EXP 1 CHM256 - Experiment 1: Standardisation of Hydrochloric Acid Solution with Sodium Carbonate PDF

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BASIC ANALYTICAL CHEMISTRYCHMLABORATORY REPORTExperiment 1: Standardisation of Hydrochloric Acid Solutionwith Sodium Carbonate Primary StandardPAHANG CAMPUS BRANCHFaculty of Applied SciencesASSHAWN RIZAL BINAHMAD FADZIL2018659262AMIRUL SYAHMI BINAZIZI2018245162MUHAMMAD HAZIQAIMAN BIN AUBAIDELLAH2018...

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PAHANG CAMPUS BRANCH Faculty of Applied Sciences AS120

BASIC ANALYTICAL CHEMISTRY

CHM256

LABORATORY REPORT Experiment 1: Standardisation of Hydrochloric Acid Solution with Sodium Carbonate Primary Standard PREPARED BY

SHAWN RIZAL BIN AHMAD FADZIL 2018659262

AMIRUL SYAHMI BIN AZIZI 2018245162

MUHAMMAD HAZIQ AIMAN BIN AUBAIDELLAH 2018273926

MUHAMMAD ZIL ZAKWAN BIN ZIL HUSHAM 2018406664

AS1204I

PREPARED FOR

SITI NORHAFIZA BINTI MOHD KHAZAAI

Pre-Lab

I

Preparation of Na2CO3 primary standard

II

Preparation of dilute HCl solution

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III

Preparation of Na2CO3 primary standard

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Experiment 1: Standardisation of Hydrochloric Acid Solution with Sodium Carbonate Primary Standard

Objective To determine the exact concentration of a hydrochloric acid solution.

Introduction In analytical chemistry, a standard solution is a solution with a precisely known concentration of a dissolved substance. The precise concentration of an analyte can be known by standardising it with a primary standard solution. Since hydrochloric acid (HCl) used in the experiment is not a primary standard solution, thus, it must be standardised in order to obtain its exact concentration. The suitable candidate for the primary standard reagent to be used in this experiment is sodium carbonate (NaCO3) solution. It is non-hygroscopic and can be prepared easily by dissolving a known amount of pure NaCO3 solid in a fixed volume. In the experiment, the HCl solution and the NaCO3 primary standard solution are prepared via dilution. Once both solutions have been prepared, the dilute HCl solution will be standardised against the NaCO3 primary standard solution through titration. The following reaction ensues:

2 HCl + Na2 CO3 →

2NaCl + H2 O + CO2

Apparatus 100 mL beaker, 100 mL volumetric flask, 250 mL conical flask, 25 mL pipette, burette and retort stand.

Chemicals and Materials Pure sodium carbonate (Na2CO3) solids, concentrated hydrochloric (HCl) acid, distilled water and methyl orange indicator.

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Procedure A. Preparation of Na2CO3 standard solution 1. 0.63 g of Na2CO3 was weighed precisely and the mass was recorded. 2. The Na2CO3 solids were then dissolved into 50 mL of distilled water in a 100 mL beaker. 3. The solution was transferred into a 100 mL volumetric flask and the empty beaker was rinsed thoroughly with distilled water. 4. Distilled water was added into the volumetric flask until the calibration mark and the flask was fitted with a stopper. The flask was shaken and turned upside down four times to ensure the solution is homogenous.

B. Preparation of the dilute HCl solution 1. 20 mL of distilled water was added into a 100 mL beaker and 1.0 mL of concentrated HCl was subsequently added. 2. The acid was diluted until 100 mL with distilled water.

C. Standardisation of the dilute HCl solution 1. A burette was filled with the prepared dilute HCl solution. The initial burette reading was recorded. 2. 25 mL of Na2CO3 standard solution was pipetted into a 250 mL conical flask. Three (3) drops of methyl orange indicator was subsequently added into the flask. 3. The Na2CO3 standard solution in the conical flask was titrated with the dilute HCl solution from the burette slowly whilst shaking the flask until the colour changed from yellow to red. This indicated the end point. The burette reading was recorded. 4. The titration process was repeated twice (2). All data was presented in a table. 5. The exact concentration of the dilute HCl solution was calculated stoichiometrically.

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Results

Data Weight of Na2CO3 used = 0.63 g

Trial

1

2

3

Initial burette reading (mL)

0.0

0.0

0.0

Final burette reading (mL)

30.2

28.0

28.5

Volume of dilute HCl used (mL)

30.2

28.0

28.5

Calculations In the first segment of the experiment, the primary standard solution was prepared by dissolving a precise measured mass of Na2CO3 solids in distilled water. Given that the molecular mass, M of Na2CO3 is 105.99 g/mol, and the mass, m of the solids used in the experiment is 0.63 g, the number of moles, n of Na2CO3 can obtained using the following formula:

Number of moles of Na2 CO3 =

=

Mass of solids Molecular weight of Na2 CO3 0.63 g 105.99 gmol−1

= 5.9×10−3 mol

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The next step involves calculating for the molarity of the Na2CO3 solution. Based on the following formula,

Molarity=

Number of moles of solute Volume of solution

MNa2 CO3 =

5.9×10−3 mol 0.05 L

=0.118 molL−1

Later, the Na2CO3 solution was diluted with 100 mL of distilled water in the volumetric flask. The exact molarity, M2 of the diluted primary standard solution can now be calculated from the volume, V used.

