Using the correct methods when weighing samples helps reduce error. Errors can be caused by environmental factors such as air currents, balance drift and thermal equilibrium between the test sample and the reference standards.
The substance being tested should always be added to a tared container rather than directly to the pan of the analytical balance. This helps prevent the substance from sticking to the weighing paper and producing an error in the reading.
Mass
Weighing solids and liquids is a common laboratory practice. It is used to measure ingredients for chemical reactions, determine yields, and ensure the proper proportions of solute and solvent in solutions. In addition, weighing is important for the safety and accuracy of chemical procedures.
Although the terms mass and weight are often used interchangeably, they are not the same. Mass is the quantitative measure of an object’s inertia in changing its speed or position upon application of a force, while weight is the result of an object’s gravitational attraction.
The best way to accurately measure mass is with a balance, also known as a beam balance or center of gravity balance. This instrument consists of a pivoted horizontal lever with arms of equal length – the beam – and a weighing pan suspended from each arm. The unknown mass is placed in one of the weighing pans, and standard masses are added to the other weighing pan until the beam comes into balance.
Weight
Weighing is used to determine the amount of substance needed for chemical reactions and other laboratory tasks. Good laboratory techniques and practices are important for obtaining accurate weight measurements. Errors can occur from a variety of sources, including balance drift, air currents, lack of thermal equilibrium, and manipulations of the instrument.
It is important to remember that mass and weight are not the same. In general, a more massive object will have greater weight than a less massive object. This is because a mass has inertia and, therefore, an inertial force acting on it. Weight, on the other hand, is a vector quantity and has direction as well.
When using a top loading balance, it is important to use a piece of weighing paper that is large enough to cover the entire pan surface. This prevents the sample from sticking to the weighing paper and causing inaccurate measurements. Additionally, it is important to use a spatula of an appropriate size when placing the sample in the pan.
Volume
Volume is the size of an object or substance in terms of length x width x height. It is usually measured in cubic units, though the British (customary) system uses barrels, bushels, gallons and pecks, and the International system commonly uses litres.
Measuring the volume of a solid is relatively simple. The object is placed inside a container that has an exact volume measurement, such as a graduated cylinder. Then, water is poured into the container until it reaches the same level as the object itself. The reading on the scale is then the object’s volume.
This method can’t be used for corrosive or oxidizing samples such as potassium permanganate K2MnO4 or metallic sodium, which react with water. These must be weighed in a sealed container to prevent chemical reactions. It’s also important to ensure that the weighing pan is clean and free of dust or other substances that can affect the readings on the balance.
Temperature
The temperature of a material or space can be measured using modern scientific thermometers and scales. Temperature is a thermodynamic quantity representing the average microscopic kinetic energy of particles in a system. It is an intensive property, as opposed to volume and pressure, which are extensive properties.
A fine powder can generate a large static charge that must be eliminated before weighing. For this reason, a weighing funnel is usually preferred for these applications. The solid can also be weighed directly into preweighed or tared volumes of the appropriate size.
Vibration can cause the weighing system to drift or make false readings. To minimize this effect, the weighing system should be isolated from vibration sources and balanced on a rigid surface, if possible. Large temperature changes can cause the weighing vessel to expand or contract, which can result in an inaccurate weight measurement. To compensate for this, the weighing system should be installed with load cells and mounting hardware that can handle the expansion and contraction of the weighing vessel.