A good primary standard meets the following criteria:
- Has a high level of purity
- Has low reactivity (high stability)
- Has a high equivalent weight (to reduce error from mass measurements)
- Is not likely to absorb moisture from the air ( hygroscopic ), to reduce changes in mass in humid versus dry environments
- Is nontoxic
- Is inexpensive and readily available
What are the criteria of a primary standard?
A primary standard material should be extremely pure which means that it should be a chemical of high grade of purity, preferably 99.98%. In a chemistry lab you will come across chemicals of different grade of purity. If you check the label you will notice a number with percentage termed as purity.
What are the criteria of primary standard and secondary standard?
Primary standards are reagents that can involve in chemical reactions. These compounds are often used to determine the unknown concentration of a solution that can undergo a chemical reaction with the primary standard. A secondary standard solution is a solution that is made specifically for a certain analysis.
How do you prepare primary and secondary standard solution?
To prepare the secondary standard solution, an aqueous solution of high purity must be used. Water must be deionized when used as an aqueous solvent. Standard solutions prepared without pure solvent are worthless (These points apply to primary standard solutions as well).
What are the criteria of a secondary standard?
A secondary standard is a substance whose active agent contents have been found by comparison against a primary standard. This means it is usually standardized against a primary standard. Secondary standard solutions are used to calibrate analytical equipment and analytical techniques.
What are the major characteristics of a primary standard and what is the importance of using a primary standard?
A primary standard is a highly pure and stable chemical reagent used to prepare standard solutions, usually for titration and making secondary standards and dilutions. In chemistry, a primary standard is a reagent that is very pure, stable, not hygroscopic, and has a high molecular weight.
What are primary secondary and working standards?
Secondary standards are calibrated with reference to a primary standard. The third level of standard, a standard which is periodically calibrated against a secondary standard, is known as a working standard. Working standards are used for the calibration of commercial and industrial measurement equipment.
What are two primary standards examples?
The primary standard is a reagent with high purity, high molar mass, and hygroscopic characteristics. Examples of primary standards are: Sodium carbonate (Na2CO3 ) Sodium tetraborate (Na2 B407)
What is titration in chemistry?
Titration is a process in which small amounts of a reagent are added to a solution until a chemical reaction occurs. The reaction confirms that the solution is at a specific concentration. Primary standards are often used to make standard solutions, solutions with a precisely known concentration.
What is reagent in chemical?
A reagent is a chemical used to cause a chemical reaction with another substance. Often, reagents are used to test for the presence or quantity of specific chemicals in a solution.
What is a primary standard in chemistry?
Twitter Twitter. Anne Marie Helmenstine, Ph.D. Updated February 04, 2020. In chemistry, a primary standard is a reagent that is very pure, representative of the number of moles the substance contains, and easily weighed. A reagent is a chemical used to cause a chemical reaction with another substance. Often, reagents are used to test ...
What is secondary standard?
A related term is secondary standard, a chemical that has been standardized against a primary standard for use in a specific analysis. Secondary standards are commonly used to calibrate analytical methods. NaOH, once its concentration has been validated through the use of a primary standard, is often used as a secondary standard.
What is the best solution to standardize EDTA?
Zinc powder, which can be used to standardize EDTA (ethylenediaminetetraacetic acid) solutions after it has been dissolved in hydrochloric or sulfuric acid. Potassium hydrogen phthalate, or KHP, which can be used to standardize perchloric acid and an aqueous base in an acetic acid solution.
Does NaOH absorb carbon dioxide?
For example, sodium hydroxide (NaOH) tends to absorb moisture and carbon dioxide from the atmosphere, thus changing its concentration. A 1-gram sample of NaOH might not actually contain 1 gram of NaOH because additional water and carbon dioxide might have diluted the solution. To check the concentration of NaOH, a chemist must titrate a primary standard—in this case, a solution of potassium hydrogen phthalate (KHP). KHP does not absorb water or carbon dioxide, and it can provide visual confirmation that a 1-gram solution of NaOH really contains 1 gram.
Is reagent needed to determine concentration?
It might seem odd that a reagent is needed to establish the concentration of a chemical in solution. In theory, it should be possible to simply divide the mass of the chemical by the volume of the solution. But in practice, this isn't always possible. For example, sodium hydroxide (NaOH) tends to absorb moisture and carbon dioxide from ...
Why is HCl not a primary standard?
HCl is not a primary standard because it is in a gaseous state at room temperature. If it dissolved in water (~37%), still not a primary standard, due to the continuous evaporation at room temperature. A good primary standard is nonreactive toward the atmosphere.
Why are primary standards used?
Primary standards are used for the standardization of solutions because they have high purity, are cheap, hygroscopic, and nontoxic. Generally, they are used in titrations like,
Why is sodium carbonate used to standardize HCl?
Sodium carbonate is used to standardize HCl because Na 2 CO 3 is a primary standard with a relatively high molecular weight and is highly stable. Moreover, it is a base so it can be titrated against a specific volume of HCl.
What is the standard for HPLC?
The standard used for the standardization of HPLC (High pressure liquid chromatography) is caffeine. 1,3,7-trimethylxanthine (caffeine) a central nervous stimulant is used in standardization processes due to its high purity and stability. Its solution in water is usually applied as a standard for HPLC and is run just like a sample. High R 2 values indicate the correct working of HPLC.
What is the molecular weight of sodium chloride?
Sodium chloride is used as the primary standard for this purpose. It has a relative molecular weight of 58.44 g/mol. To be exact, 1.4516 g of salt is weighed to form 0.1000 M solution in 250 ml of solution. Salt is added to the volumetric flask and dissolved in a few ml then diluted up to the 250 ml mark. This solution is employed for the standardization of silver nitrate solution.
What is the purpose of calculating the weight of a standard chemical?
Calculations are done to find the approximate weight of the primary standard chemical needed to make up the known volume of the standard solution.
What is secondary standard solution?
The secondary standard solution is a solution, in which the concentration of dissolved solute has not been determined, from the weight of the compound but by the titration against a primary standard.
Primary Standard
Secondary Standard
How to Make Standard Solutions
Primary Standards in The Wet Analysis
Calibration of Instruments by Primary Standards
Concepts Berg