What Is An Analytical Balance | Its Duties?

November 3, 2021

Analytical balance

The balance is an instrument used to measure mass. Analytical balance is a kind of balance mainly used to measure small masses.

This type of balance is one of the most widely used measuring instruments in the laboratory and on which basically all analytical results depend.

Modern analytical balances, which can offer reading precision values ​​from 0.1 µg to 0.1 mg, are well developed so that the use of special rooms for weight measurement is not necessary. Even so, the simple use of electronic circuits does not eliminate the interactions of the system with the environment. Of these, the physical effects are the most important because they cannot be suppressed.

Temperature

Observed effect: the counter constantly varies in one direction.

Reason: The existence of a temperature difference between the sample and the measurement chamber environment causes drafts. These air currents generate forces on the measuring plate making the sample appear lighter (known as dynamic fluctuation). This effect only disappears when thermal equilibrium is established.

Furthermore, the film of moisture that covers any sample, which varies with temperature, is masked by dynamic fluctuation. This makes a colder object appear heavier, or a warmer object appear lighter.

Corrective actions:

  • Never weigh samples removed directly from stoves, flasks or refrigerators.
  • Always allow the sample to reach the same temperature as the laboratory or the measuring chamber.
  • Always try to handle measuring bottles or samples with tweezers. Not being possible, use a paper band.
  • Do not touch the measuring chamber with your hands.
  • Use measuring jars with the smallest area possible.

Mass variation

Observed effect: the counter indicates readings that increase or decrease, continuously and slowly.

Reason: increase in mass due to a hygroscopic sample (increase in atmospheric humidity) or loss of mass due to evaporation of water or volatile substances.

Corrective actions:

  • Use clean and dry bottles and always keep the measuring plate free of dust, contaminants or liquid drops.
  • Use measuring bottles with narrow necks.
  • Use lids or corks on measuring jars.

Electrostatics

Observed effect: The balance counter becomes unstable and indicates different masses for each measurement of the same sample. The reproducibility of the results is compromised.

Reason: The measuring bottle is electrostatically charged. These charges are formed by friction or during the transport of the materials, especially if they are in granules or powder. If the air is dry (relative humidity less than 40%) these electrostatic charges are retained or are slowly dispersed. Measurement errors occur due to electrostatic attractive forces that act between the sample and the environment. If the sample and the environment are under the same effect of electric charges of the same signal [+ or -] there is repulsion, while under the effect of opposite charges [+ and -] attractions are observed.

Corrective actions:

  • Increase atmospheric humidity by using a humidifier or by appropriate settings in the air conditioning system (ideal relative humidity: 45-60%).
  • Discharge electrostatic forces by placing the measuring bottle in a metal container before measuring the weight.
  • Connect the scale to an efficient “ground wire”.

Magnetism

Observed effect: low reproducibility. The result of the measurement of the weight of a metallic sample depends on its position on the balance plate.

Reason: If the material is magnetic (eg: iron, steel, nickel, etc.) mutual attraction may be occurring with the balance plate, and forces may be being created causing a false measurement.

Corrective actions:

  • If possible, demagnetize the magnetic iron samples.
  • As the magnetic forces decrease with distance, separate the sample from the dish using a non-magnetic holder (eg, an upside down Bécquer or an aluminum holder).
  • Use the upper hook of the balance plate, when there is one.

Gravitation

Observed effect: the weight value varies according to latitude. The closer to the equator, the greater the centrifugal force due to the rotation of the earth, which is opposed to the gravitational force. Thus, the force acting on a mass is greater at the poles than at the equator. The measurements also depend on the altitude in relation to sea level (more precisely, in relation to the center of the earth). The higher it is, the lower the gravitational pull, which decreases with the square of the distance.

Corrective actions:

  • Differential or comparative or precision measurements, made at different latitudes (eg, on the ground floor or on other floors of the same building) must be corrected.

Push

Observed effect: the result of a weight measurement made at atmospheric pressure is not the same as under vacuum.

Reason: this phenomenon is explained by Archimedes’ principle, according to which “a body suffers a weight loss equal to the weight of the mass of the environment that is dislodged by it.” When measuring the weight of very dense (ex: Hg) or not very dense (ex: water) materials, corrections should be made, in favor of precision.

Corrective actions:

  • Differential or comparative or highly precise measurements, carried out on different days, must always be corrected in relation to thrust, taking into account temperature, pressure and atmospheric humidity. Ordinary laboratory work usually dispenses with these actions.
Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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