Anachem-Lab-M8 Activity 2 - Lab PDF

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Expt. 1 Preparation and Use of BuretExperimental DataInstruction: Using a 25-mL glass stoppered buret filled with distilled water and with an initial reading (IR) of 0 mL, if about 1/3 of the content is run down, record the final reading (FR) for Trial 1. For trial 2 run down another 1/3 of the rema...

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Expt. 1 Preparation and Use of Buret Experimental Data Instruction: 1. Using a 25-mL glass stoppered buret filled with distilled water and with an initial reading (IR) of 0.00 mL, if about 1/3 of the content is run down, record the final reading (FR) for Trial 1. For trial 2 run down another 1/3 of the remaining content. Record the IR and FR of the second trial. 2. Using a 25-mL rubber stopper buret filled with distilled water and with an initial reading (IR) of 0.00 mL, if about 1/4 of the content is run down, record the final reading (FR) for Trial 1. For trial 2 run down another 1/4 of the remaining content. Record the IR and FR of the second trial. 3. Complete the table.

A. Buret with Glass Stopper TRIAL 1

TRIAL 2

Final reading

8.33 mL

13.89 mL

Initial reading

0.00 mL

8.33 mL

Volume of H2O released

8.33 mL

5.56 mL

B. Buret with Rubber Stopper TRIAL 1

TRIAL 2

Final reading

6.25 mL

10.94 mL

Initial reading

0.00 mL

6.25 mL

Volume of H2O released

6.25 mL

4.69 mL

D. Guide Questions 1. Basically, when is glass stoppered buret used? Glass stoppered buret or acid buret is commonly used for accurately measuring small volumes of liquid. It measures liquids such as acid that cannot be measured by the rubber stoppered buret because it will erode. When is rubber stoppered buret used?

A rubber stoppered buret or alkali buret is used to measure the basic liquid that will destroy the glass stoppered buret if it was used to measure it. When is a PTFE buret used? A buret with a PTFE stopcock is one of the most commonly used buret today. It can be used to measure any titrant. 2. Describe the recommended method for the manipulation of a buret stopcock during titration. The recommended way for the manipulation of a buret stopcock during titration is to face the buret with its stopcock on the right and manipulate it using your left hand. Your thumb and forefinger or middle finger should be wrapped around to turn the stopcock as slight inward pressure is applied and then your last two fingers should be slightly pushing against the tip of the buret to be able to absorb the inward pressure. 3. Why is it necessary to completely fill the rubber tubing of the stopcock with the solution before titration? It is necessary to completely fill the rubber tubing of the stopcock with the solution before titration to avoid air bubbles. Air bubbles can exist between the gaps if it is not filled completely and the existence of air bubbles can lead to errors. 4. Describe the proper way of cleaning the buret. The accuracy of titration is determined by the titrant flowing into the flask and not clinging to the burette walls. It is a standard laboratory practice to rinse the burette thoroughly with deionized water then with a small amount of titrant. After each rinse, open the stopcock to let the liquid to drain at the bottom; if there is a lot of liquid adhering to the burette's walls, properly clean it and repeat the rinse process. Expt. 2 Preparation and Standardization of Solutions for Acidimetry and Alkalimetry The following data were obtained by a group of students in Analytical Chem. A. Standardization of prepared NaOH solution Data & Results: Complete the table. TRIAL 1 Wt. of KHP (MM 204.22 g/mol)

TRIAL 2

TRIAL 3

0.3580 g

0.3650 g

0.3600 g

Final Reading

7.50 mL

14.70 mL

22.00 mL

Initial Reading

0.00 mL

7.50 mL

14.70 mL

Total vol. of NaOH used

7.50 mL

7.20 mL

7.30 mL

Titration Data

Std. Concn . of NaOH, (N)

0.2337 N or eq/L

0.2482 N or eq/L

Ave. Std. Concn. of NaOH

0.2415 N or eq/L

0.2411 N

B. Standardization of the prepared HCl solution Data & Results: Complete the table. TRIAL 1 Vol. of HCl used

TRIAL 2

TRIAL 3

20.00 mL

20.00 mL

20.00 mL

Final Reading

19.00

18.80

19.20

Initial Reading

0.00 mL

0.00 mL

0.00 mL

19.00 mL

18.80 mL

19.20 mL

0.2266 N or eq/L

0.2315 N or eq/L

Titration Data

Total vol. of NaOH used Std. Concn . of HCl (N) Ave. Std. Concn. of HCl

0.2290 N or eq/L

0.2290 N or eq/L

NOTE: All weight readings from analytical balance must be expressed up to 4 decimal places. All volume readings must be expressed up to 2 decimal places. Guide Questions 1. Give the general directions for the use of volumetric flask in the preparation of accurate volume solution. General directions for the use of volumetric flask: - Add your solute to your solution. - Add enough solvent to dissolve the solute. - Keep adding your solvent until it gets close to the line marked on the volumetric flask. - Use a pipette to fill the flask. - Use the meniscus of the solution and the graduation line on the flask to determine your endpoint. - Place the volumetric flask stopper into the volumetric flask to seal it. - Invert the flask to mix the solution thoroughly.

2.

Write the equation showing how to determine the calculated concentration of NaOH: - N of NaOH = g KHP Eq Wt. KHP x V NaOH of HCl: -

N of HCl = N NaOH x V NaOH V HCl

3.

What is the appropriate indicator in the titration of a strong acid with a strong base? phenolphthalein of a weak acid with a strong base? - phenolphthalein

4.

How do you differentiate the method of standardizing the NaOH solution from that of HCl solution? - The NaOH solution is standardized using KHP or Potassium acid phthalate as the primary standard. In contrast, the HCl solution is standardized using a standard secondary substance which is then prepared NaOH solution, which has been standardized.

5.

What is a primary standard substance? A primary standard is defined as a highly purified compound that serves as a reference material in all volumetric and mass titrimetric methods. Important requirements for a primary standard are: − 1.High purity (established methods for confirming purity should be available) − 2. Atmospheric stability − 3. Absence of hydrate water so that the composition of the solid does not change with variations in relative humidity − 4. Ready availability at modest cost − 5. Reasonable solubility in the titration medium − 6. Reasonably large molar mass so that the relative error associated with weighing the standard is minimized...