General Chemistry Lab Report 1 PDF

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General Chemistry 1 SCC201.641B Afsana Abdul Rahim Lab Partner: Lamia Hauter Experiment 1: Measurements and Significant Figures

09/16/2017 Professor Shashikanth Ponnala

Objectives: 

To learn how to correctly read scales and report measurements with the correct number of significant figures.



To correctly report significant figures in the results of calculations involving measurements.



To evaluate and express accuracy and precision in measurements by comparing true values to measured values.



To represent calculated data using graphs.

Materials required: 

Distilled Water (dH O)



Alcohol Thermometer



Analytical Balance



Dropper



50 mL Graduated Cylinder



25 mL Graduated Cylinder



150 mL Beaker



50 mL Beaker



10 mL pipet

2

Methods: Part A: Density of Water 

An empty, clean and dry 50 mL graduated cylinder was weighed on the balance and the mass of the cylinder was recorded.



10 mL of distilled water was poured into the graduated cylinder; approximately 9 mL of water was initially poured into the cylinder and then a dropper was used to add water up to the 10.0 ml mark. The meniscus rested on the mark.



The cylinder containing the water was weighed and the mass was recorded.



Distilled water was added to the cylinder until the meniscus was around the 29 mL mark. Then a dropper was used to add water up to the 30.0 mark. The cylinder was weighed and the mass was recorded.



The same procedure from step 2 and 4 was done to add water to the 50.0 mL mark. The cylinder was weighed and the mass was recorded.



The mass of the water was determined by subtracting the mass of the empty 50 mL graduated cylinder from the mass of the cylinder containing the water at 10.0 mL, 30.0 mL, and 50.0 mL.



The density of water was calculated by using the formula density = mass/volume.

Part B: Accuracy and Precision of Volumetric Devices 

100 mL of distilled water was poured into a 150 mL beaker. The temperature of the water was measured using an alcohol thermometer.



An empty, clean and dry 50 mL beaker was weighed using the balance. The mass of the beaker was recorded.



10 mL of distilled water was measured using a 25 mL graduated cylinder (using the same technique from part A) and was poured into the 50 mL beaker.



The beaker with 10.0 mL of water was weighed and the mass was recorded.



The mass of water was determined by subtracting the mass of the empty 50 mL beaker from the mass of the beaker and 10 mL of water.



Steps 2-5 were repeated two more times to obtain multiple trials of data.



Steps 2-6 were repeated with a pipet that measured 10.0 mL of water.



The average mass of the water measured using the graduated cylinder and the pipet were calculated and recorded.



The true value for mass of 10.0 mL of water at measured temperature was given to me 9.981g.



The % error in the average mass of samples from the graduated cylinder and pipet were calculated using the true value of the mass.



The deviation from the average mass for each sample was calculated.

Data and Calculations: Table 1: Density of water 10.0 mL

30.0 mL

50.0 mL

Mass of empty 50 mL graduated cylinder Mass of cylinder + water

23.875 g

23.875 g

23.875 g

33.749 g

53.657 g

73.595 g

Mass of water

9.874 g

29.782 g

49.720 g

Density of water sample

0.987 g/mL

0.993 g/mL

0.994 g/mL

Calculations: This shows the calculation of the mass of water and the calculation of the volume 30 mL in a 50 mL graduated cylinder and we perform the density formula as shown below for other volumes. Furthermore, Density is the amount of mass in a unit volume of a substance (Brown 19).

Mass of water = (Mass of cylinder + water) – Mass of empty 50 mL graduated cylinder = 53.657 g –23.875 g = 29.782 g

Density =

Mass Volume

Density =

29.782 g 30.0mL

Density = 0.993 g/mL

Figure 1: Density of Water in the Graduated Cylinder 1

Density of Water

0.99

0.99 0.99

0.99 0.99 0.99 0.99 0.99 0.98 0.98 10

30

50

Volume/mL

Table 2: Accuracy and precision of volumetric devices

Temperature of water Mass of empty 50 mL beaker Mass of beaker +

Graduated Cylinder (10.0 mL) 22C 29.677 g 39.152 g

Pipet (10.00 mL) 22C 29.677 g 39.666 g

38.961 g

39.644 g

Trial 1

10 mL water

Trial 2 39.221 g

39.609 g

9.475 g

9.989 g

9.284 g

9.967 g

9.544 g

9.932 g

9.434 g 9.981 g

9.963 g 9.981 g

5.48%

0.18%

Graduated Cylinder (10.0 mL) 0.041 g

Pipet (10.00 mL) 0.026 g

0.15 g

0.004 g

0.11 g

0.031 g

0.1003 g

0.0203 g

Trial 3 Trial 1 Mass of 10 mL water

Trial 2

Trial 3 Average mass of 10 mL water True value for mass of water at measured temperature % Error in average mass of water

Trial 1 Trial 2 Deviation from Trial 3 average mass Average deviation Calculations:

This shows how the calculations were determined in the experiment. The data used was obtained using the 10.0 mL graduated cylinder for measuring the water. The true value of mass of water at temperature of 22C was given by instructor from reference source chemicals which is 9.981g.

