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Learning Aim: Undertake Titration and Calorimetry to Determine Solution Concentration
Objective: To verify the calibration of the equipment required for this learning aim.
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.
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
Fill the burette with distilled water above the 0cm3 line and carefully adjust the water level to exactly 0, where the meniscus aligns.
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Dispense 10cm3 of water into a beaker and record the mass. Repeat this process until 50.0cm3 of water has been used.
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.
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
| 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 |
| 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 |
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 | ||
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.
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.
Calibration and Titration for Solution Concentration. (2024, Jan 14). Retrieved from https://studymoose.com/document/calibration-and-titration-for-solution-concentration
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