Jonathan O’Donnell
CHM 3120C
05/15/2014
TA: Darrell Cerrato
Lab 1. Volumetric Glassware Calibration
Introduction:
This experiment is designed to educate proper techniques for using an analytical balance and volumetric apparatus’s. Accuracy in volume measurements are significant in analytical chemistry but all volumetric glassware have errors and obscurities linked with the measurements observed. Miniscule damage in a glassware due to aging, abuse and chemicals can create systematic errors in the observational measurements. Volumetric pipets and burets can be used for fairly accurate measurements if they’re standardized correctly. The purpose of this exercise is to measure volume and mass, to evaluate precision of the measurements, and to use the data to calculate the density or standard deviation. This experiment is achieved by first weighing the mass of a coin, mass of weighing paper and then measure both objects together to obtain the average mass of a coin. Following the introduction of calibrating with an analytical balance, we are given the volume of water to transfer into an Erlenmeyer flask or beaker by pipet/buret to obtain the actual volume delivered using the density of water at the given temperature. The process will be repeated three times for each given volume of water. Correspondingly, I will assess the error in the ability to read the glassware accurately by calculating a combined standard deviation of the total mass of the coin, the tolerance level for each volume delivered of water, and the density of water.
Experimental:
In order to evaluate the precision of an analytical balance or volumetric apparatus we must repeat each trial three times and then calculate the average. Obtain a coin (penny, nickel, or d...
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...s with the correct number of significant figures.
This first laboratory exercise has two primary goals. The first goal is to practice the classical techniques of weighing with balances and making volumetric measurements using glassware. For much of analytical chemistry, the accuracy of the entire analysis depends on the accuracy to which the standard (or standards) are compared. The second goal is to introduce and utilize certain concepts of statistical treatment of data. Carefully obtained results are useless unless their values and their limitations are known. The following statistical concepts are introduced in this laboratory exercise: accuracy and precision (absolute and relative); estimation of error (deviation); propagation of error; significant figures; Gaussian (normal) distribution; average (mean); median; standard deviation; and confidence interval.
the replicate shows the same trend as the first experiment. I used a measuring cylinder and a beaker to measure out the amounts of water; however these did not seem to affect the quality of my results. To increase the accuracy of my results I could have perhaps used a burette. Even though I did the best I could to keep the experiment accurate, I did. some places there were mistakes that unintentionally occurred.
The results of this experiment are shown in the compiled student data in Table 1 below.
I believe that a suitable procedure was followed that ensured that all inaccuracies in readings occurred due to human errors in reading. A syringe rather than measuring cylinders being used avoided errors in the measurements of volumes of solutions. This left no room for inaccuracies in not accounting for the meniscus as a syringe will leave no room for a meniscus and bears detailed volume readings, (to the nearest tenth of a cm3). This procedure yielded fewer inaccuracies meaning that results were more reliable.
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Planning Firstly here is a list of equipment I used. Boiling tubes Weighing scales Knife Paper towels 100% solution 0% solution (distilled water) measuring beakers potato chips Cork borer. We planned to start our experiment by doing some preliminary work. We planned to set up our experiment in the following way.
In this experiment, there were several objectives. First, this lab was designed to determine the difference, if any, between the densities of Coke and Diet Coke. It was designed to evaluate the accuracy and precision of several lab equipment measurements. This lab was also designed to be an introduction to the LabQuest Data and the Logger Pro data analysis database. Random, systematic, and gross errors are errors made during experiments that can have significant effects to the results. Random errors do not really have a specific cause, but still causes a few of the measurements to either be a little high or a little low. Systematic errors occur when there are limitations or mistakes on lab equipment or lab procedures. These kinds of errors cause measurements to be either be always high or always low. The last kind of error is gross errors. Gross errors occur when machines or equipment fail completely. However, gross errors usually occur due to a personal mistake. For this experiment, the number of significant figures is very important and depends on the equipment being used. When using the volumetric pipette and burette, the measurements are rounded to the hundredth place while in a graduated cylinder, it is rounded to the tenth place.
A random error is caused by any factor which randomly affects the amount of scatter in the data. An increase in sample size allows averages to be calculated which reduces the effects of these random errors. By removing outliers in the data, the effect of random errors can be further minimised. A large amount of scatter in results indicated low precision and a large number of random errors. Some possible random errors in this experiment may have arisen when measuring the 12mL of milk solution for each test tube; some may have had slightly more and others slightly less than 12mL. Another random error could have occurred when adding 4 drops of methylene blue, some drops may have contained more liquid than others, meaning some test tubes may have contained less methylene blue indicator than
Random and systematic errors are both factors that can affect the reliability and accuracy of the results respectively. As all the graphs contained outliers, and hence, scatter, this indicates that random errors were present. Such errors may result from the inconsistent masses of the Alka Seltzer tablets. As these tablets were cut manually with a knife, it is unlikely that the mass of each half of an Alka Seltzer tablet would be the same. Thus, when using the tablets to react with HCl, the true number of tablets reacting would have not been the same as the number denoted for the trial, and with each repeated trial for the same number of tablets reacting, the reacting mass and ratio would have not been inconsistent. Consequently, the
One possible source of experimental error could be not having a solid measurement of magnesium hydroxide nor citric acid. This is because we were told to measure out between 5.6g-5.8g for magnesium hydroxide and 14g-21g for citric acid. If accuracy measures how closely a measured value is to the accepted value and or true value, then accuracy may not have been an aspect that was achieved in this lab. Therefore, not having a solid precise measurement and accurate measurement was another source of experimental error.
Therefore, the glucose concentration of solution X could have been anything between 1% and 10% glucose concentration. By its color, it seemed to be closer to test tube 1; therefore, I estimated it to be 7%. However, this method is extremely inefficient, and that estimate could easily be wrong. Hence, this method is semi-quantitative and has several limitations. Too much is left down to estimation, where human error could easily occur because in-betweens cannot be accurately measured and have to be guessed at.
The density was measured by using an electronic densitometer. This apparatus operate by using the Archimedes Principle, which states the apparent loss in weight of a body immersed in fluid, is equal to the weight of the fluid displaced (Orr et a.l, 2003).
There is also the potential of human error within this experiment for example finding the meniscus is important to get an accurate amount using the graduated pipettes and burettes. There is a possibility that at one point in the experiment a chemical was measured inaccurately affecting the results. To resolve this, the experiment should have been repeated three times.
Possible sources of error in this experiment include the inaccuracy of measurements, as correct measurements are vital for the experiment.
A knot was tied about one inch from the end of the dialysis tubes. Then, three graduated cylinders were filled with twenty millimeters of either distilled water, 0.5 M sucrose, or 1.0 M sucrose. Using a funnel, each solute was poured into the corresponding dialysis tube. To keep the solute from leaking, another knot was tied about one inch of the opposite end. As the knot was tied, two fingers were used to remove air bubbles from the bag. Subsequently, each bag was rinsed with distilled water to assure that there was no sucrose residue, and then dried off with a paper towel. After waiting for a scale to display zero grams, each bag was then coiled on top of the scale to identify the mass in grams. The initial mass was recorded. Three containers were gathered and filled approximately two-thirds full with distilled water. Then, the three dialysis tubes were immersed into the corresponding container to soak in the distilled water for twenty minutes. To find the mass of the bags after being soaked in water, the bags were dried with a paper towel, and then coiled on top of the scale once again. The final mass was recorded. Finally, the mass difference and the percent change in mass was calculated and
Remove the extra solvent on a steam bath under a hood while flushing the flask with N2 gas, leaving the crude extract. Weigh extract.