Calibration and Titration for Solution Concentration

Introduction

Learning Aim: Undertake Titration and Calorimetry to Determine Solution Concentration

Objective: To verify the calibration of the equipment required for this learning aim.

Methodology

Calibration of Equipment

Balance

Firstly, ensure the balance remains at zero when started, ensuring precision. Place it on a stable and flat surface, preferably on the front bench to minimize vibrations. Wipe the balance with a cotton cloth to remove any dust. Finally, calibrate the balance three times with 1g, 5g, 10g, and 20g masses.

Calibration Masses (grams)	1st	2nd	3rd	Mean	% Error
1.000	1.000	1.000	1.000	1.000	0.00
2.000	2.000	2.000	2.000	2.000	0.00
5.000	5.011	5.011	5.000	5.000	0.00
10.001	10.020	10.020	10.020	10.020	0.19
20.003	20.040	20.040	20.040	20.040	0.18

The balance was correctly calibrated three times with 1g, 2g, 5g, 10g, and 20g masses to ensure its suitability for a range of masses.

Pipette

Start by recording the temperature and filling a beaker with 150cm³ of distilled water. Fill the pipette with 25.0cm³ of distilled water, ensuring the meniscus is aligned with the marked line. Transfer the water to an empty beaker that has been zeroed on the scale. Empty the beaker and recalibrate the balance for repeated measurements.

Sample	Display Mass (grams)	Displayed Temperature
1	24.593	23.6
2	24.906	24.0
3	24.045	24.1
Mean Mass	24.848	23.9

Temperature of water: 23.9 degrees Celsius

Density of water at 23.9°C: 0.99756g/cm³ [CRC 97th edition]

Expected mass of 25cm³: 25 * 0.99756 = 24.939g

Burette

Fill the burette with distilled water above the 0cm³ line and carefully adjust the water level to exactly 0, where the meniscus aligns. Dispense 10cm³ of water into a beaker and record the mass. Repeat this process until 50.0cm³ of water has been used.

pH Meter

Thoroughly rinse the pH probe with distilled water and immerse it in the first buffer solution.

Set the display to pH 3 and record the reading. Repeat this process with pH 7 and 9 after rinsing the probe with distilled water.

pH	Reading 1	Reading 2	Reading 3	Mean
pH 3	18.640	18.624	18.624	18.629
pH 7	33.344	33.344	33.388	33.358
pH 9	40.544	40.560	40.528	40.544

Problems with the pH probe:

At all times, ensure the pH probe is stored in a moist environment to prevent drying out, which could require replacement. Additionally, storing the pH probe in pH 4 solution prevents buildup and contamination, ensuring accurate readings. Start with the highest pH solution to avoid probe diffusion. Rinse the pH probe between measurements to prevent solution contamination.

Preparing Standard Solution

Equipment Required:

• Weighing Boat
• Anhydrous Sodium Carbonate
• Distilled Water
• Weighing Balance
• Stirring Rod
• Beaker
• Volumetric Flask

Method:

1. Record the mass of the empty weighing boat and calibrate the scale.

2. Carefully weigh between 1.25-1.45g of anhydrous sodium carbonate into the weighing boat.

3. Pour the sodium carbonate from the weighing boat into a beaker.

4. Re-weigh the weighing boat after transferring the sodium carbonate to the beaker.

5. Add 150cm³ of distilled water to the beaker with sodium carbonate and stir thoroughly.

6. Once fully dissolved, transfer the solution to a volumetric flask, rinsing the beaker and stirrer with distilled water to prevent wastage.

