Density: A Study in

Precision and Accuracy

(Part A & B)

Section: chem141 (6655)

Jan 29th, 2013

Purpose:

Part A: the major purpose of this experiment is to understand and to know the difference between the two separated concepts of precision and accuracy. Also, to learn the calculation of the standard deviation of measurements and to notice the importance of the random error and the systematic error.

Part B: the goal of this part is to know the aspects of statistical treatment of data which is validity and to consider the valid correlation between a change in a given variable and the result measured.

Theory:

One of primary concepts in any measurements is the precision, which refers to the random variations in the measurements. But it is very independent of accuracy, where a person can be very precise but inaccurate and vise versa. Precision is a way of measuring the random error, error that direction of effect is unknown. The experimental errors are considered random if the result of the measured values are either too high or too low.

In this experiment we will calculate the precision by calculating the standard deviations of the measurements. It is calculated by the following equation which is the same equation for calculating the random error:

Where x represent each individual measurement, while x is the average of the measurements. “n” is the symbol of the number of the measurements. After measuring the average and we plug in the values into the equation above. After that we calculate the result that the average and the standard deviation is combined to yield by this equation:

Where t is the standard deviation. The digit of the average and the standard deviation have to be the same.

While the accuracy, the closeness of the measured value to the standard value, is a measure of the systematic error which is a potential error that has a predicted effects of the results. The accuracy is measured by the percent...