Laboratory Techniques and Measurements
Abstract:There were several objectives in this experiment that allowed student to familiarize themselves with different techniques used a laboratory environment. Students were instructed to conduct measurements such as length, mass, temperature, volume, and density using common tools. Dilutions were also created during this experiment, and then calculated using basic algebraic formulae. This experiment allowed students to become proficient in using utensils in the lab, and in conducting basic measurements. Experiment and Observations: Length Measurements
In this experiment, students were required to measure three objects with a ruler showing and record the data in the table below, approximating to one decimal place. Object Measured Length in cm Length in mm Baby’s bottle 14. 2 cm 142 mm Pen 14. 5 cm 145 mm Diameter of the opening of a glass 8. 4 cm 84 mm Temperature Measurements There were two temperature measurements: warm and cold. Students were instructed to measure the temperature of hot water in three stages: hot from the sink, the temperature at the boiling point, and finally, the temperature after boiling the water for 5 minutes.
Afterwards, students were directed to measure the temperature of cold water in three stages: cold water from the tap, temperature of water after adding ice cubes, and finally the temperature of the same water after 5 minutes. Students were required to add the data in the table below. The measurements were done in Celsius. Hot water from tap (C0) Boiling water (C0) Boiling water after 5 minutes (C0) 54 C0 93 C0 95 C0 Cold water from tap (C0) Ice water (C0) Ice water after 5 minutes (C0) 22 C0 18 C0 5 C0
Volume Measurement In this experiment students were instructed to measure the volume of the water after filling a test tube, and then pouring the content into a 25mL graduated cylinder. The volume was to be recorded in the table below. In the next step, students were required to measure the volume of a thin-stemmed pipet, by filling it with water, then adding this water into the graduated cylinder one drop at a time, until the 1mL mark was reached. The number of drops used were added to the table below.
Finally, students had to empty the content of the pipet into the graduated cylinder, and they were instructed to write the volume of the water from the graduated cylinder into the same table. The measurements were recorded in mL. Volume of test tube (mL) Number of drops in 1 mL Volume of pipet (mL) 12 mL 25 drops 5 mL Mass Measurement For this experiment, a digital scale was used. Students were instructed to use the correct tare in order to reduce inaccuracies. Students were required to try to guess the masses of these objects, and add their estimates into the table below.
Afterwards, they were instructed to weigh the objects, and record their actual masses into the same table. Measurements were recorded in grams. Object Estimated Mass of Object (g) Actual Mass of Object (g) Vitamin pill 0. 5 g 0. 6 g Empty plastic measuring cup 5 g 25. 8 g Container filled with garlic powder 200 g 271. 8 g Container filled with toothpicks 153 g 51 g Plastic container, filled ? of the way with parsley 25 g 24. 2g The lid of the scale used in this experiment 10 g 10. 1 g Wedding ring 5 g 3. 1 g Density Measurements In this section, several methods were used to measure densities.
1. Calculating densities using a scale, a graduated cylinder, and the formula: density = mass/volume – In the first step, students were required to determine the density of water, using a graduated cylinder, a small scale, and the density formula: density=mass/volume. These measurements were recorded in the table below. – In the next step, students measured the density of isopropyl alcohol through a similar method they measured the density of water. – In the following step, students were required to measure the density of salt solution through similar methods.
After measuring the mass of 5 mL of the salt solution, they were required to form a hypothesis on whether the density of this solution is higher or lower than that of water. The actual measurements were recorded in the table below. Hypothesis: the density of the salt solution would be greater than the density of water, because the mass of the salt solution is greater than that of the water, and when two fractions have the same number in the denominator (5), but the numerators are different, the fraction with the higher numerator will be the greater of the two. Mass A Mass B Mass A-B Object Graduated cylinder + substance
Graduated cylinder Substance Density (M/V) Water 21. 8 g 17. 2 g 4. 6 g 0. 9 g/mL Isopropyl alcohol 21. 5 g 17. 2 g 4. 3 g 0. 9 g/mL Saturated salt solution 22. 6 g 17. 2 g 5. 4 g 1. 1 g/mL In the next step, students were required to compare two different techniques of measuring density. 2. Water-displacement method In this experiment, students had to calculate the density of a metal bolt and a magnet using the water-displacement method. The data gathered was entered in the table below. 3. Archimedes’ method In this experiment, students were instructed to calculate the density of the same metal bolt and magnet via Archimedes’ method.
