Question

Kilogram Standard Although the standard kilogram is stored at constant temperature and humidity, unwanted matter can build up on its surface. Scientists have been looking for a more reliable standard for mass. Research and describe alternative standards that have been proposed. Find out why no alternative standard has been chosen.

Short answer

The quest for a more reliable standard kilogram has led to several proposed alternatives, such as the Avogadro Project, Watt Balance, and Ion Accumulation. These methods seek to define the kilogram in terms of fundamental constants, like the Avogadro constant and Planck's constant, or precise ion counting. However, none of these alternatives have been chosen yet due to challenges in ensuring accuracy, universality, practicality, and the complexities of the required instruments and procedures. The search for a suitable replacement for the current standard kilogram continues as scientists work to address these challenges.

Step-by-step solution

Introduction to the Problem

The standard kilogram, used as a reference for mass measurement, is a physical object stored in carefully controlled conditions. However, it can still accumulate unwanted matter, affecting its mass. Thus, scientists have been searching for more reliable alternative standards. In this exercise, we will discuss some proposed alternatives and the reasons why they have not been chosen yet.

Alternative 1: Avogadro Project

The Avogadro Project seeks to define the kilogram in terms of the Avogadro constant, which is the number of atoms in a fixed amount of a substance. In this approach, a sphere of a specific isotope of silicon is purified, and its mass is determined by counting the atoms in the sphere. The number of atoms is then related to the Avogadro constant, providing a precise definition of the kilogram. However, this alternative has not been chosen because it is challenging to count atoms in a sphere accurately. Additionally, the process of making a perfect silicon sphere with the desired isotope purity is also complicated and expensive.

Alternative 2: Watt Balance

The Watt Balance method aims to redefine the kilogram by directly relating it to the Planck's constant, a fundamental constant in physics. The process involves an instrument that compares the mechanical power needed to balance the weight of an object with the electrical power required to generate an equivalent electromagnetic force. Despite its potential advantages, the Watt Balance method has not been chosen yet, mainly due to the complexity of the instrument and the need for additional research to ensure the accuracy and universality of the measurements.

Alternative 3: Ion Accumulation

The ion accumulation method involves counting a precise number of ions and accumulating them until reaching the desired mass. In this approach, the kilogram would be defined based on the mass of a fixed number of ions of a specific element. This method has not been chosen because it requires an extremely accurate ion trap device and sophisticated techniques to count ions and accumulate them. Moreover, the time required to accumulate a significant mass of ions is quite long, making the process impractical.

Conclusion

The search for a more reliable standard for mass is ongoing, with several alternative methods proposed, such as the Avogadro Project, Watt Balance, and Ion Accumulation. However, none of these alternatives have been chosen for various reasons, primarily due to the challenges in ensuring accuracy, universality, and practicality. Scientists will continue to investigate these methods and others to find a suitable replacement for the current standard kilogram.

Key concepts

Mass Measurement

Mass measurement is a fundamental aspect of science, crucial for both theoretical and practical applications. Traditionally, the standard kilogram has been used as the reference for mass measurements. This is a physical artifact that needs to be kept in specific environmental conditions. Unfortunately, even under controlled conditions, it can gather unwanted material, causing variations in mass. These variations necessitate finding a more stable and reliable standard. Researchers have thus explored different techniques to establish a new definition of mass, focusing on fixed constants of nature or intrinsic properties of matter itself.

While the current kilogram standard involves hands-on approaches, alternate measurement methods aim to use constants that remain unvarying over time. This innovation is crucial to improving the precision and reliability of measurements worldwide, facilitating advancements in scientific research.

Avogadro Project

The Avogadro Project is a fascinating initiative aiming to redefine the kilogram by using the Avogadro constant. This constant represents the number of atoms in one mole of a substance, and it serves as a bridge between macroscopic and atomic scales. The project focuses on creating a sphere made from a specific isotope of silicon, due to its well-known atomic structure, which makes calculations easier.

One of the critical steps is counting the precise number of atoms within the silicon sphere, linking the mass directly to the Avogadro constant. By establishing this direct relationship, scientists can define the kilogram without relying on a physical artifact. However, challenges arise in purifying the silicon isotope and in accurately counting the atoms within a solid sphere. These hurdles have prevented this method from becoming the standard, but it marks a substantial step forward in the journey for a new definition.

Watt Balance

The Watt Balance technique offers another promising path to redefine the kilogram. In this method, the mass is linked to Planck's constant, a well-defined constant in physics. The Watt Balance operates by measuring the electrical power required to counterbalance a known weight's mechanical force through electromagnetic means.

A major benefit of the Watt Balance is its potential to provide a measurement based on constants of physics, ensuring universality. However, constructing and operating a Watt Balance is complex and requires continued research to confirm its accuracy at a global scale. Nevertheless, it offers an exciting alternative, emphasizing the convergence of electrical and mechanical systems to establish a mass standard that might replace the tangible kilogram.

Ion Accumulation

Ion accumulation represents a unique method focused on defining mass through the collection of ions. This approach involves gathering a specific number of ions until their cumulative mass reaches that of a kilogram. The key is defining the mass in terms of a fixed number of ions of a particular element, providing a consistent standard.

This process typically requires a highly accurate ion trap to count and accumulate ions, which is technically sophisticated. Moreover, the time needed to collect a kilogram's worth of ions is considerable, making the technique less practical. Despite the precision that ion accumulation potentially offers, these challenges have prevented it from being adopted as the official mass standard. Nonetheless, ion accumulation continues to be a subject of interest for its innovative approach to mass definition.