7. Fill the 250 cm³ volumetric flask with distilled water until the meniscus reaches the 250cm³ line.

8. Rinse the volumetric flask several times to ensure proper mixing.

Mass of Boat (Empty)	Mass with Sodium Carbonate	Mass after Transfer	Amount of Sodium Carbonate in Solution	Mol dm-3
0.928g	2.315g	0.924g	1.387g	0.052

To use the solution for standardizing HCL, determine the number of moles of sodium carbonate in the solution:

The formula mass (Mr) of sodium carbonate in the solution is (23*2) + 12 + (16*3) = 106

The number of moles of sodium carbonate = 1.387g / 106 = 0.01309

Concentration = 0.01309 / 250 * 10^-3 = 0.052 mol dm^-3

Risk Assessment

Hazard	Risk	Precaution
Sodium Carbonate	Irritation to skin and eyes	Wear goggles and gloves; avoid skin contact
Glass Equipment	Potential for breakage and injury	Handle with great care
HCL Solution	Corrosive to human tissue	Wear lab coat and goggles; rinse thoroughly if in contact with eyes or mouth

Titrating Hydrochloric Acid - Determining HCL Concentration

Equipment Used:

• Pipette (25cm³)
• Burette (50cm³)
• Volumetric Flask
• Pipette Filler
• Beaker
• Sodium Carbonate Solution
• Phenolphthalein Solution
• Clamp Stand
• HCL

Risk Assessment

Hazard	Risk	Precaution
Glass Equipment	Potential for breakage and injury	Handle with great care
HCL Solution	Corrosive to human tissue	Wear lab coat and goggles; rinse thoroughly if in contact with eyes or mouth

Method:

1. Rinse the burette with HCL and fill it up until the meniscus rests at 0.00.

2. Pipette 25cm³ of the 0.053 mol dm^-3 anhydrous sodium carbonate into a conical flask and add 3 drops of phenolphthalein indicator.

3. Slowly add the HCL, observing for a color change from pink to colorless.

4. Continuously swirl the flask to ensure proper mixing and record the volume for this trial titration.

5. Refill the burette with 25cm³ and adjust it to 0.00.

6. Repeat steps 2-4 using a new conical flask and 25cm³ of the same sodium carbonate solution, adding 3 drops of phenolphthalein.

7. Record the HCL volume when the color changes from pink to colorless.

8. Repeat the steps for additional trials until you have 2 or more concordant results.

Trial	Rough	1st	2nd	3rd	4th
Initial Volume (cm3)	0.00	14.25	26.50	0.00	13.45
Final Volume (cm3)	14.25	26.40	39.90	13.45	26.95
Volume of HCL Used (cm3)	14.25	12.15	13.40	13.45	13.50
Average Volume of HCL Used (cm3)	13.40 13.45 13.50 = 89.853
Mean Titre of HCL	13.45 * 10-3 dm3

Equation for the reaction:

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

Ratio: 1 mole of sodium carbonate reacts with 2 moles of hydrochloric acid.

Substance	Na2CO3	HCl	Ratio
Volume (cm3)	25 * 10-3	13.45 * 10-3
Concentration (mol dm-3)	0.052	x
Number of Moles (Concentration * Volume)	1.3 * 10-3	13.45x * 10-3
13.45x * 10-3 = 2 * 1.3 * 10-3	x = 2 * 1.3 * 10-3 / 13.45 * 10-3
Concentration of HCl (mol dm-3)	0.1933

Evaluation:

Throughout this experiment, a pipette was used instead of a measuring cylinder to ensure accuracy, as the pipette's precision is comparable. Using slightly different volumes of alkali could introduce structural errors, which the pipette minimizes by delivering the same volume of acid consistently.

To obtain accurate results, measurements were taken at the meniscus's end. Additionally, acid was added drop by drop, and the flask was swirled continuously to ensure thorough mixing. Overall, the titration process improved confidence over the course of the experiment.

Conclusion

In conclusion, this experiment successfully calibrated various equipment and performed titrations to determine the concentration of hydrochloric acid (HCl) solution. The calibration of the balance, pipette, burette, and pH meter ensured the accuracy and reliability of measurements throughout the experiment.

The preparation of the standard solution of sodium carbonate allowed for the determination of its concentration, which was crucial for subsequent titrations. The calculated concentration of the sodium carbonate solution was found to be 0.052 mol dm^-3.

Titrating the sodium carbonate solution with hydrochloric acid provided consistent results, with an average titre of 13.45 * 10^-3 dm³ and a calculated concentration of HCl at 0.1933 mol dm^-3.

This experiment highlighted the importance of precise calibration and careful laboratory techniques in analytical chemistry. The acquired results demonstrate the proficiency in performing titrations and accurately determining solution concentrations.