4. Math calculations method Once the comparisons between the above mentioned techniques were completed, students were required to use the math calculations method to determine the density of the magnet. Since the magnet has measurable sides, this is a viable technique. A B B-A Object Graduated cylinder volume Graduated cylinder + object Object volume (mL) Object mass (g) Density (M/V) Metal bolt: water-displacement method 12. 5 mL 13. 5 mL 1. 0 mL 8. 0 g 8. 0 g/mL Metal-bolt: Archimedes’ method 1. 0 mL 8. 0 g 8. 0 g/mL Magnet: water-displacement method 12. 5 mL 13. 5 mL 1. 0 mL 4. 3 g 4. 3 g/mL
Magnet: Archimedes’ method 1. 0 mL 4. 3 g 4. 3 g/mL Magnet: math calculation method 0. 8 mL 4. 0 g 5. 0 g/mL Making a Dilute Solution While these steps didn’t require students to collect data into a table, they were instructed to perform certain tasks in order for them to learn how to use certain laboratory tools in order to prepare accurate dilute solutions. The instruments required for this exercise were a 0. 2 mL serological pipet with bulb and a 100 mL beaker. The students squeezed the bulb and placed the tip of the pipet into the beaker. When they released the bulb, they collected enough liquid to reach the 0 mark.
Students then released 1. 0 mL liquid from the pipet, then an additional 0. 5, and finally the entire 2. 0 mL liquid. In the following portion of the lab, students were required to observe a volumetric flask, which only measured 25mL volume (quantum sufficit) indicated by a line. Using the serological pipet, students delivered 5 mL of colored liquid into the volumetric flask. The rest of the flask was filled with water up to the 25 mL mark. I used prune juice, which has a reddish-brown color. When I added the water to it, the liquid became lighter reddish-brown color. Still, the mixture wasn’t uniform.
Most of the juice collected to the bottom of the flask, and the color gradually faded up to the 25 mL line. Calculations and Error When calculating the length of an object, errors in measurements were minimal, because the ruler was marked to millimeters. This ensured the margin of error was reduced. Had students used a ruler with only inches marked, the error would have been greater. Measuring the temperature was straight forward. I just had to ensure I kept the thermometer straight. The water boiled at less than 100 C0, and didn’t reach that temperature even after 5 minutes. The cold water did not reach the 0 C0, even with the ice in it.
These measurements were taken with a mercury thermometer, which are considered accurate. More accuracy could have been achieved by measuring the temperature with multiple thermometers. Measuring the volume in the graduated cylinder was also fairly accurate, because it was clearly marked. The design of test tube allowed me to fill it up completely. The chances of errors was slightly higher in this part of the experiment, due to the difficulty in adding an exact amount of fluid into the cylinder. 1-2 extra drops could make a difference. I attempted to measure by adding the liquids to where they were in one plane with the 5 mL mark.
The degree of error when measuring the number of drops in 1 mL was larger due to the possibility of the drops having different sizes. Smaller drops would have been needed to fill the cylinder to the 1mL line than smaller drops. The margin of error when measuring mass was decreased significantly by adjusting the tare appropriately, and using the same scale for every measurement. As shown in the table, most of the time, the actual measurement differed quite a bit from the hypothesized mass. For the measurement of density the following formula was used: density=mass/volume Density of water: 4.
