Objective
Main objectives of this lab are:
learn and practice to use a graduated cylinder, pipet, and buret for volume measurements;
determine average volume of a water drop using volumetric ware;
find the density of liquid and a solid using mass and volume measurements.
Hypothesis
Average percent difference indicates volumetric ware’ accuracy and precision. In this lab pipet out of all volumetric ware will have the highest accuracy and precision and, therefore, lowest average percent difference.
Materials
In this lab, the following materials were used:
graduated cylinders;
beakers;
burets;
plastic droppers;
pipets;
rubber stoppers;
unknown liquids.
Procedure
The graduated cylinder
The graduated cylinder was obtained, and a 50-mL beaker was weighed. Using a wash bottle, exactly 10.0 mL of distilled water were added to the cylinder. Water from the cylinder was poured into a beaker, and the beaker with water was weighed on the same scales. Another 10.0 mL of distilled water were added to the cylinder and poured into a beaker. Masses of the empty beaker and the beaker containing 10.0 mL and 20.0 mL were recorded.
The Pipet
A 10-mL pipet was obtained, and a clean, dry empty 50-mL beaker was weighed. Using a suction bulb, 10 mL of distilled water were drawn into a pipet (exactly to the mark) and poured into the weighed 50-mL beaker. The beaker containing 10.0 mL was weighed. Another 10.0-mL sample of water was poured into the beaker using the pipet and a suction bulb. The beaker was weighed again, and the weights of the beaker containing no water, 10.0, and 20.0 mL of distilled water were recorded.
The Buret
A buret was obtained, mounted on a ringstand, and filled with distilled water. A dry 50-mL beaker was weighed. Two samples of water were added to the beaker from a buret weighing the beaker after adding each sample. Buret readings and beaker weights were recorded.
The Volume of a Drop
20 mL of distilled water were added to a 50 mL beaker. Using a vertically held plastic dropper, 25 drops of distilled water were added to a graduated cylinder. The cylinder reading was recorded. Without emptying the cylinder, additional 25 drops were added to it and volume reading was recorded. After emptying the cylinder, the same procedure was performed holding the dropper horizontally. After that, the same procedure was repeated twice using a buret to deliver drops.
Density of an Unknown Liquid
The 30-mL sample of an unknown liquid was obtained, and its identification number was recorded. A clean, dry 50-mL beaker was weighed, and its weighed was recorded. A pipet was rinsed with an unknown liquid and used to deliver 10.00 mL of unknown liquid into the beaker. The beaker containing unknown liquid was weighed, and another 10.00-mL sample was added to it using a pipet. After that, the beaker’s weight was recorded again.
Density of a Solid
The weight of a dry clean 50-mL beaker was recorded. A rubber stopper was obtained and placed in a beaker; their combined weight was recorded. A graduated cylinder was filled approximately halfway with distilled water, and the volume reading was recorded. A rubber stopper was put into the cylinder without making any splashes, and new volume reading was recorded.
Results
The Graduated Cylinder
Raw data of the experiment measurements is presented in Tab. 3.1:
Volume of water added to a beaker on a mass basis can be found:
Vmass basis=mbeaker+sample-mbeaker=69.9g-60.3g=9.3g
Volume on a mass basis of a second sample can be found the same way. Having volumes of the same samples on a reading and mass basis, volume difference can be calculated:
Difference=Vreading basis-Vmass basis=10.0mL-9.3mL=0.7mL
Having average volume difference, average % difference can be computed using the following formula:
%Difference=Average differenceV(reading basis)100%=-0.5510.0100%=-5.5%
All the calculations are summed up in Tab. 3.2:
The Pipet
The calculations for the pipet average % difference are the same as for the graduated cylinder. Raw data is presented in Tab. 3.3, and the results of calculations are shown in Tab. 3.4:
The Buret
Calculations for the buret average % difference are the same as in the previous cases of the pipet and graduated cylinder. Raw experimental data is shown in Tab. 3.5, and results of the calculations are presented in Tab. 3.6:
The Volume of a Drop
Initial data on the experiment is shown in Tab. 3.7:
The volume of drop can be obtained by dividing the total volume of water by the number of drops:
Vdrop=V(total)N(drops)=1.2 mL25=0.04 mL
Calculations are summed up in Tab.3.8:
Volume of a single drop can be found graphically from the slope of the Total Volume vs. Number of drops graph:
Figure 3.1 Total Volume vs. Number of Drops Graph
Density of an Unknown Liquid
Raw data from this experiment is shown in Tab. 3.9:
Density of an unknown liquid can be found using the following formula:
d=mV=10.5 g10 mL=1.05 g/mL
Results of calculations are summed up in Tab. 3.10:
Density of a solid
Raw data is presented in Tab. 3.11:
The density of the rubber stopper can be found similarly to the density of an unknown liquid – its volume and mass are required. Mass of the stopper:
mstopper=mbeaker+stopper-mbeaker=69.52g-60.35g=9.17g
Volume of a stopper can be found as a difference between graduated cylinder readings:
Vstopper=Vbeaker+stopper-Vbeaker=30.0mL-25.0mL=5.0mL
Having all the necessary values, density of the rubber stopper can be found:
d=mV=9.17g5.0mL=1.83 g/mL
Results of the calculations are shown in Tab. 3.12:
Summary
Primary results of the lab can be summarized in the Tab. 3.13:
Conclusion
In this lab we have learned and practiced to use volumetric ware, we determined average volume of a water drop, and used mass and volume measurements to determine density of liquid and a solid. Average percent difference indicates volumetric ware's precision and accuracy, according to our measurements the pipet possessed the best accuracy with 0.2% average percent difference. The volume of the average drop of water comprised 0.058 mL. Unknown liquid’s density was 1.05 g/mL, and the density of a rubber stopper comprised 1.83 g/mL.
Works Cited
Slabaugh, Michael R, and Spencer L Seager. Safety-Scale Laboratory Experiments For Chemistry For Today. Pacific Grove, Calif.: Brooks/Cole, 2013. Print.
