This article describes in detail the preparation methods of common standard solutions in chemical laboratories, including pH standard solutions, elemental and common ion standard solutions, drying conditions of reference reagents, and their application in titration analysis. The preparation of pH standard solutions involves the use of primary and secondary reference reagents, emphasizing accurate preparation and calibration methods. The formulation of elemental and ionic standard solutions requires the selection and accurate weighing of high-purity reagents. The preparation and calibration of standard solutions in titration analysis include direct method and calibration method, and the precautions in the preparation and use process are put forward to ensure the accuracy of titration results.
Section 1: Preparation of commonly used solutions
General properties of commonly used acids and bases
Definition and classification of acids and bases
Acids refer to substances that can release hydrogen ions in water, which are divided into strong acids and weak acids; Alkali refers to substances that can release hydroxide ions, and is divided into strong bases and weak bases.
The basic characteristic of acid-base reactions – the reaction of acids with bases to form salts and water is called neutralization reaction, and this process is usually exothermic.
Preparation of commonly used acid solutions
The concentrated acid is gradually added to the water and stirred well to avoid the violent reaction caused by the direct addition of the concentrated acid to the water. Dilution is usually used to adjust to the desired concentration.
Preparation of commonly used alkaline solutions
Add a solid alkali or concentrated alkali solution to the water in proportion and stir until completely dissolved to ensure that the final solution concentration meets the requirements.
Preparation of commonly used saline solutions
The desired salt is dissolved in water, and the desired concentration of salt solution is obtained by adjusting the amount of salt and the stirring time.
Preparation of saturated solutions of commonly used reagents
A saturated solution is one in which the concentration of solutes in a solvent reaches a maximum value at a specific temperature. A saturated solution is prepared by adding excess solute and stirring until it no longer dissolves.
Preparation of special reagent solutions
According to the nature and use requirements of special reagents, specific preparation steps and concentration requirements are used to ensure the effectiveness and stability of the solution.
Preparation of indicator solutions
Acid-base indicator – Depending on the nature of the indicator, it is formulated using a standard acid or alkali solution to achieve the desired color change.
Redox Indicators – Monitor the progress of redox reactions by formulating the appropriate concentration of redox indicators.
Metal Ion Indicator – Formulate a suitable indicator solution to detect the presence of metal ions according to the needs of specific metal ions.
Adsorption Indicator - Formulation of adsorption indicator solution to measure adsorption phenomena and ensure the accuracy of their formulation.
Preparation of buffer solutions
Preparation of common buffer solutions – using a mixture of weak acids and their salts or weak bases and their salts, the pH value is adjusted to the desired range.
Brettan-Robbison buffer solution – Buffer solutions are prepared according to specific formulations and ratios to maintain a stable pH.
Clark-Lubbs buffer solution – used to maintain the pH stability of buffer solutions under specific experimental conditions.
Acetate-Sodium Acetate Buffer Solution – The combination of acetic acid and sodium acetate is used to regulate and stabilize the acidic environment of the solution.
Ammonia-Ammonium Chloride Buffer Solution - A suitable alkaline buffer solution is prepared by combining ammonia and ammonium chloride.
Section 2 Standard solutions commonly used in chemical laboratories and their preparations
Preparation of pH standard solutions
Primary and secondary pH reference reagents
Primary pH reference reagents provide higher purity and accuracy for calibration of high-precision instruments. Secondary pH reference reagents are suitable for general laboratory needs, but they are slightly less precise and stable. Commonly used pH standard solutions include those with pH 4.00, pH 7.00, and pH 10.00.
Preparation method – using a predetermined concentration of acid or alkali solution, adjust the pH by adding a buffer of known concentration. Make sure to use high-purity reagents and deionized water to get an accurate pH. Calibrate with a pH meter to ensure that the pH of the solution is accurate.
Preparation of standard solutions of elements and common ions
Preparation method – First, select high-purity reagents, weigh them accurately, and dissolve them in deionized water. For elemental standard solutions, such as sodium, potassium, calcium, etc., the corresponding salts (e.g., sodium chloride, potassium chloride, calcium chloride) are used to precisely prepare the required concentration. For common ions, such as chloride and sulfate, standard solutions are prepared using the corresponding salt or acid solutions.
Reference reagents and drying conditions in titration assays
Primary and secondary reference materials
Primary reference materials have the highest purity and accuracy and are commonly used to calibrate titrations and standard solutions. Secondary reference materials are slightly less pure, but sufficient for general titration needs. Reference reagents should be dried under specific conditions, such as oven drying or stored in a desiccator to ensure their quality and stability.
Preparation and calibration of standard solutions in titration analysis
Direct method – by directly preparing the solution to the desired concentration and performing the necessary calibration. Commonly used in basic titration analysis.
Calibration – Calibration is performed with a standard solution of known concentration to ensure the accuracy of the solution to be measured. Commonly used methods include acid-base titration, redox titration, etc.
Preparation and use precautions: When preparing standard solutions, use a precision balance to weigh the reagents and ensure the purity of the reagents. The dissolution and stirring during the preparation process should be sufficient to ensure that the solution is homogeneous. When used, regular calibration and calibration are required to ensure the accuracy of the titration results.
summary
This paper systematically describes the preparation and use of standard solutions in chemistry laboratories. First, pH standard solutions need to be prepared using precise primary and secondary reference reagents and calibrated with a pH meter. Secondly, the preparation of elemental and ionic standard solutions requires the selection of high-purity reagents and accurate weighing. Reference reagents need to be properly dried in titration assays and their quality is ensured by the use of primary or secondary reference materials. In the preparation and calibration of standard solutions, the direct method and the calibration method have their own applications, and it is necessary to pay attention to precise operation and regular calibration to ensure the accuracy of experimental results.
