1.5.2: Comprehension Check

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Exercise \(\PageIndex{1}\)

A reported value of 45.35 g implies that the mass is between ___ and ___.

Answer: Mass is between 45.34 g and 45.36 g. It is 45.35 g plus or minus 0.01 g.

Is it possible for a number to have NO uncertainty?

Answer: A defined value or a number of counted items could be exact and therefore have no uncertainty.

Which of the following could be used to measure the precision of a set of numbers?

a) average (mean)

b) percent error

c) standard deviation

d) median

Answer: c) standard deviation (It tells how close a group of values are to each other. The other choices do not do that.)

Exercise \(\PageIndex{1}\)

You perform an experiment to determine the density of copper, and you obtain a value of 8.62 g/mL. Your reference lists the accepted value as 8.96 g/mL. What is the percent error of your measured value?

Answer

It is 3.8%.

The difference between the values, 0.34 g/mL, is divided by the accepted value of 8.96 g/mL. The result is 0.038. This is multiplied by 100% to give 3.8%.

Exercise \(\PageIndex{1}\)

You are measuring the liquid that is dispensed by a pump that is supposed to dispense 25.00 mL. You measure the following amounts: 24.72 mL, 24.88 mL, 24.85 mL and 24.77 mL. Calculate the average, standard deviation, and percent error.

Answer: Average = 24.81 mL. Standard deviation = 0.07 mL. Percent error = 0.76 %