Preparation of Ammonium Acetate Buffer (pH5)
1. Required Materials
1. ** Ammonium Acetate **: Analytical purity level to ensure that its purity is sufficient to avoid the introduction of impurities affecting the pH value and other properties of the buffer.
2. ** Glacial Acetic Acid **: Also analytically pure, used to adjust the pH value of the buffer.
3. ** Distilled Water **: Use freshly prepared distilled water or deionized water to ensure its purity without impurity interference.
4. ** Instrument **: electronic balance (accurate to 0.001g) for accurate weighing of ammonium acetate; acid burette for accurate measurement of glacial acetic acid; volumetric flask (e.g. 1000mL) for bandwidth evaluation of buffer formulation; pH meter for measuring and calibrating the pH of buffer; glass rod for stirring the solution to mix it evenly.

Second, preparation steps
1. ** Calculation **: According to the buffer solution pH calculation formula $pH = pKa +\ lg\ frac {[A ^ -]} {[HA]} $ (for acetic acid-ammonium acetate buffer system, acetic acid $pKa = 4.75 $), to prepare pH = 5 buffer, set the ammonium acetate concentration of $c_1 $, acetic acid concentration of $c_2 $, then 5 dollars = 4.75 +\ lg\ frac {c_1} {c_2} $, you can get $\ lg\ frac {c_1} {c_2} = 0.25 $, that is, $\ frac {c_1} {c_2}\ approx 1.78 $. Usually a suitable total concentration can be determined first. Assuming a total concentration of $0.1mol/L $, the ammonium acetate concentration is about $0.064mol/L $, and the acetic acid concentration is about $0.036mol/L $.
2. ** Weigh ammonium acetate **: Use an electronic balance to accurately weigh a certain mass of ammonium acetate. If 1L of the above buffer is prepared, the molar mass of ammonium acetate is $77.08g/mol $, then the required mass of ammonium acetate is $m = 0.064mol/L × 1L × 77.08g/mol\ approx 4.933g $. Pour the weighed ammonium acetate into a clean beaker.
3. ** Dissolve ammonium acetate **: Add an appropriate amount of distilled water to a beaker containing ammonium acetate and stir with a glass rod to dissolve it completely. Note that the volume of distilled water added should not be too much, about one-third to one-half of the total volume, for subsequent bandwidth evaluation operations.
4. ** Measure glacial acetic acid **: Accurately measure a certain volume of glacial acetic acid with an acid burette. The density of acetic acid is about $1.05g/mL $, and the concentration of the substance is about $17.4mol/L $. To obtain $0.036mol/L $of acetic acid, the required glacial acetic acid volume in 1L solution is $V =\ frac {0.036mol/L × 1L} {17.4mol/L} × 1000mL\ approx 2.07mL $. Slowly add the measured glacial acetic acid to the solution of dissolved ammonium acetate, while stirring well.
5. ** bandwidth evaluation **: Transfer the above mixed solution to a 1000mL volumetric flask, rinse the beaker and glass rod with a small amount of distilled water 2-3 times, and pour the rinsing liquid into the volumetric flask. Then add distilled water to the volumetric flask to the scale line. Pay attention to observation during bandwidth evaluation. When the liquid level is close to the scale line 1-2cm, use a rubber head dropper to add distilled water dropwise until the concave liquid level of the solution is tangent to the scale line.
6. ** Calibration of pH value **: Pour the prepared solution into a clean beaker and measure its pH value with a pH meter. Due to the possible errors in the calculation and operation process, if the measured pH value is slightly deviated from 5, it can be fine-tuned by adding a small amount of glacial acetic acid or ammonium acetate solution dropwise until the pH value reaches 5 accurately.

III. Precautions
1. ** Reagent purity **: Ensure the purity of ammonium acetate and glacial acetic acid. Impurities may affect the performance and pH stability of the buffer solution.
2. ** Instrument calibration **: Instruments such as electronic balances and pH meters need to be calibrated before use to ensure the accuracy of measurement and preparation.
3. ** Operation Specifications **: During the operation of measuring and transferring the solution, it is necessary to strictly follow the operation specifications of the chemical experiment to avoid the loss of the solution or the introduction of impurities.
4. ** Storage Conditions **: The prepared ammonium acetate buffer (pH 5) should be stored in a clean and sealed container to avoid long-term contact with the air to prevent gases such as carbon dioxide from affecting the pH value. At the same time, it should be stored at a suitable temperature to avoid excessive temperature changes affecting the properties of the buffer.