Experiment No. 3 CONSTANT WEIGHING OF UNKNOWN SAMPLE PDF

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NAME: Arien Jean M. Lopez COURSE & YEAR: BSF – 1

SUBJECT: CHEM 113 DATE PERFORMED: November 6, 2018

Experiment No. 3 CONSTANT WEIGHING OF UNKNOWN SAMPLE INTRODUCTION Constant refers to and is a property of anything which remains the same. And weight is the A substance or anything has its own innate weight it might be diminutive or enormous but if it is exposed to air it is highly vulnerable to moisture whereas it added up to the true and constant weight of the substance. If a partially solid sample that also contains some volatile material is heated, the weight of the sample will decrease because some of the volatile material will be driven into the atmosphere and will not return to the sample is cooled again. If the weight of the sample is documented subsequently in each interval of heating and cooling, sooner or later the sample will grasp a weight that no longer variates upon additional heating, demonstrating that all of the volatile material in the sample has been rid off. This is called heating the sample to constant weight and is often used when analyzing moist solids such as soil or biological materials, water being the volatile material in these instances. (Science Answers, 2017) OBJECTIVES 

Learn to determine the constant weight of an unknown sample



Be familiar of handling samples avoiding moisture.



Acquaint on how to use properly the diseccator.

METHODOLOGY

This section incorporates the series of actions taken to the conducted experiment. This experiment primarily intents to present the determining of the constant weight of a substance as essential practices evaluating humid objects, in the interpretation and evaluation of analytical data. In the first place, the experimenter obtained the unknown sample and then secured three (3) crucibles with cover. Later, the analytical balance was calibrated and after that the initial weight of the crucibles and noted it down. Afterward, prepare the oven and heat the weighted crucibles at 110 0C for one (1) hour. Subsequently, the crucibles transferred in a diseccator and ajar it for five (5) minutes; and then let it cooled down for thirty (30) minutes. And then again, carefully the weight is taken and recorded. After that, to determine if the crucibles was at their constant weight the difference of the two consecutive weights were computed and if it reached at 0.0005g below then it is already on its constant weight; if not the crucibles were heated again until the difference of the 2 successive weights is at 0.0005g or lesser. After ensuring the constant weight of the crucibles, place 2g of the unknown sample each crucible and then again determine its constant weight throught repeating the heating, cooling and weighing procedures and computing the difference 2 consecutive weights and obtaining 0.0005g or smaller result.

RESULTS AND DISCUSSION

Revealed on this section the results and discussion attained from the operated experiment. As part of the method for the determination of the constant weight of an unknown sample it will be required to precisely ascertain the empty weights of a set of crucibles. They are then cooled and weighed. This process of heating and cooling is repeated until successive weighings agree to within 0.5mg, ensuring that it already possess its constant weight. (de la Camp & Seely, 2013) The crucibles are renamed with T1, T2 and T3 whereas its weights were recorded and computed which is exhibited by Table 1 below. Table 1. Computation of Constant Weight of the Crucibles Crucible T1

Computation of Constant Weight 1st weight – 2nd weight 34.1554g - 35.9528g = - 1.7974g 2nd weight – 3rd weight 35.9528g - 35.9520g = 0.0008g 3rd weight – 4th weight 35.9520g - 35.9516g = 0.0004g

T2

1st weight – 2nd weight 27.8196g - 27.8179g = 0.0017g 2nd weight – 3rd weight 27.8179g - 27.8170g = 0.0009g 3rd weight – 4th weight

T3

27.8170g - 27.8165g = 0.0005g 1st weight – 2nd weight 29.7528g - 29.7518g = 0.0010g 2nd weight – 3rd weight 29.7518g - 29.7510g = 0.0008g 3rd weight – 4th weight 29.7510g - 29.7507 = 0.0003g

It is very noticeable on the calculated results that there are some disturbing unstabilities of the weights of the crucibles, which is evidently displayed on the context of T1 crucible which initially weighs 34.1554g but then after it undergoes heating, cooling it weighs increased to

35.9528g. The experimenters believe that the cover might interchanged with other group’s crucible which is one of the common systematic errors committed while conducting an expirement. But eventually, seeking the constant weight of the rest of the crucibles came nearly efficient as the diffences of the two consecutive weighs landed at 0.0005g or lower, meaning the crucible is ready to be stored with an unknown substance, which was also heated, cooled and weighed to its constant weight and the following data are displayed on Table 2. Table 2. Computation of Initial Weight of the Crucibles with the Unknown Sample (Ammonium Sulfate) Crucible Constant Weight Amount of the Total Initial Weight W/out Unknown Unknown Sample (g) Sample (g) placed (g) T1 35.9524 2.1986 38.1510 T2 27.8165 3.0980 30.9145 T3 29.7507 2.1141 31.8648

The initial weight of the unknown sample stored in the heated crucible was still apparently has its acquired moisture, in order to find the constant weight of the unknown sample it was undergone also series of heating, cooling and weighing. The sum of the constant weight of the crucible and the amount of the placed unknown sample (ammonium sulfate) is the recorded initial weight of the filled crucible. Table 3. Computation of Constant Weight of the Crucibles Crucibles Computation of the Constant Weight 1st weight – 2nd weight T1 38.1510g – 36.8501g = 1.3009g 2nd weight – 3rd weight

T2

36.8501g - 36.8497g = 0.0004g 1st weight – 2nd weight 30.9145g – 29.8521g = 1.0624g 2nd weight – 3rd weight 29.8521g - 29.8513g = 0.0008g 3rd weight – 4th weight 29.8513g - 29.8508g = 0.0005g

