# Using a Balance to Measure Mass

A kid’s natural curiosity will fuel a desire to learn about all the things that surround them. Introducing kids to concepts like mass early can help them effortlessly grasp more complicated concepts in physics later on.

Mass is a quantitative measure of the inertia of matter. It doesn’t depend on the shape of atoms in the object, but only its size.

## Units of Mass

Using a balance, you can measure the amount of matter an object contains. Mass is measured in kilograms (kg), although smaller masses are often measured in grams (g). In order to determine an object’s mass, you must place the object on one side of the scale and then add weight to the other side until the scale balances. The weight required to balance the scale is equal to the object’s mass.

In physics, mass is a property of matter and an object’s resistance to change in speed or position when a force is applied. It is not to be confused with weight, which is the downward force exerted on an object due to gravity.

The kilogram is the base unit of mass in the International System of Units. It is a solid cylinder of platinum and iridium kept in a vault along with six official copies at the International Bureau of Weights and Measures in Sevres, France. Until 2019, the kilogram was defined by comparing it to the physical prototype, but a new definition is planned that will fix its value to an invariant of nature.

## Calculating Mass

Mass is the quantitative measure of inertia, an object’s resistance to change in its speed or position given a net force. It is defined as the ratio of an object’s density to its volume. It can be calculated by using Newton’s second law, F = ma, where “F” is the force applied to an object and “m” is its mass.

Although mass and weight are often used interchangeably, they are not the same. While mass represents the amount of matter in an object, weight depends on the gravitational acceleration of that matter. Gravitational acceleration changes based on location, so an object’s weight can vary significantly between Earth and the Moon, for example.

In order to calculate mass, the most common method is to use a balance. A balance is a type of scale that subtracts an object’s container and sample from its total mass to determine its value. It is also possible to use a device that measures an object’s acceleration to determine its mass, using the formula mass = force * acceleration.

## Using a Balance

Using a balance to measure mass is an important skill in the lab. These expensive instruments are often delicate and require special care. Always be certain that the instrument is completely clean and on a firm surface. Never place a chemical directly on the balance pan; instead use a weigh boat or weighing paper. Weigh boats can be placed in a microfuge tube, a small vial, or a weighing cylinder to protect the balance from chemicals that could damage it. Depending on the type of work being done, you may need to also use a spatula for manipulating the sample.

When the balance is set up, it must be tared to zero by pressing the labeled button or pressing a tare bar. Zeroing the balance removes any remaining residue from the instrument, which will allow it to be more accurately measured. Be sure the tare value is written down, especially when using a hygroscopic substance (one that takes up moisture). If the balance has doors, be sure they are closed; air movement affects the accuracy of mass measurements.

## Calibration

Calibration is the process of using standard, traceable, calibrated tools to compare and test the output signal of a device to identify any deviation from the expected signal. This teaches the instrument how to better produce accurate results by establishing a relationship with these known values.

High precision mass measurements can be performed by comparing the weight of a sample to a stainless steel calibration standard. The conventional mass, or true mass, is reported, along with an uncertainty that establishes a probable universe within which the true value lies (this is analogous to the measurement error that would be present on a laboratory balance).

Internal calibration is generally more accurate than external calibration due to its ability to correct for differences in instrument parameters and space charge effects. The use of cluster ions as internal calibrants may be challenging for some instruments, however, because their m/z signals are often close to those of the analyte and will cause overlapping ion peak assignments.

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