The major difference between a primary standard solution and the secondary standard solution is that primary solutions have higher purity and lower reactivity, whereas secondary solutions have a lower purity and higher reactivity.
Standardization of solutions is an analytical chemistry concept that is essential for the accuracy of titration. Standardization is a method of determining the exact concentration of the prepared solution by using the standard solution in the form of reference. Standard solutions have exactly defined concentrations, and we make them with standard substances.
It is required to all solutions should be standardized using a primary standard solution before they can be used in the titration process. This is because, even if you weigh the accurate quantity of the sample analyte needed to make a 0.1 molL-1 solution, the concentration may not be exactly it might be the presence of impurities or manual error.
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Table of Contents: What is the primary standard solution? |
However, because the primary standard solution's concentration is 99.9% accurate, hence, to determine the exact concentration of the prepared solution, you can titrate it against an appropriate primary reference solution. Primary standard solution and secondary standard solution are the two major types of standard solutions. Primary standards are used to standardize secondary standard solutions, while secondary standards are used for certain types of analytical experiments.
What is the primary standard solution?
The primary standard solution is a solution composed of primary standard substances. A primary standard is a high-purity substance (99.9%) that can be dissolved in a known volume of solvent to produce a primary standard solution. These substances are commonly used to determine the unknown concentration of a solution that is capable of reacting chemically with the primary standard.
Primary standards are highly pure and stable and have unique chemical and physical characteristics. Thus, we can prepare pure solutions with these chemicals. Primary standards are commonly employed in titrations and other analytical techniques to determine an unknown concentration of solutes.
Primary standard solution example:
Examples of primary standards for the titration of solutions, based on their high purity, are:
- Standardization of sodium thiosulfate (Na2S2O3) solution with potassium bromate (KBrO3).
- Sodium carbonate for the standardization of aqueous acids such as sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) solutions.
- Zinc powder (Zn) is used to standardize EDTA solutions.
- Sodium chloride (NaCl) is used as a primary standard for silver nitrate (AgNO3) reactions.
- Sodium carbonate (Na2CO3), potassium dichromate (K2Cr2O7), and potassium hydrogen phthalate (KHP) are some examples of primary standards.
What is a secondary standard solution?
A secondary standard solution is a chemical term for a solution that is titrated with a primary standard solution to determine its concentration. The secondary standard solution is composed of secondary standard substances for the specific analytical experiment. We should use primary standards to determine the concentration of these solutions. These types of standard solutions can be used to calibrate analytical instruments.
However, compared to primary standards, the purity of secondary standard solution is low, and the reactivity is high. Therefore, these solutions are easily contaminated due to their strong reactivity. Anhydrous potassium permanganate and sodium hydroxide are two common hygroscopic examples. Sodium hydroxide (NaOH) is a common example of secondary standard.
Difference between primary and secondary standard solutions:
- Primary standard solutions are made from primary standard substances, while secondary standard solutions are solutions prepared specifically for certain analysis.
- Primary standard solutions are highly pure (about 99.9%), while secondary standard solutions are not.
- Primary standards are less reactive or non-reactive, while secondary standards are more reactive compared to the primary standard.
- Primary standard solutions are rarely contaminated due to their low reactivity, while secondary standard solutions are quickly contaminated due to their high reactivity.
- Primary standards are non-hygroscopic, while secondary standards are slightly hygroscopic.
- Primary standard solutions are applied to standardize secondary standards and other reagents, while secondary standard solutions are applied for particular analytical studies.
- Primary standards are unaffected by atmospheric oxygen, while secondary standards are influenced by the atmosphere or /environment.
- Primary standards have known formulas and molecular weights, while the concentration of secondary standards varies over time.
Frequently Asked Questions (FAQ):
What is a primary standard?
A primary standard is an extremely pure reagent, has a high molecular weight, indicates the number of moles in a substance, can be easily weighed, and is used to cause a chemical reaction with another compound. Reagents are often used to determine whether a solution contains a specific chemical i.e. sodium carbonate (Na2CO3), potassium hydrogen phthalate (KHP), and potassium dichromate (K2Cr2O7), etc.
What is a secondary standard?
A secondary standard is a substance whose active agent content has been determined using a primary standard as a comparison. A secondary standard is made in the lab for a specific analysis and is generally standardized against a primary standard. NaOH, HCL, H2SO4, KOH, and KMnO4, etc. are some of the examples of secondary standards.
References:
- A.I. Vogel, Text Book of Quantitative Inorganic Analysis
- Helmenstine, Ph.D. Anne Marie. “Learn About Primary and Secondary Standards in Chemistry.”
- Wikipedia contributors. "Standard solution." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 16 Sep. 2021.
- Madhusha, November 07, 2017 Difference Between Primary and Secondary Standard Solution: Definition, Properties, Examples, https://pediaa.com/difference-between-primary-and-secondary-standard-solution/
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