ×0.100? 10.0?? = 10.6?? ×0.100? 10.0?? =0.106M The relative error of concentration of acetic acid (theoretical [Acetic acid] = 0.100 M): 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = 0.106 − 0.100 0.100 = 0.0600% Finding [acetic acid] using the chemical indicator (colour change) The concentration of acetic acid used (volume of acetic acid = 10.00 mL): = ?????? ?? ?𝑎?𝐻 ?????? ?ℎ𝑎???(??) ×0.100? 10.0?? = 10.60?? ×0.100? 10.0?? =0.106M The relative error of concentration of acetic acid (theoretical [Acetic acid] = 0.100 M): 𝑟𝑒?𝑎?𝑖?𝑒 𝑒𝑟𝑟?𝑟 = 0.106 − 0.100 0.100 = 0.0600% Part B Volume of HCl consumed at 2 nd equivalence point= 19.00 ±0.05 ml To calculate the volume of stomach acid neutralized (the concentration of stomach acid is 0.100 mol/L and the concentration of the titrant (HCL) is 0.500 mol/L); = ?????? ?? 𝐻𝐶? ???????? 𝑎? 2?? 𝐸−??𝑖??(??) ×0.500? 0.100? = 19.00?? ×0.500? 0.100? = 95??

The weight of stomach acid that is neutralized by one antacid tablet is (the density of 0.100 M HCl (aq) =1.0 g/mL): ? = ? × 𝜌 = 95?𝐿 × 1.0𝑔/?𝐿 =95g To find out how many times its weight in stomach acid one antacid tablet can neutralize: = ?𝑎?? ?? ????𝑎?ℎ 𝑎?𝑖? ?𝑎?? ?? 𝑎??𝑎?𝑖? = 95 1.38 = 68.84 ∴ one antacid can neutralize approximately 69 times its weight in stomach acid. Discussion: Titration is a sensitive analytical method that helps to determine an unknown concentration of a chemical in solution by introducing a known concentration of another chemical. Several factors can cause errors in titration findings. Indicators are used to determine when a reaction has come to an end (Department of Chemistry, 2021). Misjudging the color of the indicator near the end point is a very common one mistake. Not only is color change sometimes very delicate and slow, but different people have different sensitivity to colors. Even though the volume put down may be just slightly lower or higher than the exact volume at colour change, it can lead to a less accurate result. Using wrong concentrations to begin with, directly affect measurement accuracy. Errors in concentration can occur from chemical decomposition or evaporation of fluids. The solutions may also have been prepared incorrectly or contaminants could have been introduced into the solutions through dirty equipment. In addition, if in the process of cleaning equipment wrong solutions were used, it could affect the concentrations of the solutions to be experimented on, causing less precise results. The accuracy of titration requires precise measurement of the volume of materials in use. Although, markings on a burette can be easily misread. The accurate reading of the liquid level in a burette is at eye level, at the bottom, the flat part of the curve (Department of Chemistry, 2021). This reading, if taken above the meniscus or at any angle other than eye level, can be inaccurate, which results in taking down incorrect readings, and hence, affecting the calculation of the acid concentration. For an indicator whose colour change pH corresponds to a pH on the vertical portion of a titration curve for an acid-base titration, as indicated by the indicator, the end point corresponds to the equivalence point of a titration. The indicator ranges for methyl orange is 3.1-4.4 and that of phenolphthalein is between 8.0 and 9.6 (Department of Chemistry, 2021). For strong acid-strong base titration, any indicator is suitable but for the weak acid-strong base, the neutral range of the methyl orange occurs before the equivalence point, which is approximately at pH 9, is reached so changes colour much too

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soon. Thus, in this experiment phenolphthalein was used as an indicator for both titrations of strong acid-strong base and weak acid-strong base in order to observe colour change that occurs somewhere within the pH range spanned by the steep part of the titration curve. The stronger the antacid, the more acid can be neutralized (Department of Chemistry, 2021). Chemicals contained in antacid are weak bases- strong bases would lead to the risk of damaging the stomach if too much was taken. The antacid used in this experiment is quite effective as it is capable of restoring the stomach pH to near its normal value which is about 1.5 to 3.5 (Burk et al. 2021) and it is also able to neutralize nearly 69 times its weight in stomach acid. Conclusion: The relative error on the calculated HCl concentration by the pH meter was 0.08% while by the indicator it was 0.08%. The calculated CH 3 COOH concentration by the pH meter had a relative error of 0.06% and the calculated CH 3 COOH concentration by the pH meter had a relative error of 0.06%. The antacid tablet analyzed in this experiment proved to be quite efficient.

References: Burk R.C, Azad M., Sun X., Wolf P. A. (2021) CHEM1001 Introductory Chemistry Laboratory Manual. Carleton University Department of Chemistry, 1-6 https://chem.libretexts.org/ https://sciencing.com/errors-titration-experiments-8557973.html