Using a Digital Scale for Science Experiments
RATIONALE FOR WEIGHING
It is extremely important to accurately measure substances used in science experiments. However, this can be challenging since some of those substances will be solids and some will be liquids. When measuring solids, such as powders, particles can settle with varying amounts of air between them. When measured by volume (using spoons or measuring cups) the actual amount measured can vary. In addition, when measuring liquids, portions of the solution are lost each time the fluid is transferred from one container to another. For these reasons it becomes essential to use a digital scale to measure ingredients by weight rather than by volume. Still, it is important to follow specific steps to ensure the accuracy of measurement when using a scale.
FAMILIARIZE YOURSELF WITH THE SCALE
Every scale will vary in its physical appearance, but all share some common features.
Locate the following items on your scale before attempting measurements:
a. ON/OFF button or switch– turns power on and off; usually restores scale to default settings
b. Digital display– screen where the numbers will appear
c. MODE button– used to change units in which measurement will display (e.g., grams or ounces)
d. TARE/ZERO button– will "zero" the scale, recalibrating the weighing surface even when the surface is occupied with a container or test tube
e. Platform– flat or rounded surface where items are placed to be weighed
USING THE SCALE
1. Ensure that the scale is situated on a flat surface.
2. Turn the scale ON and press the MODE button to select desired unit of measurement.
3. Place a measuring beaker or test tube on the scale, using a stand if necessary.
4. Press the TARE/ZERO button to recalibrate the weight to zero before adding any substances. (NOTE: IF THE SCALE WILL NOT ZERO, THE SURFACE MAY NOT BE COMPLETELY FLAT.)
5. Add first substance amount as indicated by experiment directions.
6. Press the TARE/ZERO button to recalibrate the weight to zero before adding any additional substances. (NOTE: USING THE SCALE THIS WAY, YOU WILL NOT NEED TO "ADD UP" WHAT THE INDIVIDUAL SUBSTANCES WEIGH, WHICH SHOULD REDUCE EXPERIMENT ERROR ASSOCIATED WITH MISCALCULATIONS.)
LONG–TERM CARE
1. It is usually best to weigh substances using an appropriate vessel rather than placing them directly on the platform. This will reduce mess and potential interaction between substances and the scale's surface.
2. Always return scales to appropriate storage area with the power turned off to conserve batteries.
3. To ensure calibration is accurate, zero scale and place a weight of known amount on the platform. Repeat process, comparing actual weight amount with scale displayed amount. If there is a discrepancy, notify the teacher.