6g/5mL = 0. 9 g/mL Density of isopropyl alcohol: 4. 3g/5mL = 0. 9 g/mL Density of salt solution: 5. 4g/5mL = 1. 1 g/mL Measuring the density of liquids yielded some errors. If rounded to two decimal places, water had a density of 0. 92 g/mL, and isopropyl alcohol had a density of 0. 86. This would have been more accurate, than the data actually entered into the table. Based on rounding requirements stating that the decimal places of the product should match the lowest decimal place of the numerator and denominator, I had to round to only one decimal place.
If rounded to one decimal place, water and isopropyl alcohol would show the same density, but the density of isopropyl alcohol is slightly lower than that of water. Measuring the density of objects yielded the same result in water-displacement test and the Archimedes’ method. Both had their own challenges. When using the water displacement method, students had to ensure that the water level was read accurately. With Archimedes’ method, students had to ensure the scale was appropriately calibrated, and they had to ensure the objects weren’t touching the side of the beaker.
Based on the data gathered, both yielded similar results. Water displacement method calculation for both the bolt and the magnet used was similar. The volume of water in the graded cylinder was 12. 5 mL in both instances. When dropping the bolt into the cylinder, the volume read 13. 5 mL. The same volume was recorded when the magnet was dropped into the cylinder. In order to determine the water displacement, the students had to subtract the volume of the water from the volume of the water when the object was in it. For the both objects, 13. 5g-12. 5 g=1. 0g. The weight of the bolt was 8. 0g, and the weight of the magnet was 4.
3 g. As such, the data recorded for the bolt was: density = 8. 0 g/1. 0 mL = 8. 0 g/mL, and density of the magnet was: 4. 3 g/1. 0 mL = 4. 3 g. For the Archimedes’ method, I used the scale. This method was easier, but the possibility of errors was greater, because I had to have a steady hand. I filled a beaker with water to the 50mL line, and placed it on the scale, then ensured the tare was set to 0. 0g. Slowly, I submerged the objects using a string, and the weight measured on the scale showed the density. I gathered the same results as in the water displacement test: density of the bolt: 8.
0 g/mL, and the density of the magnet was 4. 3 g/mL. Using the mathematical method yielded a different result. The volume had to be calculated using the measurements of the three sides. The value had to be converted into mL, and the mass had to be divided by the volume. Mass of magnet: 4. 3 g, volume of magnet = 5mm x 6mm x 25mm = 750 mm3 = 0. 750 mL. Density = 4. 3g/0. 750 mL = 5. 7 g/mL. Discussion and Conclusion The measurement for the length was straight-forward. There wasn’t too much of a margin for error. All the objects I measured were the exact length I added into the table.
I didn’t measure any objects that ended between the millimeter marks. One might argue that the baby’s bottle would be more difficult to measure, and measuring this object would yield the most errors, because of the shape of the object. Using a pen to connect the top of the bottle to the ruler alleviated much of this error, and allowed me to have an accurate reading for the length. Due to the design of test tubes, I was able to fill it all the way with the water, and this yielded accurate results when measuring its volume in the graded cylinder. Filling the pipet was a bit of a task until I found the right trick to it.
Counting the drops seemed somewhat subjective, because it depended on how big the drops were. The instructions did not state how bid the drops should be. One way to alleviate this error would be to describe the size of drops. Or, an even better way would be to use a pipet that is less flexible, and has standard drops flowing from it. As mentioned in the “Errors and Calculations” section, measuring temperature with an alcohol thermometer was fairly accurate. The degree of accuracy could have been known if the temperatures had been taken with multiple thermometers.
I expected the water to boil at less than 100 C0, because the house was above sea level, closer to Denver, CO. I did expect the water to reach that temperature after 5 minutes, but it didn’t. It seemed to cap out at 96 C0. My expectations were similar to the outcome when measuring the temperature of the cold water. I did not expect it to reach 0 C0, because there was plenty of liquid water in addition to the ice, even after 5 minutes. It was interesting to note the difference between the hypothesized mass, and the actual mass measured with the scale.
