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Standardizing Hcl Against A Standard Solution Of Na2co3 Using Volumetric Analysis Assignment Sample
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Standardizing Hcl Against A Standard Solution Of Na2co3 Using Volumetric Analysis Assignment Sample

Standardizing Hcl Against A Standard Solution Of Na2co3 Using Volumetric Analysis

Introduction

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The aim of the experiment is to analyze the strength of HCl (Hydrochloric acid) in mol/litre by titrating the non-standard solution of HCl against a standard solution of Na2CO3 (Sodium Carbonate). A standard solution of Na2CO3 is prepared and is titrated against a fixed volume of HCl solution using a methyl orange indicator to detect the end point of the reaction. The reaction between hydrochloric acid and sodium carbonate is a neutralization reaction between a strong acid and a strong base. Titrimetric analysis is carried out by the quantitative reaction between the solution of an accurately known concentration or standard solution with a given volume of solution of unknown concentration. The standard solution is called titrant and the solution with unknown concentration is called titrand. The titrant is added from the burette to the titrand until the stoichiometric end point or the equivalence is achieved. The equivalence point and end point for an ideal titration procedure are the same. The equivalence point is the point at which the reaction between the acid and base is complete. And the end point is the appearance of any visible change in the titration process that signifies the completion of the reaction. For the clear detection of the end point, an auxiliary chemical substance called an indicator is added to the reaction medium. Indicators often change color in response to the change in pH occurring in the reaction (Phak et al, 2018). An ideal indicator for a titration reaction will be a chemical species which is a weak acid or base and hence undergoes negligible dissociation in the reaction medium and doesn't get involved in the reaction. Also the chosen indicator should have a pH range desired for the reaction.

Reaction between HCl and Na2CO3:

Na2CO3 (aq) + 2HCl (aq)→ 2NaCl (aq) + CO2 (g) + H2O (l)

Or, CO32- (aq) + 2H+ (aq) → Co2 (aq) + H2O (l)

Methodology

Apparatus & Reagents

  • 2g of Na2CO3
  • 28g of HCl
  • Few drops of methyl orange
  • 50 ml burette
  • Burette stand
  • 10 ml pipette
  • 25 ml conical flask
  • Stirrer
  • White glazed tile

Procedure

  • Preparation of Standard Solution of Na2CO3

According to the stoichiometric reaction 2 mol (0.0189 mol) of HCl reacts with 1 mole of Na2CO3 to complete the neutralization reaction.

 Na2CO3 (aq) + 2HCl (aq)→ 2NaCl (aq) + CO2 (g) + H2O (l)

 Molecular weight of Na2CO3 is 105.988g

Amount of Na2CO3 to prepare 100 ml solution = 2g

 Here, 2g of sodium carbonate is added to 100 ml of distilled water to give approximately

0.2M Na2CO3 solution.

 1 mole of Na2CO3 = 105.988g of Na2CO3 or 105.99g

∴ 2g of Na2CO3 = 2? 105.988 mol = 0.01887 mol or 0.0189 mol

Molarity or Concentration = no of moles of solute? volume of solution in litre

= 0.0189/ 0.1 M = 0.189 M (molar)

  • Preparation of HCl solution

For 1 mole of Na2CO3 we need 2 mol of HCl for the reaction to complete.

Or, 105.988 g of Na2CO3 we need 36.458*2 = 72.916g of HCl

∴ For 2g of Na2CO3 we require 1.28 g of HCl.

Hence, we add 1.25 ml of HCl and dilute it up to 100 ml using distilled or deionised water.

  • Titration Process

Rinse the burette and pipette and the conical flask before adding the required solution. Then fill the burette with the standard solution of Na2CO3 and the burette is fixed on the stand at a proper height. Now, carefully pipette out 10 ml of HCl solution and transfer it to a conical flask. Add a few drops (2-3 drops) of methyl orange indicator to the conical flask (Karki and Thapa 2022). The color of the solution will change to red. Then start the experiment by slowly adding Na2CO3 solution from the burette into the conical flask with constant stirring. The initial reading of the burette to be noted carefully. The Na2CO3 solution is slowly added till the color of the solution turns yellow. At that point the burette opening is closed and the final reading is noted down carefully (Spietz et al, 2019). The lower meniscus reading should be taken for the burette and the pipette. This procedure is repeated for 5-6 times to minimize the error of equipment and other forms of human error.

