Preparation of Ammonium Acetate Buffer (pH 6.8)

1. Required Materials
1. ** Ammonium Acetate **: Analytical purity level to ensure that its purity meets the experimental requirements to ensure the quality of the buffer.
2. ** Glacial Acetic Acid **: Also analytically pure, used to adjust the pH value of the buffer.
3. ** Distilled Water **: High purity distilled water is required to avoid impurities in the water from affecting the properties of the buffer.
4. ** Electronic Balance **: Used to accurately weigh the quality of ammonium acetate.
5. ** pH Meter **: Accurately measure and adjust the pH value of the buffer to 6.8.
6. ** Volumetric flask **: Select the appropriate specification volumetric flask according to the volume of the required buffer, such as 500 mL, 1000 mL, etc., to ensure the accuracy of the solution volume.
7. ** Glass rod **: Used to stir the solution to fully dissolve the solute.
8. ** Dropper **: When adjusting the pH value, accurately add glacial acetic acid dropwise.

Second, preparation steps
1. ** Calculate the amount of ammonium acetate **
According to the concentration and volume of the required buffer, calculate the quality of the required ammonium acetate through the formula. For example, to prepare 0.1 mol/L of ammonium acetate buffer 1000 mL, according to n = cV (n is the amount of substance, c is the concentration, V is the volume), the amount of ammonium acetate can be obtained n = 0.1 mol/L × 1 L = 0.1 mol. Ammonium acetate ($CH_3COONH_4 $) has a molar mass of about 77.08 g/mol, then the desired mass of ammonium acetate m = nM = 0.1 mol × 77.08 g/mol = 7.708 g.
2. ** Weigh ammonium acetate **
Use an electronic balance to accurately weigh the calculated mass of ammonium acetate and transfer it to a clean beaker. During the weighing process, attention should be paid to the calibration of the balance and operating specifications to ensure the accuracy of the weighing results.
3. ** Dissolve ammonium acetate **
Add an appropriate amount of distilled water to the beaker containing ammonium acetate and gently stir with a glass rod to promote the full dissolution of ammonium acetate. When stirring, the action should be slow to avoid the solution splashing out.
4. ** Transfer solution **
After the ammonium acetate is completely dissolved, carefully transfer the solution to the volumetric flask of the selected specification. During the transfer process, use a glass rod for drainage to ensure that the solution is fully transferred to the volumetric flask and no solution remains in the beaker.
5. ** Wash and bandwidth evaluation **
Wash beakers and glass rods 2-3 times with a small amount of distilled water, and transfer the washing liquid to a volumetric flask. Then continue to add distilled water to the volumetric flask until the liquid level is close to the scale line 1-2 cm. Use a dropper to add distilled water dropwise so that the concave liquid level of the solution is tangent to the scale line. During the bandwidth evaluation process, the line of sight should be kept level with the scale line to ensure the accuracy of the solution volume.
6. ** Preliminary adjustment of pH **
After shaking the solution in the volumetric flask well, transfer it to a clean beaker. Turn on the pH meter, and once it has stabilized, immerse the electrode in the solution to measure the current pH. Since the pH of the ammonium acetate solution itself is not 6.8, it needs to be adjusted with glacial acetic acid. While slowly adding glacial acetic acid, continuously stir the solution and closely observe the pH meter reading.
7. ** Precise pH adjustment **
When the pH is close to 6.8, add glacial acetic acid dropwise, stirring well after each addition and waiting for the pH meter reading to stabilize. Repeat this until the pH meter shows that the pH of the solution is precisely 6.8.
8. ** STORAGE **
Transfer the pH-adjusted ammonium acetate buffer to a clean, sealed reagent bottle and label it with information such as the buffer name, pH value, and preparation date. During storage, be careful to avoid contamination of the solution and temperature changes affecting its pH.