1st weight – 2nd weight

T3

31.8648g – 31.0732g = 0.7916g 2nd weight – 3rd weight 31.0732g - 31.0725g = 0.0007g 3rd weight – 4th weight 31.0725g - 31.0723g = 0.0002g

Getting the constant weight of the crucibles filled with unknown samples were very difficult due to the fluctuations of the conditions present on the laboratory and the susceptibility of the crucibles and the sample regarding proper handling. Fluctuations of the weight occur and evidently shown on some point of the data documented. Since during the conduct of the experiment rotational blackout bothered a lot the process of the laboratory activity since equipment used were electricity-dependent. But nevertheless, the constant weight of the unknown sample which is ammonium sulfate were still managed to be figured out though there are a lot of errors carried out by the expirementers that might lead to uncertainties and erroneous results. Shown on Table 4 is the deciphered constant weight of the unknown samples from the constant weight of crucible with the unknown sample minus the constant weight of the 3 crucibles. Table 4. Computation of Constant Weight of the Unknown Sample (Ammonium Sulfate) Crucible

Constant Weight of the Crucible Contained w/ unknown sample (g)

Constant Weight W/out Unknown Sample (g)

Constant Weight of the Unknown Sample (g)

T1 T2 T3

36.8497 29.8508 31.0723

35.9524 27.8165 29.7507

0.8973 2.0343 1.3216

CONCLUSION In order to extricate the amount of the moisture present on the unknown sample which is ammonium sulfate, the initial weight and the constant weight substantiated upon the conduct of

experiment is compared seen on Figure 1. Where the distinguishable interval between the weight of the unknown sample (ammonium sulfate) before it was contacted with the heat and after it undergone heat has been demonstrated. Thus, the possibility of having great amount of moisture on the sample is fairly significant.

In itia l an d Co n sta nt Wei g ht o f t h e Un k n o w n S am p le Constant Weight

0.9

1.32

2.11

2.03

2.2

3.1

Initial Weight

T1

T2

T3

Figure 1. Comparison of Initial and Constant Weight of the Unknown Sample (ammonium sulfate)

Some circumstances were noticed by the experimenters which confided from the laboratory notes shared by de la Camp & Seely, that “if a crucible is not at the temperature of the balance compartment it will likely show a weight different from that it would show were it at

the same temperature”. Moreover, if it is warmer the weight will be to some extent less, if cooler somewhat more in arrears to the making of convection currents which disturb the apparent mass. Furthermore, the compact discovered here is within that which is routinely observed for two separate balances and this cooling sequence took place outside the dessicator. The amount of time necessary to achieve thermal equilibrium with the environment will likely be somewhat longer when you let the crucible cool in the dessicator. (de la Camp & Seely, 2013) Entirely, finding the constant weight of any substance or sample is very crucial in conducting an experiment since the it is were the accuracy of the weight is dependent. In observing the necessities in getting the constant weight of a sample, one of these is the proper handling is a must obeyed principle where the exposure of the sample to moisture must be prohibited. Another, is the availability and the accurateness of the equipment used such as the oven and the analytical balance where some unexpected conditions might occur for instance the incidence of blackout which hamper the accessibility of electricity that deteriorates the process of the procedure of the laboratory activity regarding the use of equipments, and the appropriate recording and keeping of data from the operated experiment. Nonetheless, the need of the accurate constant weight is very impeccable principle to be successful and certain in chemistry.

REFERENCES De la Camp & O. Seely (2013) Heating a Crucible to Constant Weight - Chemistry LibreTexts ,California

State

University

Dominguez

https://chem.libretexts.org/Demos%2C_Techniques

Hills,

retrieved

at

%2C_and_Experiments/General_Lab_Techniques/Heating_a_Crucible_to_Constant_Wei ght Answers.com (2017) What does it mean to heat a sample to constant weigh, retrieved at http://science.answers.com/Q/What_does_it_mean_to_heat_a_sample_to_constant_weig ht

APPENDICES The following tables shown are data that are gathered during the conducted experiment where the weight of the empty crucible and the crucible filled with unknown sample (ammonium sulfate) were recorded to decipher its constant weight. Appendix 1. Initial weight without contact to heat Crucible T1 T2 T3

Weight (g) 34.1554 27.8196 29.7528

Appendix 2. 2nd weight with contact to heat (110 0C for 1hr) Crucible T1 T2 T3

Weight (g) 35.9528 27.8179 29.7518

Appendix 3. 3rd weight with contact to heat (110 0C for 1hr) Crucible T1 T2 T3

Weight (g) 35.9516 27.8165 29.7510

Appendix 4. 4th weight with contact to heat (110 0C for 1hr) Crucible T1 T2 T3

Weight (g) 35.9524 27.8175 29.7507

Appendix 5. Initial weight without contact to heat with unknown sample (ammonium sulfate) Crucible Weight (g) T1 38.1510 T2 30.9145 T3 31.8648 Appendix 6. 2nd weight with contact to heat with unknown sample (ammonium sulfate) Crucible Weight (g) T1 36.8501 T2 29.8521 T3 31.0732

Appendix 7. 3rd weight with contact to heat with unknown sample (ammonium sulfate) Crucible Weight (g) T1 36.8497 T2 29.8513 T3 31.0725 Appendix 7. 3rd weight with contact to heat with unknown sample (ammonium sulfate) Crucible Weight (g) T1 ------T2 29.8508 T3 31.0723...