Question

In your own words, what is the difference between "accuracy" and "precision"? Give an example (your own example, no scales or dart-boards). Put your answer in the space below (for this and all other questions). This experiment will have you place some water into various pieces of glassware, read how much water the glassware says should be in the container, and then compare this reading to the actual volume of water in the piece. Describe how you will determine this "actual" volume. A student collects the following data from analyzing a graduated cylinder. Use it to calculate to calculate what the actual quantity of water in the cylinder was for each trial. Mass of empty cylinder = 27.491 g Trial One. Indicated volume of water in cylinder = 7.0 mL. Mass of cylinder + water = 34.283 Trial Two. indicated volume of water in cylinder = 6.7 mL. Mass of cylinder + water = 34.109 Trial Three, Indicated volume of water in cylinder = 5.9 mL. Mass of cylinder + water = 33.548 Using the information from the previous question, calculate how much, on average, the graduated cylinder's indicated reading differed from the actual amount of liquid inside.

Answer 1

1) The “accuracy” of a measurement is the closeness of the measurement to the true or accepted value of the measurement. Suppose you perform an experiment to determine the value of the gas constant, R. The accepted value of R is 0.08206 L-atm/mol.K. Suppose you did the entire experiment and obtained the value of R as 0.08310 L-atm/mol.K while a friend of yours got the value as 0.08245 L-atm/mol.K. Since your friend’s value was more close to the accepted value of R, hence your friend’s measurement is said to be more accurate.

The “precision” of a measurement is the closeness of the individual values to each other. Precision has little to do with the true or accepted value of the measurement; it is simply how the individual measurements compare to each other. Suppose you are your friend are doing an experiment again which requires you to say, calculate the mass of a compound. Suppose you measured the mass thrice and the three replicate measurements are 6.1 g, 6.0 g and 6.3 g. Your friend measured the same compound and obtained three replicate measurements as 5.5 g, 6.5 g and 5.0 g. Obviously, the values your friend obtained are farther away from each other. However, your values are close and hence your measurements are precise.