M1 V1 =M2 V2 (0.118)(0.05) =M2 (0.10) M2 =0.059 molL−1

The last segment of the experiment have the diluted HCl solution titrated against the Na2CO3 standard solution. The following reaction took place:

2 HCl + Na2 CO3 →

2NaCl + H2 O + CO2

Based on the equation, 1 mol of Na2CO3 solution reacted with 2 mol of diluted HCl solution standard solution. Hence, stoichiometrically, 0.059 mol of Na2CO3 solution reacted with (2 × 0.059) = 0.118 mol of dilute HCl solution.

Molecule

Ratio Number of moles

Na2CO3

HCl

1

2

0.059

0.059 × 2 = 0.118

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In the experiment, three trials of titration was carried out. The difference between the final and initial burette readings is the actual amount of HCl used in the neutralisation process. From the results, an average value can be obtained.

Average volume of HCl used =

30.2+ 28.0+ 28.5 3

= 28.9 mL

Finally, given that all required data have been found, the molarity of the HCl solution used in the experiment can be calculated.

Molarity of HCl =

=

Number of moles of HCl Average volume of HCl used 0.118 mol 0.0289 L

=4.083 molL−1

Discussion The experiment was conducted to identify the concentration of dilute hydrochloric acid (HCl) solution by standardising it with a primary standard solution. An acid-base titration was carried out after the preparation of the primary standard solution, which is a sodium carbonate (Na2CO3) solution in the experiment and the dilute HCl solution. The preparation of both solutions is based on the dilution technique whilst the titration is based on the principle of neutralisation. The experiment conducted was able to satisfy the objective and can be considered a success. The stoichiometric analysis of the titration reaction shows that the molar concentration of the dilute HCl solution used to neutralise the primary standard solution, Na 2CO3 is 4.083 mol/L. The preparation of the primary standard solution required 0.63 g of pure Na2CO3 solids. A primary standard solution must have several defining characteristics including being highly pure, possessing low reactivity or high stability, and preferably non-hygroscopic. Three trials was carried out for the titration procedure. Each time, a fixed amount of Na2CO3 solution was being titrated by the HCl solution through a burette. The average volume 7

of HCl solution used each time is 28.9 mL. The indicator for the end point in the titration process is signalled by the change in colour of the methyl orange solution. The initial alkaline yellow colour must turn acidic red once the end point is reached. To calculate for the concentration of dilute HCl used in the experiment, several pieces of information is needed to be gathered first. The first step requires the calculation of the molarity of the standard solution, Na2CO3. The molarity of the Na2CO3 standard solution is expressed as the number of moles of its molecule per unit volume. Next, by applying the formula of dilution, where it states that the initial concentrated solution and the final diluted solution are equal in molarity or volume, the molarity of the diluted Na 2CO3 solution can be calculated. This value is then compared to its acid counterpart in the neutralisation reaction by stoichiometry ratios. As seen in the calculations section of this laboratory report, 2 mol of dilute HCl solution is required to react with 1 mol of Na2CO3 primary standard solution, forming a ratio of 2 HCl : 1 Na2CO3. Then finally, the molarity of the dilute HCl solution can be calculated with all the pieces of information obtained. During the experiment, several errors may have affected the results of the experiment. The first possible error may happen when the titration was overdone with excess dilute HCl solution, due to faulty visual end point determination. This form of error is systematic in nature and can alter the results of the data, increasing the deviation from the expected result. The next possible error is a parallax error when the burette readings are misread. This can lead to discrepancies in the results too. The third possible error is the presence of air bubbles in the tip of the burette during the titration process. All of these errors are systematic errors. However, each error can be avoided or lessen by taking several countermeasures. Repeating the titration procedure a few times to obtain an average value can rectify errors related to faulty end point determination. Parallax errors can be avoided by practising appropriate techniques when taking measurements. The eyes must be placed at the centre and perpendicular to the meniscus. Finally, by calibrating the burette before the titration, this can eliminate unnecessary air bubbles and ensure no interference would occur to alter the experimental results.

Conclusion The exact concentration of a hydrochloric acid solution can be determine by standardising it with a primary standard solution such as sodium carbonate solution via titration.

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References

Carpenter, M. E. (2018, March 18). Errors in Titration Experiments. Retrieved from Sciencing: https://sciencing.com/errors-titration-experiments-8557973.html Helmenstine, A. M. (2019, May 7). What Is Titration? Retrieved from ThoughtCo.: https://www.thoughtco.com/titration-definition-602128 Helmenstine, A. M. (2020, February 4). What Is a Primary Standard in Chemistry? Retrieved from ThoughtCo.: https://www.thoughtco.com/definition-of-primary-standard-andexamples-605556 Key, J. A. (2014, September 16). Introductory Chemistry – 1st Canadian Edition. Victoria: BC Campus. Retrieved from https://opentextbc.ca/introductorychemistry/ Moore, J. T. (2011). Chemistry for dummies (2nd ed.). Indianapolis, IN: Wiley Publishing, Inc.

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