Final answer:
A primary standard is a highly pure, stable, non-hygroscopic substance with a high molecular weight used for calibrations in analytical chemistry. Its requirements include high purity, stability, non-hygroscopic nature, and a high molecular weight for accurate measurements in titrations.
Step-by-step explanation:
A primary standard in chemistry is a substance that is extremely pure, stable, non-hygroscopic, and has a high molecular weight. This substance is used to calibrate instruments and for preparing solutions used in titrations in analytical chemistry. The requirements for a primary standard include high purity, to ensure that its weight reflects only the substance of interest; stability, so it does not change over time; it must be non-hygroscopic, meaning it does not absorb water from the air, which can alter its weight; and it must have a predictable reaction in chemical processes.
Requirements for a primary standard include:
- High purity, to ensure the standard's mass is accurate and consistent.
- Stability over time, to maintain its purity and reactivity.
- Non-hygroscopic nature, meaning it does not absorb moisture from the air.
- Large molar mass, providing accurate measurements in titration.
- Solubility, to enable dissolution in solutions for titrations.
Understanding primary standards is essential in fields like environmental science, where such standards are applied in determining the safety of drinking water. For instance, the National Primary Standards for Drinking Water are based on human health and include limits on toxic substances such as mercury (Hg), arsenic (As), and uranium (U), to ensure the protection of public health.