ph titration and ph

The primary goal of this lab was to establish pH and pH titrations. This lab was divided into two parts, A and B. Different pH values were obtained for various solutions in Part A. Similarly, part B entailed determining the weight, mass, and pH values of benzoic acid for samples 1 and 2. The molecular weight was then estimated using a graph of pH versus NaOH length. The first and second corresponding points were 15.2 mL and 32.2 mL, respectively. In particular, this lab is essential to many scientist and engineers. A pH and pH titration is an exercise conducted with the aim of determining the concentration of unknown base or acid (Jo, 2003). Here, a titrant’s certain amount of known concentration is added to neutralize unknown concentration as it reaches the equivalence point. Partially, a weak monoprotic acid is ionized in water solution.

Eq.1

The ionization constant, Ka = [H3O+] [A-]/ [HA]

Eq.2

Also, pKa = pH – log [A-] + log [HA]

Eq.3

The half equivalent point is given as pH = pKa

The next section of the report explores material and methods. Moreover, the paper touches on the results and discussions, as well as the post-lab questions before coming to its conclusion. In addition to the reference section, acknowledgment and other supplementary information are included right after the conclusion (Jo, 2003).

Material and Methods

Various apparatuses were assembled for the preparation of the lab. The equipment included an empty beaker, burets, and benzoic acid. Subsequently, a graph of pH versus NaOH solution’s volume added was plotted to determine the equivalence point. Moreover, Ka was calculated for the benzoic acid from the measurement. Mass of the benzoic acid for sample one = 49.4-49.1 = 0.30g. For sample two, the mass = 52.6-52.3 = 0.3g.

Results and Discussion

Table 1: Part A

Solution

pH

0.015M HCl

2.10

0.06 M HOAC

2.98

0.022 M NaOH

11.93

0.1 M NH4Cl

5.45

0.1M NaOAC

7.42

0.015M NH4Cl

5.77

0.02 M NH3

10.80

0.04 MNaOAC

8.30

Table 2: Part B

Sample

Beaker mass

Weight

pH

Acid

Beaker mass plus benzoic acid

1

49.1 g

0.3 g

3.30

Benzoic acid

49.4 g

2

52.3 g

0.3 g

3.11

Benzoic acid

52.6 g

Figure 1: A Graph of pH versus NaOH Added

In part A, it is noted that various solutions present different values of pH. For example, 0.015M HCl has a pH of 2.10. Conversely, 0.02 M NH3 has a pH of 10.8. In the same way, different samples in part B produces different values of pH. When a graph is drawn, it is evident that there are two equivalent points. The first equivalent point occurs at 15.2mL while the second one at 32.2mL.

H2C4O4 = O4 + H2 + H2 + C4 = (1.008g x 4) + (12.01g x 4) + (16g x 4) = 116.10 grams

Therefore, the percentage error = (actual value – calculated value)/ actual value

= (116.10 – 118.80)/ 116.10 x 100 = 2.33%.

Post Lab Questions

a). It is not possible since HCl dissociates in water because it is a strong acid.

b) It is possible to monitor the acid’s Ka from the graph. For this reason, the graphical method is the easiest method for getting the Ka of the acid.

c) From the graph, the mass of the molar weight that would have been obtained from the benzoic acid = 118.80 grams.

d) Table 3: The Measurement and the Uncertainty

Measurement

Uncertainty

Calculation of the uncertainty

118.80

2.70

(116.10 – 118.80)/ 116.10 x 100 = 2.33%.

Conclusion

This lab accomplished its objective of determining the pH and the pH titrations. Various equipment was used for the success of the lab even though a slight error (2.33%) was recorded. Possibly, such errors are minimized by using the effective equipment.

Acknowledgement

I am taking this kind of opportunity to acknowledge my university and the department of chemistry in particular for making this lab successful. My highest appreciation also goes to my professor for making this course friendlier.

Reference

Jo, K. (2003). Continuous on-line feedback based flow titrations. Complexometric titrations of calcium and magnesium. Talanta, 60(1), 131-137. http://dx.doi.org/10.1016/s0039-9140(03)00114-0

Supplementary Information

Table 4: Raw Data of Part A

Table 4: Raw Data of Part B