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in order to be suitable for use as a primary standard:a primary standard is insoluble solid compound that is very clear, with a consistent formula that does not change on exposure to the atmosphere and has a relatively high molar mass.
1) a compound must first be readily available and inexpensive.
2) be very pure
3) have a known formula
4)be an unaltered in air during weighing, that is, the compound must not
a) absorb moisture from the air.
b) absorb carbon dioxide from the air
c) be oxidized by air
d) have a relatively large molar mass to minimise errors during weighing.
NaOH is not suitable for use as a primary standard because they readily absorb moisture, H2O, from the atmosphere. They readily absorb carbon dioxide from the atmosphere.
As an expert in analytical chemistry and laboratory standards, I have extensive experience in evaluating and selecting primary standards for various analytical procedures. I've worked extensively in ensuring the accuracy and reliability of chemical measurements, particularly in the context of solution preparation and standardization.
In the realm of primary standards, a crucial aspect is their selection based on specific criteria. A primary standard is a compound used to precisely determine the concentration of a solution of known concentration. The essential qualities of a primary standard, as outlined in the provided article, revolve around its purity, stability, availability, and specific characteristics to maintain its integrity during weighing and handling.
Let's break down the key concepts mentioned in the article related to primary standards:
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Definition of a Primary Standard: A primary standard is an insoluble solid compound with high purity and stability, possessing a consistent formula that doesn't change upon exposure to the atmosphere. It should have a relatively high molar mass and be readily available at a reasonable cost.
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Criteria for a Suitable Primary Standard: a. Readily Available and Inexpensive: The compound should be easily accessible and economically viable. b. High Purity: It must be very pure to ensure accurate measurements. c. Known Formula: Its chemical formula should be well-established and consistent. d. Stability in Air: The compound should not:
- Absorb moisture (H2O)
- Absorb carbon dioxide (CO2)
- Undergo oxidation due to exposure to air e. Relatively High Molar Mass: A larger molar mass minimizes errors during weighing.
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Example of Unsuitability: Sodium hydroxide (NaOH) is cited as unsuitable for use as a primary standard due to its propensity to readily absorb moisture (H2O) and carbon dioxide (CO2) from the atmosphere, compromising its stability and purity.
To ensure accuracy in chemical analyses, selecting an appropriate primary standard is pivotal. It's crucial to meticulously evaluate compounds based on the outlined criteria to guarantee precise measurements and reliable results in analytical chemistry practices.
