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Chemistry Sean Skiver

Density of Solids and Liquids Nick Alexander, Mike Alexander

Due: 10/3/11 Lab: B day

Turned in: 10/4/11

I. PURPOSE

The purpose of this lab was to determine the density and volume of unknown liquids.

II. MATERIALS

Plastic tray (to hold metal), electric scale, 100 mL graduated cylinder, unknown liquid, metal sample.

Procedure

The first step in our lab, as in every other lab, was to dress in the proper lab apparel. After putting on our goggles and apron, my group was ready to calculate the density of a sample of metal.

Before calculated the density, my group and I had to acquire the mass of our metal. To do this, we used our metal scale, which calculated weight in grams. Before weighing the metal, we had to put our plastic trey on the scale and re-zero it, for the total mass could be thrown off by the little weight the trey holds. From there, we placed the metal on the scale. Making sure the metal was steady, and not shifting weight, we read the scale and recorded our results on our data table. Instead of only recording one result, our group was instructed to record three results, to ensure accuracy in our recordings. If measured correctly, all three recordings should be the same.

After finding the mass, we were ready to find the volume. To find the volume, we poured a little more than 50mL of water into a 100mL graduated cylinder. We recorded this value then we put the solid into the graduated cylinder, by tipping it to the side a bit and rolling the metal sample in, so it didn’t splash any water out. We recorded the new value in our data chart. We were now ready to calculate density. To calculate volume, we subtracted the original value from the metal-water mixture. From there, we calculated the density of the solid. To calculate density, we took the mass of the solid, and divided it by the volume of the solid. Again, we did this three times to ensure accuracy.

After finding the density of the a solid, we had to find the density of an unknown liquid. To do this, we used a graduated cylinder. We sat the graduated cylinder on the scale and re-zeroed it, as we did before to ensure the weight of the graduated cylinder is not added on to our final answer. With our scale re-zeroed, we poured 15mL of an unknown substance into the graduated cylinder to record its volume. We did this three times and recorded each trial in our data charts. While doing this we also recorded the mass of our liquid plus the mass of our graduated cylinder. We then calculated the density the same way we calculated the density of the solid.

Observations and Results.

See data in lab.

Error Discussion.

I feel that both our readings, and our final answers were very accurate. Although, Many errors, both human and technical, may have occurred. For example, when weighing the solid sample to find its mass, the pieces of the solid sample could have been moving around on the scale, shifting it’s weight. Thus making the weight inaccurate. If the weight was measured incorrectly, our mass would be measured incorrectly, thus making our answer off by a small, or large amount. Another error that could have occurred is a misinterpretation of the amount of liquid in our graduated cylinder. If I, or one of my classmates had not read the amount of liquid by the meniscus, our reading would not be to the correct tenths place. If this misreading would have been used, both our volume and density would not be correct. Also, if when placing the solid sample in the graduated cylinder, some of the water could have splashed out of the cylinder. Even a small, negligible amount would have come out, it could still jeopardize our chances of getting the most correct answer possible.

There could have been quite a few errors that could have occurred in measuring the volume of our unknown liquid. Due to the sticky, syrupy, consistency of the liquid, much of our sample could have stuck to the side of our graduated cylinder. If this happened, we would have measured less than what was actually in the graduated cylinder. Also, when measuring the amount of liquid in the graduated cylinder, one of my classmates, spilled our sample on the countertop of which we were working on. This left my classmate with nothing but memory of what the reading was, which could have been very inaccurate. All of our measurements could have been greatly affected by human error in reading the graduated cylinder, or the scale. If someone was not level with the graduated cylinder, and was reading it from an above point of view, then the readings would be completely off. Also, if the graduated cylinder had been tipped at an angle and read, the readings, again, would be completely off.

One of the main problems in gaining perfect precision of measurements, was rounding to the nearest tenths place. If our answers could have been to the hundredths, or thousandths place, our readings, and our answers would have been much more precise.

The most expected place for error was definitely in human error. Weather it be in math, or communication. While the measurements of our mass density or volume could have been correct, punching them into the calculator may have proven problematic, if someone pushed a wrong button or misread the readings. Also, if someone requested a reading from a group member, and misheard what he or she said, the readings could be affected greatly.

Conclusion

Based on the syrupy like texture of our unknown liquid, I would say it was corn syrup. Not only because of the texture, but also because it was cohesive with our results. Another reason I am positive that it was corn syrup, is because when my classmate spilt it on our lab station, It was very hard to clean up, without soap and water, just as corn syrup is to counter top.

It is possible that our unknown sample wasn’t any of the given answers, because it did not match exactly with any of the liquids.

Our measurements are different from the given measurements because instead of reading one definite answer, we recorded 3 similar answers. Also, the measurements could be inaccurate because if something was misread by just a tenths place, it would greatly affect the final answer.

To improve the accuracy of our results, we could have double checked our math results, and read the measurements of the liquids more carefully.

The density of the water is higher than the density of petroleum oil, thus making it float on the waters surface.

Using the accurate measurements of a known liquid to compare to an unknown liquid, we can make a close estimate to what the unknown liquid will be.

My Final Thoughts.

By using the materials available, my classmates and I made precise and accurate measurements to find the mass, density, and volume of a metal, and an unknown liquid. I would say my group met the requirements of the lab because not only were our reading precise, they were also accurate according to the actual mass, volume and density.