Weighing is an important part of laboratory analyses. By using proper procedures, you can eliminate many errors that may occur during weighing.
Start by assembling the proper equipment, such as containers for weighing, receiving vessels, forceps, pipettes and spatulas of the appropriate size. Make sure the containers selected are clean and dry.
Weighing by weight
Weighing by weight is the most common way to determine the mass of a sample. This method is accurate and easy to perform. However, you should use a clean, dust-free bench and keep the balance in a draft free location. Moreover, it is important to keep the balance in a stable position and avoid touching it with your hands. This is to prevent fingerprints from transferring onto the balance pan and to prevent any hygroscopic materials from absorbing water during weighing.
To weigh a sample, first place a piece of clean weighing paper on the balance pan and zero it to read 0 grams. Then place the beaker on top of the weighing paper and push the “taring” button. Now only the weight of the beaker will appear on the display. This is a very convenient way to weigh out chemicals, especially since analytical balances are very sensitive and can detect even tiny amounts of reagents.
Weighing by volume
Volume is the amount of space an object takes up, measured in cubic units such as meters, liters or milliliters. It is one of the derived quantities defined by the International System of Units, along with length, time and mass.
It is important to understand the difference between volume and weight. For example, a pound of feathers and a pound of lead will have the same volume, but they will not weigh the same. The reason is that the density of the lead is higher, and therefore it weighs more.
To measure the volume of a weight, you can use a graduated cylinder and a balance. Place the standard weight on the balance and then put the measured weight on top of it. After weighing, you can use the drying function to remove any residual liquid on the weight surface. This will improve the accuracy of the measurement.
Weighing by mass
The weighing process is an important step in many analytical procedures. However, it can be prone to errors. These errors can range from air currents to inaccurate calibration. It is important to understand these sources of error and to eliminate them.
In addition, the weighing environment must be free of corrosive chemicals and dust. The weighing balance should be maintained and calibrated regularly by an experienced service person. A good maintenance plan should include testing the calibration weights with a reference scale. This will ensure that the weighing equipment is accurate and can be trusted to produce reliable results.
Weighing by mass is an important method for determining the quantity of a sample. It is also a useful technique for measuring the density of an object. It is important to distinguish between mass and weight, though, since the latter describes a force that depends on gravity. An object’s weight will change if it is moved to a different location, but its mass will remain the same.
Weighing by difference
Weighing by difference is a simple, clean technique for weighing solids and some liquid components. First, a target mass is determined for the transfer of a solid from a weighing bottle to a beaker or volumetric flask. This is recorded in the laboratory notebook. Then the weighing bottle is tapped to within 10% of this value, and the mass transferred is recorded (to the nearest 0.0001 g).
A dry desiccator should be used for the storage of a solid. This is maintained at a standard dryness by a color indicator that turns pink when the desiccant has become exhausted.
A tared balance is required to reduce errors due to moisture pickup and changes in mass during weighing. This is done by pressing the Tare button, which sets the balance readout to 0.0000 g. A substance to be weighed is then added to the tared container that will hold it, never directly to the pan of an analytical balance.