In some cases, I was only a tad off, while in other cases, I was very off. The degree of accuracy was questionable. It was based on the fact that I faith that the scale was calibrated properly. I did adjust the tare accordingly, but in order to ensure a better degree of accuracy, I could have weighed each object on multiple scales. I already knew the density of water, and as a result, I was happy to see that my measurements were accurate. Still, when measuring the isopropyl alcohol, if rounding to only one decimal place, the density was the same as that of water. Of course, when rounding to two
decimal places, the rubbing alcohol was slightly less dense than water, at 0. 86 g/mL versus 0. 92 g/mL. Rounding to more than one decimal place increased the accuracy. I expected the density of the salt solution to be higher, because the mass of the solution would increase compared to just water. Just as I had predicted, the density of the salt solution was 1. 1 g/mL. Measuring the densities with the water displacement vs the Archimedes’ method was surprisingly similar. I expected to see at least a slight difference, but both yielded the same results. The density of the bolt was 8.
0 g/mL, and the density of the magnet was 4. 3 g/mL. I could see based on these results why Archimedes’ method was accurate. Both methods required much precision. I had to ensure the scale was calibrated properly, and that my hands weren’t moving frantically while lowering the objects into the beaker. Based on these results, both measurements proved to be accurate. The mathematical method yielded some issues. The result was very different from the above methods. I even converted mm3 to mL to ensure accuracy. Still, the result was surprisingly different. The density was 5. 0 g/mL.
I added details on how I completed the calculations in the “Calculations and Errors” section. I was trying to devise different theories behind the discrepancies. I was thinking that it may have been that the length measurements had nothing to do with the actual material. We had to calculate the volume based on the length, height and width. This yielded 750 mm3, which is 0. 75 mL. The object’s density then would be 4. 3 g/0. 75 mL=5. 7 g/mL . Although the results were identical when measuring with the water displacement method and Archimedes’ method, these two methods are not always accurate.
The cylinder might be calibrated differently, water might spill when the object is drooped in it. Archimedes’ method can also be inaccurate. If the water or the hand moves, the numbers start changing on the scale. The mathematical calculation method is considered to be the most accurate, if the object has definite sides. Creating the mixture was fun, but based on the fact that the pipet can have hair bubbles trapped, I had to be very careful. One air bubble could throw off the entire experiment. Because I used prune juice, it all tended to gather on the bottom of the flask.
I was still able to see the juice disperse in the water, and the closer to the 25 mL mark, the lighter the color of the liquid. I didn’t think that the consistency of the juice was different, so I expected for the juice to evenly mix in the water. I was proven wrong by the experiment. Questions A. The water did boil at a lower temperature, because the experiment was conducted above sea level. The reason for this is that there is less atmospheric pressure at higher altitudes. Less pressure requires energy. B. The percent error is calculated with the following equation: 100 x(|experimental value-theoretical value|/theoretical value) |102-100|
100 x —————– = 100 x 0. 02 = 2% For water boiling at 1020C 100 |99. 2-100| 100 x —————– = 100 x 0. 08 = 8% For water boiling at 99. 20 100 C. First, we calculate the volume: 3. 6 cm x 4. 21 cm x 1. 17 cm = 17. 7 cm3 If we want the density in g/mL, we convert 17. 7 cm3 to mL, which is 17. 7 mL. Second, we determine the mass of the object, which is 21. 3 g. The density is found by dividing the mass by the volume. D=mass/volume D=21. 3 g/17. 7 mL = 1. 2 g/mL D. Density=mass/volume as a result Volume=mass/density The Au sample has a mass of 26. 15 g The density of the sample is 19.
30 g/mL Volume = 26. 15 g / 19. 30 g/mL Volume = 1. 35 mL E. This is a difficult question to answer, because based on my experiment, both methods were equally accurate. It depends on the object that is being experimented upon on, the tools used within the experiment, and the person completing the experiment. For example, for the bolt it would be easier to just use Archimedes’ method, because it is easy to just get a string, tie it on the bolt, and submerge it into the water. With the magnet it may be more beneficial to use the water displacement method, because the string might fall off.