Figure 1: Schematic diagram of a titration procedure.

(Source: https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classXI/chemistry/kelm206.pdf)

Risk Assessment of possible hazards and minimizing measures

There are several risks ranging from dangerous to careless instances that a student must be wary about while performing the experiment in the laboratory (Kawakubo et al, 2018). The risks, chemical or physical and their preventive measures are described in the table below:

Hazard

Risks

Probability of Occurrence

Control Measures

Effect from the hazard

Broken Lab equipment.

Cuts or Scratches

Likely

Careful disbursement of equipment to students after carefully examining them.

Not intense

Chemicals spilled over floor

Slippery floors lead to serious repercussions to those wearing sandals etc.

Not very likely

Cleaning of the lab on a daily basis.

Intensity may vary, but not life threatening.

Conc. HCl solution.

This is a very vigorous and a dangerous chemical in concentrated quantities, can cause severe burns, allergies, skin disease etc

Pipette out carefully..

Can happen likely

Use of dilute HCl with gloves and masks. Handling conc. HCl with proper guidance from laboratory assistants.

Can cause intense and long term health ailments.

Use of Na2CO3

Na2CO3 is a strong base and hence can cause allergies or irritation if touched with bare hands. Pipette out carefully,

Can happen likely

Na2CO3 should be avoided with bare hands.

Not very intense.

 Table 1: Risk assessment of Hazard

(Source: Self-Created)

Analysis of Results

After completing the experiment the following data is recorded:

Sl. No.

Volume of Na2CO3 used in the reaction.

(cm3)

Initial reading of burette containing HCl.

Final reading of burette containing HCl.

Volume of HCl used in the reaction.

(cm3)

1.

10

50

45.8

4.2

2.

10

45.8

41.8

4.0

3.

10

41.8

37.5

4.3

4.

10

37.5

33.4

4.1

5.

10

33.4

29.4

4.0

6.

10

29.4

25.4

4.0

Table 2: Observation table for the experiment

(Source: Self-Created)

Calculation of Strength or Concentration of HCl

The mean value for the volume of HCL used in the neutralization reaction will be

 = 4.2+4.0+4.3+4.1+4.0+4.0/6 cm3

 = 4.1 cm3 or ml

 = 4.1/1000 L

 = 0.0041 L

Molarity of Na2CO3 =0.1887006 mol/L

Volume of Na2CO3 used = 10 cc = 0.01L

Volume of HCl used = 4.1 cc = 0.0041 L

At the end point of the reaction, an equilibrium is established between the titrant and the titrand. Hence, the equation aM1V1= bM2V2 can be applied to the

reaction mixture.

Here,

a,b are the number of moles of HCl and Na2CO3 required to complete the reaction.

M1 and M2 indicate the molar concentration of HCl and Na2CO3 respectively.

And, V1V2 indicates the molar volume of HCl and Na2CO3 respectively.

∴ aM1V1= bM2V2 implies,

 2*M1*0.0041L = 0.188706 mpl/L * 0.01L

M1 = 0.9204 9 mol/L

= 0.921 mol/L

Background of the Experiment

According to the Bronsted-Lowry concept of acids and bases, a species is considered to be an acid if it has a tendency to lose H+ ion, while a base has a tendency to accept H+ ion (Kwon et al, 2019). During an acid-base reaction, acid loses a proton to form a conjugate base and a base accepts a proton to form a conjugate acid (Yadav et al, 2020). Here, HCl loses protons immediately and Cl- is a weak base, thereby HCl is a strong acid. However Na2CO3 is considered to be a weak base.

Titration Curve of the Reaction

A titration curve for a reaction is a graph plotted for the reaction with the change in pH of the analyte in one axis versus the change in volume of the titrant (Bismark et al, 2021). In this experiment, as the reaction proceeds the pH of the HCl solution, initially below 3.0 (highly acidic) , starts increasing gradually with the addition of Na2CO3. The graph is plotted below:

Figure 2: Titration Curve For Titration of HCl and Na2CO3

(Source: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.chemistryscl.com%2Fadvancedlevel%2Fphysical%2FNaOH-and-HCl-titration-curve%2Findex.php&psig=AOvVaw2mFXb2htroazrDXLABHe0n&ust=1650100689098000&source=images&cd=vfe&ved=0CAwQjRxqFwoTCKj3qKbelfcCFQAAAAAdAAAAABAJ )

Point 1 is the initial phase of the reaction. The pH is low or acidic and the concentration of H+ ions is high in the solution.

