Mass Determination

Objective:
The purpose of this experiment is to see the difference of precision of different balances. When doing experiments we determine the mass my measuring the sample with a balance. There are many kinds of balances that measure to different precisions. This experiment shows the different results that two balances can give. Summary of Procedures

Determine the mass with the triple beam scale to the most precise measurement possible for the scale. First we measure the mass of the beaker. We measure the beaker with the sample inside it and subtract the beakers weight. This will give us an accurate measurement of the sample. Repeat exercise with electronic scale. Figured out the difference in precision of the scales. Pre-laboratory Questions

What are the differences in meaning between mass and weight? IN the laboratory, do we determine the mass or the weight of objects? Mass is the measurement of matter of an object. Weight is the response of mass to gravity. The mass does not change with gravity but the weight does. In the laboratory we are measuring the weight of the sample since can’t measure its mass without gravity. Explain the following. Weigh approximately 5 grams of NaCl to the nearest milligram. The weight of 5 grams of NaCl is equal to 5,000 milligrams. We convert grams to milligrams by multiply grams by a 1,000. Data tables

Triple beam balance
Mass of empty beaker : 66.60 g
ID number of object Mass of beaker plus object Mass of object itself Sample 18-A 69.20 g 2.60 g
Sample 18-B 99.52 g 32.92 g
Sample 18-C 77.72 g 11.12 g
Electronic balance
Mass of empty beaker : 66.60 g
ID number of object Mass of beaker plus object Mass of object itself Sample 18-A 69.293 g 02.635 g
Sample 18-B 99.507 g 32.849 g
Sample 18-C 77.694 g 11.036 g
Difference in masses determined on the two balances
Id number of object Mass of object itself
Sample 18-A 0.04 g
Sample 18-B 0.07 g
Sample 18-C 0.08 g
Calculation
We determined the weight of the sample by measuring the beaker and subtracting the beakers weight from the weight of the beaker with the sample inside. The experiment is repeated in a different balance. To finish off the experiment we calculate the difference between the results of the balances. Example:

Beaker weight= Aweight of beaker with sample = B sample weight = C B-A=C
To determine the difference in weight that the two scales provide we use this formula X= sample of weight from triple beam Balance Y= sample of weight from electric Balance Z= Difference of results

Y-X = Z
Why is it important always to use the same balance during the course of an experiment? Different balances might display different results because they are not calibrated perfectly. Thus we must use the same balance throughout the experiment to get accurate results What error is introduced in a mass determination if the object being weighed is warm? Why? The sample could appear to weigh less. The air around sample will get hot and cause the sample to weigh less than it weight. Resulting in the balance giving an inaccurate result. Why should reagent chemicals never be weighed directly on the pan of the balance? The pan must be kept clean and at a constant weight. The chemicals must be prevented from being mixed together.