Standardizing Hcl Against Standard Solution Of Na2co3 Using Volumetric Analysis

Pages: 11 Words: 2806

Standardizing Hcl Against A Standard Solution Of Na₂co₃Using Volumetric Analysis

Introduction

Get Free Samples Written by our Top-Notch Subject Experts For Taking Online Assignment Help Services

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, CO₃^2-(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 Na₂CO₃used = 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.

M₁and M₂indicate the molar concentration of HCl and Na₂CO₃ respectively.

And, V₁V₂indicates 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</>.<>
</>

<>References</>

<>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.