HCl (aq) + H2O(aq) → H3O+  + Cl-

Point 2 determines the equivalence point of the reaction. pH of the solution is 7. Neutralization is complete.

 Na2CO3 (aq) + 2HCl (aq)→ 2NaCl (aq) + CO2 (g) + H2O (l)

Point 3 With the addition of further Na2CO3 to the solution, the concentration of the OH- ions increases and the solution becomes basic.

Choice of Indicator

Methyl orange is chosen as the indicator, as its pH range matches the reaction specifically i.e. 3.1 (red) to 4.4 (yellow) (Fithri et al, 2019). And being a weak base it can not compete with Na2CO3 for the proton and hence can’t interfere in the reaction.

Figure 3: Physical & Chemical structure of Methyl Orange

(Source: https://www.carlroth.com/medias/T118-SF-1000Wx1000H?context=bWFzdGVyfGltYWdlc3wzMzA0M3xpbWFnZS9qcGVnfGltYWdlcy9oNmMvaDhiLzg5NDAyNTM5MDQ5MjYuanBnfDU3OGUyZTQzNmFiMjJiMjRmODQ5Y2YwNDcwNzVhZTljNTE3MjZlOTY4OTg2MDU2ZTg4ODFiMDNhZDIyYzRmMTg)

Errors

Errors in this experimental method can be both physical i.e due to the equipment or the human error of taking the burette readings or the pipette reading.

Result

The result of the experiment to determine the concentration of HCl solution by titrating it against the standard solution of Na2CO3 is found to be 0.921 mol/L.

Reference List

Journals

Bismark, O., Michael, O.K., Justice, O.K., Otoo, E., Eyram, N. and Benjamin, K.D., 2021. Dextrose Equivalent Analysis of Acid Hydrolysed Corn and Cassava Starch Sourced from Ghana. Science, 9(2), pp.45-53.

Fithri, N.A., Fitrya, F., Shabrina, T. and Yulanri, D., 2019. Antioxidant activity analysis and standardization of Parkia speciosa (Petai) pods ethanol extract. Science and Technology Indonesia, 4(1), pp.5-10.

Karki, D. and Thapa, Y.N., 2022. Assessing Physico-Chemical Parameters of Drinking Water in Majkhola, Tansen, Palpa. International Journal of Applied Sciences and Biotechnology, 10(1), pp.60-70.

Kawakubo, S., Omori, T., Suzuki, Y. and Ueta, I., 2018. Droplet-counting microtitration system for precise on-site analysis. Analytical Sciences, 34(2), pp.243-247.

Kwon, D.A., Kim, Y.S., Baek, S.H., Kim, S.K., Kim, H.K., Jo, S.K., Jung, U., Park, H.R. and Lee, H.S., 2019. Protective effects of a standardized extract (HemoHIM) using indomethacin-and ethanol/HCl-induced gastric mucosal injury models. Pharmaceutical biology, 57(1), pp.543-549.

Phak, C.Z., Saleh, S.B.M. and Muzammil, M.A., 2018, December. Comparison of Total Inorganic Carbon (TIC) Analysis with Titration Method Analysis in Determining Carbon Dioxide (CO2) Content of Amine Solvent. In IOP Conference Series: Materials Science and Engineering (Vol. 458, No. 1, p. 012033). IOP Publishing.

Spietz, T., Chwo?a, T., Jastrz?b, K., Dobras, S. and Wilk, A., 2019. Laboratory studies of ammonia emissions from the CO2 capture process using aqueous ammonia from the Solvay Process. Polish Journal of Environmental Studies, 28(4), pp.2835-2843.

Tonu, N.T., Mahiuddin, M.D. and Dutta, A.K., 2020. Comparative study on the Physico-chemical and antibacterial characteristics of Tamarindus indica and Momordica charantia seed lipid. IJCS, 8(2), pp.1968-1972.

Yadav, R.B., Kumar, B., Vats, A., Singh, S.N., Pathak, D.P. and Arora, R., 2020. Development, standardization and validation of analytical method for quality assurance and quality control of aloe-based pharmaceuticals and nutraceuticals. Trakia Journal of Sciences, 18(4), p.295.

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