Standard Solutions, saturated and supersaturated solutions

Description, classification, preparation, and applications of standard solution, stock standard solutions, working standard solutions, primary standard solutions, secondary standard solutions, saturated solutions, and super saturated solutions.
We explore the possibilities of understanding above state topics in a simplistic manner to build a base among the first year students of B.Sc. allied health sciences

1. Standard, saturated and supersaturated solutions Karthik G Kamath K Associate Professor Department of Biochemistry

2. Standard Solution Solution containing an accurately known concentration Dissolving a known mass into a solvent of precise volume Or diluting solution of known concentration with more solvent Used for determination of solutions with unknown concentration – titration

3. Uses of standard solution Titration Determination of concentration using a calibration curve

4. Types of standard solutions Analytical standards can be categorised into Primary standards – compounds of known stoichiometry, high purity, & high stability Prepared using accurately weighing a known quantity of solute followed by dilution to a precise volume

5. Types of standard solutions Secondary standards – compounds with concentration determined by a primary standard They do not satisfy the requirements of primary standards

6. Types of standard solutions Based on use and storage standard solutions can be of Stock standard solutions – concentrated versions of standard solutions Can be used on its own Or part of a mixture of complex solutions

7. Types of standard solutions Preparation of stock standard Calculation – calculate the mass to be weighed for the required strength of the solution Weigh – accurately the amount of solute required Dissolve – the solute in precise volume of the solvent

8. Types of standard solutions Adjust the pH – if required Adjust the vol – to the required, after the pH is set Label and store

9. Types of standard solutions Working standard solutions Prepared from stock solution By diluting small volume of stock using the diluent

10. Types of standard solutions Preparation of working standard Calculation – calculate the volume of the stock standard for the required strength of the working standard solution Dilute – the stock solution in precise volume of the diluent Adjust the pH – if required Adjust the vol – to the required, after the pH is set Label and store

11. Saturated solution Is a solution that contains the maximum amount of solute that can be dissolved under the condition at which the solution exists Undissolved solute lies at the bottom A saturated solution is a solution that is in equilibrium with respect to a given dissolved substance

12. Preparation It is prepared by continuously adding solute to the solution until a stage is reached where the solute appears as a solid precipitate or as crystals to form a highly saturated solution. Consider the process of adding table sugar to a container of water. Initially, the added sugar dissolves as the solution is stirred.

13. Finally, as more sugar has added a point is reached where no amount of stirring will cause the added sugar to dissolve. The last added sugar remains as a solid on the bottom of the container, the solution is saturated

14. Supersaturated solution A solution contains more dissolved substance than a saturated solution does A supersaturated solution is a solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature

15. Preparation Special conditions need to be met in order to generate a supersaturated solution. The more heat is added to a system, the more soluble a substance becomes. Therefore, at high temperatures, more solute can be dissolved than at lower temperatures. If this solution were to be suddenly cooled at a rate faster than the rate of precipitation, the solution will become supersaturated until the solute precipitates to the temperature-determined saturation point.

16. The precipitation or crystallization of the solute takes longer than the actual cooling time because the molecules need to meet up and form the precipitate without being knocked apart by the solvent. Thus, the larger the molecule, the longer the solute will take to crystallize due to the principles of Brownian motion.