The goal of this lab is to introduce the concept of experimental error. A large

Question

The goal of this lab is to introduce the concept of experimental error. A large part of science involve evaluating experimental results. How does one know when a result is"good" and when it is "bad?" Knowing something about the error associated with an experimental measurement and the propagation of that error throughout the experiment can help in making an informed decision about the validity of a reported result. This is typically done through evaluation of accuracy and precision. Accuracy is the degree of agreement between the measured value and the true value. Often times, absolute true value is not known. A more realistic definition of accuracy would be the agreement between the measured value and the accepted true value. This is represented as percent error: percent error = literature value-experimental value percent error = literature value Precision is defined as the degree of agreement between replicate measurements of quantity. It describes the reproduciblity of a result, and is represented through error reporting: the same 10.0 ± 0.1 Measured value Error in measured value In this course, we will use uncertainty (if one measurement), standard deviation (if more than one measurement), or propagated error (if a value is calculated from measurements) to represent precision The smaller the error, the more precise the measurement Question 1 1 pts A 25.0-g sample of sodium chloride is massed on a balance. The masses are recorded as 24.9-g. 25.1- s. 25.1-g. and 25.0-g. What conclusion can you draw regarding measurements obtained from this balance?

Explanation / Answer

Question no. 1: The exact mass of the sample of NaCl is 25.0 g. From three trials, you are getting the value 24.9 g , 25.0 g and 25.1 g.

The average value of the three runs is: (24.9 + 25.0+ 25.1) g / 3 = 25.0 g

The value is accurate to the actual value and the three runs give values which are pretty close to each other (precise)

Answer is : Accurate and Precise.

Question no. 2:

Pecent error = (0.9999749-0.998)*100/ 0.9999749 % = -0.197%

Questiin no. 3:

Density = Mass/ Volume

For A: Average mass = (4.56 + 4.85 + 4.99) g / 3 = 4.6 g

Density of water = 4.8 g/ 5 mL = 0.96 g/ mL

Percent error = (1-0.96)*100/ 1 % = 4%

For B: Average mass = (10.25+10.48+9.95) g/ 3 = 10.23 g

Density of water = 10.23 g/ 10 mL. = 1.023 g/ mL

Percent error = (1-1.023)*100/ 1= -2.3%

For C : Average mass = (15.99+14.85+14.65) g/ 3 = 15.16 g

Density of water = 15.16 g/ 15 mL. = 1.01 g/ mL

Percent error = (1-1.01)*100/ 1= -1.0%

For D: Average mass = (19.66+19.98+21.12) g/ 3 = 20.35 g

Density of water = 20.35 g/ 20 mL. = 1.018 g/ mL

Percent error = (1-1.018)*100/ 1= -1.8%

Percent error is least for experiment C.So, the data of C gives highest accuracy

Question no. 4:

Most precise is : Method A

Question no. 5:

2.65 mL

Question 5:

24 mL.

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