CHM256 - PREPARATION AND STANDARDIZATION OF HCl SOLUTION WITH PRIMARY STANDARD Na2CO3 SOLUTION PDF

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PREPARATION AND STANDARDIZATION OF HCl SOLUTION WITH
PRIMARY STANDARD Na2CO3 SOLUTION...

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ANALYTICAL CHEMISTRY

EXPERIMENT 3 PREPARATION AND STANDARDIZATION OF HCl SOLUTION WITH PRIMARY STANDARD Na2CO3 SOLUTION Purpose To learn the technique to prepare an acid solution from a concentrated HCl and to determine the accurate concentration of the HCl solution by standardization with standard solution.

Introduction Hydrochloric acid is a solution of hydrogen chloride (HCl) in water. It is a highly corrosive, strong mineral acid with many industrial uses. Commercially available con HCl is sold as 37-38 % w/w HCl. Since HCl is not a primary standard reagent, the solution of HCl prepared in the lab need to be standardized with a primary standard solution in order to determine its exact concentration. Apparatus 250 mL volumetric flask Retort stand White tile 250 mL conical flask (x3) 25 mL pipette burette

Chemical Reagents Na2CO3 solution (Exp. 2) Concentrated HCl Methyl orange – indicator

Procedure A. Preparation of HCl solution 1. Read the label on the bottle of the concentrated HCl (should be located in the fume hood). From the assay (% w/w, specific gravity and molecular weight) of the concentrated HCl acid given, calculate the molarity of the concentrated HCl and the volume needed to prepare 250 mL 0.1 M of dilute HCl solution. 2. Measure the calculated volume of the concentrated HCl (1) using a 10-mL measuring cylinder and transfer into a 250 mL volumetric flask (which has already contained some distilled water – to dilute conc. acid, add acid to water). 3. Rinse the measuring cylinder and transfer it into the volumetric flask. Then, dilute the acid into the 250 mL of distilled water. Use a stopper to seal the volumetric flask and mix well by turning the flask upside-down a few times in order for the solution to be homogenous.

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B. Standardization of HCl solution 1. 2. 3.

4. 5. 6.

Fill the burette with the prepared diluted HCl and record the initial burette reading. Pipette 25.0 mL of the standard Na2CO3 that you have prepared in Exp. 2 into 250 mL conical flask. Add 2–3 drops of methyl orange as indicator. Titrate the Na2CO3 in the conical flask with the HCl from the burette slowly while shaking the flask until the indicator color changes from yellow to red. Record your reading at the the end point of the titration. Repeat 2–3 times and record all your readings in a table. Calculate the exact molarity of your HCl solution. Transfer the remaining acid solution into a clean reagent bottle KEEP THIS SOLUTION FOR THE NEXT EXPERIMENT (i.e will be used to standardize NaOH solution)

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REPORT SHEET

Experiment No Title

Name Student ID Course Group Date of Experiment Date of Submission Lecturer’s Name

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EXPERIMENT 3 PREPARATION AND STANDARDIZATION OF HCl SOLUTION WITH PRIMARY STANDARD Na₂CO₃ SOLUTION 1.

State the objective of the experiment.

2.

Describe the procedure (in brief). A. Preparation of HCl solution

B. Standardization of HCl solution

.

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3.

Results / Data Obtain the following information from the label on the bottle of the concentrated HCl. Table 1 Molecular Weight of HCl Density @ specific gravity Percent concentration (w/w)% Table 2: Titration of Na2CO3 with HCl Titration Final burette reading Initial burette reading Volume of HCl used

Rough

1

2

3

Average volume of HCl: ......................... Molarity of Na2CO3 (from Experiment 2): ..............................

4.

Questions a) Based on the information in Table 2, calculate the molarity of the conc. HCl solution.

b) What volume of the concentrated HCl is needed to prepare 250 mL 0.1 M HCl solution?

c) Write a balanced equation for the reaction between HCl and Na2CO3.

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d) Using the data above and the stoichiometric ratio from the equation, calculate the exact molarity of the HCl solution.

5.

Conclusion

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