STANDARD SOLUTIONS AND DILUTION FACTOR

Introduction

A standard solution is a solution whose concentration is accurately known. It is used as a reference or comparison against other solutions in chemical analysis or experiments. A standard solution is usually prepared by dissolving a precise amount of a pure substance, known as the primary standard, in a solvent, typically water.

The concentration of a standard solution is determined by carefully measuring the mass of the primary standard and the volume of solvent used to prepare the solution. Once the concentration is determined, the standard solution can be used to accurately determine the concentration of other solutions through a process called titration.

Standard solutions are important in analytical chemistry because they provide a precise and reproducible reference point against which other solutions can be measured. They are commonly used in titrations to determine the concentration of acids, bases, and other substances in a sample.

 

The preparation of some primary standards are as follows:

1) Anhydrous Na2CO3

• Weigh 10 grams of sodium carbonate (Na2CO3) and dissolve it in distilled water in a 1-liter volumetric flask.
• Dilute the solution to the mark with distilled water and mix it thoroughly.
• This solution is now a 0.1 N (normal) solution of Na2CO3, which can be used as a primary standard.

 

2) (COOH)2, 2H2O

• Weigh accurately about 2 grams of oxalic acid dihydrate [(COOH)2, 2H2O] and dissolve it in distilled water in a 250 ml volumetric flask.
• Dilute the solution to the mark with distilled water and mix it thoroughly.
• This solution is now a 0.1 N (normal) solution of oxalic acid, which can be used as a primary standard.

 

3) H2C2O4.2H2O

• Weigh accurately about 1 gram of oxalic acid dihydrate (H2C2O4.2H2O) and dissolve it in distilled water in a 250 ml volumetric flask.
• Dilute the solution to the mark with distilled water and mix it thoroughly.
• This solution is now a 0.1 N (normal) solution of oxalic acid, which can be used as a primary standard.

 

Note: It is important to use analytical grade chemicals, glassware, and distilled water for the preparation of primary standards to obtain accurate and reliable results.

 

1. Primary Standard: A primary standard is a highly pure substance that is used as a reference material for the calibration of analytical instruments or for the preparation of standard solutions. Primary standards are usually characterized by their high purity, stability, and reproducibility.
2. Secondary Standard: A secondary standard is a substance that is used as a reference material for the calibration of analytical instruments or for the preparation of standard solutions, but it is not as pure or stable as a primary standard. Secondary standards are typically less expensive and more readily available than primary standards, but they must be carefully characterized and tested to ensure their suitability for use in analytical procedures.
3. Standard Solution: A standard solution is a solution of a known concentration that is used as a reference material in analytical procedures. Standard solutions can be prepared from primary or secondary standards, and they are typically used for calibration, quality control, and method validation purposes in analytical chemistry. The concentration of a standard solution is usually expressed in units of moles per liter (M), millimoles per liter (mM), or micromoles per liter (μM), depending on the analytical technique being used.

 

Preparation of solutions from liquid solutes by the method of dilution

The method of dilution is commonly used to prepare solutions from liquid solutes. In this method, a small amount of solute is dissolved in a small amount of solvent to make a concentrated solution, and then more solvent is added to dilute the solution to a desired concentration.

The following are the steps to prepare a solution by the method of dilution:

1. Determine the desired concentration of the solution. This will determine the amount of solute and solvent needed.
2. Measure out the appropriate amount of solute (in mL or g) using a graduated cylinder or balance.
3. Add the solute to a volumetric flask or beaker containing a small amount of solvent.
4. Stir the mixture until the solute dissolves completely.
5. Add more solvent to the flask or beaker, up to the desired volume, and stir the mixture again.
6. Record the final volume and concentration of the solution.

Note: It is important to accurately measure the volume of the solvent and the solute to ensure that the final concentration is accurate. Also, be sure to stir the solution thoroughly to ensure that the solute is evenly distributed throughout the solution.

 

Dilution is the process of reducing the concentration of a solution by adding more solvent to it. The dilution factor is the ratio of the final volume of the solution to the initial volume of the concentrated solution. It is also known as the dilution ratio.

The dilution factor is calculated by dividing the final volume of the solution by the initial volume of the concentrated solution. For example, if you add 10 mL of a concentrated solution to 90 mL of solvent to make a total volume of 100 mL, the dilution factor is 100/10 = 10.

The dilution factor can also be expressed as a fraction or a percentage. In the example above, the dilution factor can be expressed as 1/10 or 10%. This means that the concentration of the diluted solution is 10% of the concentration of the original solution.

Dilution is an important concept in chemistry and is used in many applications, including preparing solutions for experiments, analyzing samples, and in industrial processes. Dilution is often necessary to obtain a solution with the desired concentration for a specific application.