Mass of 10 mL of water = (Mass of beaker+10 mL water) - Mass of empty beaker = 39.152 g – 29.677 g = 9.475 g

Average mass of water (experimental) =

=

(value 1+ value2+value3) Number of values (9.475 g+9.284 g+9.544 g) 3

= 9.434 g

% Error in average mass of water =

=

(true value−experimental value) true value (9.981 g−9.434 g) 9.981 g

X 100

= 2.1308%

Deviation from average mass = Deviation of value i = average value – value i = 9.434 g – 9.475 g  = 0.041 g

Average deviation =

=

(deviation of value 1+ deviationof value 2+deviation of value 3) Number of values

( 0.041+ 0.15 + 0.11 ) g 3

= 0.1003 g

Discussion: All matter has certain characteristics that may or may not change depending on the quantity matter present. These characteristics of matter are called properties. Properties can be chemical is how the substance changes at a molecular level, thus can only be observed when a substance is changed to another substance. Also, it can be physical which there is no change in the identity of the object and can be observed or measured without changing the composition of matter,

however, it may look or feel different. Properties of matter are further divided into subcategories, extensive and intensive properties. Intensive properties do not depend on the amount of the substance present; for example, intensive properties remain same for 1 gram (g) or 1 kilogram (kg) of the substance. Extensive properties on the other hand depend on the amount of substance being tested or observed. Mass and volume of a substance are always extensive properties (Brown 11). Mass is the amount of matter in a sample and volume is the amount of space that a sample occupies. Measured numbers always have some degree of uncertainty. Measurement devices are limited by how they are calibrated and measured values are subject to different interpretations by different individuals. The key factors of these experiments were accuracy and precision. Accuracy is measurement to proximity of a measurement to the true value and precision is related to the measurement of several values between each other (Miller 17). Accuracy and precision of data recorded is a foundation of chemistry and all experiments. In the first part of our experiment was to determine the density of water based on our calculations, the mass of water increased depending on the volume (10.0mL, 30.0mL, and 50.0mL) that was utilized. For instance, the mass of the empty 50 mL beaker was 23.875 g which was measure by analytical balance. Also, the results show the mass of water within the three volumes. The mass of 10mL water was measured to be 9.874 g and the density was 0.987 g/mL. To include, the mass of water increased to 29.782 g in a volume of 30.0 mL, the density was 0.993g/mL. Lastly, the volume of 50.0 mL mass of water was 49.720 g, and the resulted density was 0.994 g/mL. Based on the results of the density there were some slight fluctuations, but the values had precision which means this shows some intensive properties. Intensive properties are independent of the amount of the substance that is present. To state this it is required to perform another experiment.

As discussed earlier, the density of a substance depends on and changes with the change in its mass and/or volume. The density of water increased slightly as the volume of water being tested was increased. In the second experiment, the water was measured using a 10.0 mL graduated cylinder and a 10.00 mL pipet. Here, the temperature of the water was recorded to be 22C. The experimental average mass of water was then compared to the known mass of water at measured temperature. These values were precise but not accurate. There was found to be a 5.48 % error and 0.1003 g of average deviation when a 10.0 mL graduated cylinder was used to measure volume of water. Average deviation of 0.0203 g and 0.18 % error was recorded in the data when the 10.00 mL pipet was used to measure the volume of water. Errors: There are several factors that could have reduced the precision and accuracy of the results such as: 

Human error when reading the scale incorrectly and inappropriate prepping of the instruments used. The pipet has finer calibration marks than the graduated cylinder so it was more accurate and precise than the graduated cylinder.



Factors such as the scale not being calibrated correctly, residual water droplets in the measuring devices from previous measurements etc. should be considered for the errors in the experiment.

Conclusion: It is observed in the experiment that the density of a substance changes as the mass and volume of the substance are changed. Mass and volume are extensive properties. Density is an intensive property. The density of water remained relatively constant even though the amount of water in the samples varied in the first experiment. As the volume of the water being analyzed for density

was increased from 10.0 mL to 30.0 mL to 50.0 mL, the density of the samples increased from 0.987 g/mL to 0.993 g/mL to 0.994 g/mL as shown in Table 1. The graduated cylinder had an average deviation of 0.1003 g and the pipet had an average deviation of 0.0203 g as shown Table 2. The pipet was more precise because it had smaller deviation compared to the graduated cylinder. The percentage error for the graduated cylinder was 5.48%. The pipet is more accurate because it had the lower percentage error which was 0.18% as shown Table 2. References: Miller, D. Measurement and Significant Figures. In SCC201 General Chemistry Laboratory Manual (pp. 15-19). Dubuque: Kendal Hunt. 2013. Print. Brown, Theodore L., H. LeMay Eugene, and Bruce Bursten Edward. Chemistry: The Central Science. 14th ed. Upper Saddle River, NJ: Prentice Hall. 2014. Print....