Sarah Combs
Environmental Chemistry I
Lab Report 1
Accuracy and Measurements
Introduction: In this experiment we determined the difference in accuracy of two different sized cylinders. Accuracy is a measure of how close something is to its true value. To determine the accuracy we had to measure the volume and compare it to the theoretical volume, finding the relative error. Following this we used the density of water, 0.99720 g/mL, along with the mass we determined with a scale, to determine the volume of water in a 10 mL pipet using the formula D=mv.
Objective: The purpose of this lab is to determine which cylinder, the 10mL or 100mL is will produce a more accurate measurement. It was also looking to determine the accuracy of measurement
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The 10 mL cylinder was more accurate than the 100 mL cylinder. Our measured value in the 10 mL cylinder was closer to the true value than the measured value from the 100 mL cylinder. When using the smaller cylinder we had a relative error below 1% while when we used the larger one, our relative error was 2.4%.
2. While determining the average volume of a 10 mL pipet, it was easy to conclude that there are often errors when measuring due to our 1.28% relative error. There could have been many causes of this error but the most likely would be human error. Error leads to inaccurate measurements. Measurements are not always accurate but when there are more graduations and you can estimate with an extra significant figure, they are more accurate. To minimize error associated in measurements you can check to make sure the scale or balance is calibrated properly and also conduct several trials.
3. Significant figures are important in scientific measurement because they allow for a more accurate measurement, the more significant figures the closer the answer is to its true value even with the degree of uncertainty. It is important to know the degree of uncertainty in the measurements you are working with. In the smaller cylinder there were more graduations on the cylinder leading to a more accurate answer to begin with and the last significant figure is an estimation. There are more significant figures in the 10 mL cylinder than in the larger one due to more graduations on the cylinder to begin with.
Furthermore, using a graduated cylinder with markings below the 100 mL line would have allowed for more accurate measurements of the initial volume of air in the graduated cylinder.
When the liquid level is above the calibration line on the pipette, remove the bulb quickly and put your thumb or index finger over the pipette. Carefully “roll” finger to the side and allow the liquid to drop until the meniscus is level with the mark. Then hold the pipette over the flask to receive the liquid and remove the finger. Allow the liquid to drain out.
this is the best volume to use as it is about ¾ of a test tube full,
This means that there are more collisions between the solid and liquid. Amount of tap water H2O used, i.e. volume (in ml) of the syringe. Amount of Alka-Seltzer tablets used, i.e. quantity of the tablets. one is used for the. Number of times the solution is stirred.
Discussion: The percent of errors is 59.62%. Several errors could have happened during the experiment. Weak techniques may occur.
and C, also that there is a 4cm difference between A and C. Test tube
3. Add on of the following volumes of distilled water to the test tube, as assigned by your teacher: 10.0mL, 15.0mL, 20.0mL, 25.0mL, 30.0mL. (If you use a graduated cylinder, remember to read the volume from the bottom of the water meniscus. You can make more a more accurate volume measurement using either a pipette or a burette.)
The molar volume of the H2 in our experiment is very close to the theoretical molar volume, but I think that the deviation lies in the temperature of the H2O: in the first trial it is too high and in the second one too low.
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.
Some possible sources of error are how much water was put in the rocket, damaged measuring instruments, and inaccurate distances from the launching pad. The procedure of the lab instructed to put in 250 ML of water into the rocket but that may not have always been the case. Some people could have been holding the beaker which we measured the water in and that can make the water splash around. This would make it hard to get an exact measurement. It is possible people put in more water than instructed to add more fuel. Measuring the water precisely was not a strictly enforced rule and mishappens can happen. This would cause for an unfair advantage or disadvantage to whom did not put the equal amount of water as everybody else for their rocket
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.
- Each teaspoon may not have been equal. Measurements were made based on judgment and not exact measurements.
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.
from 10cm to 50cm to make it easier to see the difference in a graph.