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Measurements: Accuracy and Precision

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1. Convert the length and height measurements for the packet that contains the aluminum shot from units of cm to units of mm using the unit-factor method. Cm is converted to mm using the equation mm= cm/0.10000. So, when you place the 5 or 6.5 cm measurement in the equation you get 5cm= 50 mm and 6.5cm = 65 mm. 2. Convert the temperature measurements for the faucet water and the ice water from oC to oF, using the following equation: oF = 1.8(oC) + 32. Using the above equation, 26◦ c = 78.8◦ f and 7◦ c= 44.6◦ f 3. Convert the volumes of the water in the 10-mL and 50-mL graduated cylinders from mL to L, using the unit-factor method.

Using the equation to covert ml to l which is L= mL/1000, we find that 7.1 mL = 0.0071000L and 7ml = 0.0070000L 4. Looking at your measurements for the volumes of water in the 10-mL and 50-mL graduated cylinders, are your values identical? Discuss at least two reasons why the measurements were not identical. The measurements were off by just a hair. Why? One of the reasons could be that I couldn’t successfully get all of the water from the 10ml cylinder to the 50ml cylinder. Some water was going to be retained in the cylinder or in the pipette. Part II (Questions 5-11 are worth 10 points each.)

5. Calculate the volume of the 50mL graduated cylinder using your measurements of diameter and height, using the formula V = ∏ r2h (r=½ diameter). This is your experimental value. Assuming the accepted value of the volume of the graduated cylinder is 50.00 mL, calculate the percent error of your volume calculation, using the following formula: Given the height, 7.2 cm, and the rate, 2.75 cm, the experimental volume of the cylinder is 171.06 ml. Percent Error = /accepted value – experimental value/x 100

accepted value
(50.00 ml – 171.06ml/ 50) X 100 = 242.12%

6. Calculate the mass of 10ml of water in the graduated cylinder using 1/5 the volume calculated in #5 above and the density of water of 1.00 g/mL. Calculate the mass of the water using the formula for density: Density = mass  volume

The volume is 171.06. Dividign it into 5 brings the mass to 34.21. 34.21/171.06 = .20. So therefore the density equals. 20 or 20%.

7. Using 10.0 g as the accepted value for the mass of the water, and the mass calculated using water’s density in #6 above as the experimental value, calculate the percent error of your mass calculation, using the same formula as in #5 above. (10 g -34.21 g / 10 g) X 100 = 242.1

8. Calculate the volume of aluminum shot added to the graduated cylinder, using the following formula: (Volume of water + Al) – initial volume of water = volume of Al shot Volume of the water is 10 ml. So (18)- 10 = 8 ml.

9. Calculate the experimental value for density of the aluminum shot based on its mass (given on the outside of the packet) as well as its volume calculated in #10 above, using the following formula: Density of Al = mass of Al shot/ volume of Al shot

Mass = 19.9, volume 8
Density = 2.4

10. If the accepted value for the density of aluminum is 2.70 g/mL, calculate the percent error of your density calculation, using the formula listed in #5 above. (2.70 – 2.4 / 2.70) X 100 = 11 % error

11. What were the potential sources of error in this experiment? Why is it necessary to know the error of one’s measurements? Suggest some ways of minimizing error, if you were to repeat the experiment. Being 100% sure that there is only 10ml of water in the cylinder when you start the experiment as well as using the proper utensils needed are a few ways to minimize errors. Part III

12. Provide your value for the either the weight of the Earth, the volume of the atlantic ocean, or the temperature of the sun (in scientific notation) along with the citation. Then, show both conversions you chose to complete for this value. Show all work for your conversions. (12 points) The weight of the earth, per google.com, is 5.972E24 Kg. This is written in scientific notation as 5.97 x 10 ^24 13.

Explain why the use of scientific notation in chemistry is very important. (10 points) It helps to minimize the amount of numbers that are drawn out so that people can work quicker as well as read the information more accurately. 14. Give an example of a time when you have used unit conversions in everyday life, and explain why that knowledge is useful. (12 points) As a CNA in a hospital, I would often have to take peoples weights as well as their temperature. IF the scale was not on the proper setting I would need to convert their weight in pounds to kilograms for charting. The same thing happened frequently with temperatures. I would take a patients temperature, and then realize it was in Celsius on the machine and need to convert it to Fahrenheit.

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