If one doesn’t have steady hands, it is more beneficial for them to use the water displacement method. I believe it is a matter of preference and also a matter of what resources one has available. F. If one dropped the object into the beaker the measurements would be incorrect. The experiment specifically states not to touch the bottom or the sides of the beaker. It is important to complete the experiment gently. G. Although I got similar results when using Archimedes’ method as when I used the water displacement technique, there is more room for error when using Archimedes’ method.
The hands need to be perfectly still, without the water touching the beaker. Plus, the experimenter has to ensure the scale is calibrated properly. H. In this exercise, we can determine the density, because we have the volume and the mass. Volume = 0. 40 cm3 = 0. 40 mL Mass= 6. 0 g Density = mass/volume Density = 6. 0 g/0. 40 mL = 15 g/mL The density of gold is 19. 3 g/mL. As a result, this object is not made of gold. I. First, we convert 0. 25M to moles/L 0. 25M=0. 25 moles/L In order to determine how many moles of HCl we need, we have to multiply the 10mL by . 25mol/1000L. 10*(0.
25mol/1000L)=0. 0025mol In order to determine how much 1M HCl solution one should use, we have to multiply the 0. 0025 mol by 1000mL/1. 0 mol HCl 0. 0025 mol *(1000mL/1. 0 mol HCl) = 2. 5 mL Since we have 10 mL of solution, and 2. 5 mL of HCl, the amount of water used is 10 mL-2. 5 mL = 7. 5 mL. J. Using molarity to express concentration: Original liquid: 2. 43 M Volume of solution = 25. 0 mL = 0. 025L 2. 43 M = 2. 43 moles/L Molarity = moles of solute/volume of solution Molarity = (2. 43 moles/L)/0. 025L Molarity = 97. 2 M K. The color after diluting is lighter, because it is less concentrated.
The reason for the dilution is to make the original liquid less concentrated. The more the liquid is diluted, the lighter in color it gets. M. When diluting a liquid, the color gets lighter, the more water we add. The reason for this is the fact that the original liquid becomes less concentrated. The more water add, the more the original liquid disburses throughout the water. N. The water will boil faster in Colorado. The reason behind it is the difference in atmospheric pressure between seal level and high altitudes. The lower the pressure, the less energy is required to boil the water.
Based on the experiment, the water started boiling at around 920 C, and it didn’t reach 1000C even after 5 minutes. O. 1. Calculating the change: 4. 521g/(13. 534 g/cm3-13. 472 g/cm3) = 72. 919 cm3 (72. 919 cm3)/(? 0. 0252 cm2)=(72. 919cm3)/(3. 141×0. 000625cm2)=3. 714×105 mm. 2. Calculating the number of atoms of Hg in the thermometer: (4. 521 g)/(200. 592 g/mol)x(6. 022×1023 atoms/mol) g and mol cancel out Answer: number of Hg atoms: 1. 357 x 1022 P. 1. V=? r2h Vgold=? (4. 1cm2)(21cm) vgold=1109. 014 cm3 Densitygold =massgold/volumegold Massgold = densitygold x volumegold Massgold = (19.
3 g/cm3)(1109. 014 cm3) Massgold= 21403. 97 g Massgold = 21404 g Vsand = ? (4. 1 cm2)(21 cm) Vsand = 1109. 014 cm3 Densitysand = masssand X volumesand Masssand= densitysand x volumesand Masssand = (3. 0 g/cm3)(1109. 014 cm3) Masssand = 3327. 04 g Masssand = 3327 g 2. The alarm would have been tripped, because the sand is less massive than the gold. Although the volume is identical for both, the density isn’t. Because the density isn’t identical, neither is the mass. In our scenario, the mass wasn’t even comparable. The sand is much less massive than gold. Indiana Jones would have been in big trouble.