Difference Between Primary and Secondary Standard Solution

The key difference between primary and secondary standard solution is that primary standard solution has a high purity and less reactivity whereas secondary solution has a less purity and high reactivity.

Standardization is the process of finding the exact concentration of a prepared solution using a standard solution as the reference. Standard solutions have accurately known concentrations and we prepare these solutions using standard substances. The two major standard solution forms are primary standards and secondary standards. We use primary standards for the standardization of secondary standard solutions. Secondary standards are useful for specific analytical experiments.

1. Overview and Key Difference
2. What is Primary Standard Solution
3. What is Secondary Standard Solution
4. Side by Side Comparison – Primary vs Secondary Standard Solution in Tabular Form
5. Summary

What is Primary Standard Solution?

Primary standard solutions the solutions made form primary standard substances. These substances have a high purity which nearly equals 99.9% purity. We can dissolve this substance in a known volume of solvent in order to obtain the primary standard solution. These solutions can involve chemical reactions. Therefore, we can use this reagent to determine the unknown concentration of a solution that undergoes a particular chemical reaction.

These solutions have specific chemical and physical properties. For example, these solutions have a high purity and are highly stable. In titrations, we should standardize all the solutions we use for the titration before doing the experiment. This is because, even though we take the exact amounts of substances to make those solutions, they may not have the exact concentration that we expect because those substances are not that much pure. Some examples of primary standards include potassium bromate (KBrO3), sodium chloride, zinc powder, etc.

What is Secondary Standard Solution?

Secondary standards solutions are the solutions made from secondary standard substances. We prepare these solutions for a specific analytical experiment. We should determine the concentration of these solutions using primary standards. Most of the times, these solutions are useful for the calibration of analytical instruments.

Difference Between Primary and Secondary Standard Solution

Figure 01: Potassium Permanganate

However, the purity of these solutions is less compared to primary standards and the reactivity is high. Due to this high reactivity, these solutions get contaminated easily. Some common examples are anhydrous sodium hydroxide and potassium permanganate. These compounds are hygroscopic.

What is the Difference Between Primary and Secondary Standard Solution?

Primary standard solution is the solution made form primary standard substances. It has a high purity and a low reactivity. Secondary standards solutions are the solutions made from secondary standard substances. These are less pure and highly reactive. This is the main difference between primary and secondary standard solution. Furthermore, due to their low reactivity, primary standard solutions rarely get contaminated whereas as secondary standards solutions are highly reactive, they easily get contaminated. Therefore, we should standardize secondary standards solutions before use.

Summary – Primary and Secondary Standard Solution

Standard solutions are important in determining the unknown concentrations of experimental solutions. There are two forms as primary standards and secondary standards. The difference between primary and secondary standard solutions is that primary standard solutions have a high purity and less reactivity whereas secondary solutions have a less purity and high reactivity.

Reference:

1. Helmenstine, Anne Marie, Ph.D. “What Is a Primary Standard in Chemistry?” ThoughtCo, Apr. 18, 2018. Available here
2. International Union. “Standard Solution.” IUPAC Gold Book – Capillary Condensation. Available here