Balance Lab

Topics: Mass, Weight, Force Pages: 7 (1933 words) Published: October 9, 2012
Balance Lab of a Copper Slug and Sodium Chloride (NaCl)
on a Centigram and Electronic Scale

PURPOSE/INTRODUCTION
The purpose of this experiment is to learn how to weigh a substance on a centigram scale and an electronic scale through direct weight or by weight difference. The hypothesis is that all scales used should show the same weight for a given sample. The experiment should show precision and accuracy of the equipment being used. This will allow a better understanding on how to properly weigh a given sample and what scale is more accurate. The following are definitions of terms used:

Precision refers to the closeness of the set of values obtained from identical measurements of a given quantity.
Accuracy refers to the closeness of a single measurement to its true value. To determine the difference between two measurements the following formula was used:
Δ Weight = Weight A – Weight B(1)
To determine the average of all the weights the following formula was used:
a = ∑X1 + X2 + X3 +…XnXn(2)

MATERIALS
Materials required to test the hypothesis in a lab include:
*
* Centigram Balance (Qty. 2)
* Electronic Balance (Qty. 1)
* Beaker, 100 mL (Qty. 1)
* Watch Glass (Qty. 1)
* Copper Slug (Qty. 5)
* Unknown Mass (Qty. 1)
* Sodium Chloride (1.0 to 1.2g)

METHOD
Part One: To find the direct weight of an object using a centigram balance. Use centigram balance #1. Clean the platform with a lint free cloth and check that all weights on the beams are in the zero position. Check to make sure that the centigram beam indicator aligns with the arrow on the stand. If zero, place object in the center of the platform and move beam weights until the beam indicator realigns with the arrow. Record the weight measurement.

Figure 1 – Centigram balance with copper slug
Repeat directions for part one on centigram balance #2 using the same object and record the weight measurement. Part Two: To find the weight of an object by difference using a centigram balance. Use centigram balance #1. Clean the platform with a lint free cloth and check that all weights on the beams are in the zero position. Check to make sure that the centigram beam indicator aligns with the arrow on the stand. If zero, place a clean and dry 100 mL beaker in the center of the platform and move beam weights until the beam indicator realigns with the arrow. Record the weight measurement.

Figure 2 – Centigram balance with empty 100 mL beaker
Add object to the 100 mL beaker and move the beam weights until the beam indicator realigns with the arrow. Record the weight measurement.

Figure 3 – Centigram balance with 100 mL beaker and copper slug Repeat directions for part two on centigram balance #2 using the same beaker and object. Record the weight measurements. Part Three: To find the direct weight of an object using an electronic balance. Clean the platform on electronic balance with a lint free cloth. Check that the scale indicates a zero reading. If zero, place object in the center of the platform and record the weight measurement.

Figure 4 – Electronic balance and copper slug
Part Four: To find the weight of an object by difference using electronic balance. Clean the platform on the electronic balance with a lint free cloth. Check that the scale indicates a zero reading. If zero, place a clean and dry 100 mL beaker in the center of the platform and record the weight measurement.

Figure 5 – Electronic balance with 100 mL beaker
Add object to the 100 mL beaker and record the weight measurement.

Figure 6 – Electronic balance with 100 mL beaker and copper slug Part Five: To find the average weight of an object using electronic balance. Clean the platform on electronic balance with a lint free cloth. Check that the scale indicates a zero reading. If zero, place object in the center of the platform and record the weight measurement. Leaving the first object on platform; add a second identical object...