Chapter 1, Problem 21RPS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# You and your lab partner are asked to determine the density of an aluminum bar. The mass is known accurately (to four significant figures). You use a simple metric ruler to measure its dimensions and obtain the results for Method A. Your partner uses a precision micrometer and obtains the results for Method BThe accepted density of aluminum is 2.702 g/cm3. (a) Calculate the average density for each method. Should all the experimental results be included in your calculations? If not, justify any omissions. (b) Calculate the percent error for each method's average value. (c) Calculate the standard deviation for each set of data. (d) Which method's average value is more precise? Which method is more accurate?

(a)

Interpretation Introduction

Interpretation: The average density for each method and the justifications for omissions has to be given.

Concept introduction:

Precision: Is a measurement indicates how well several determination of the same quantity agree.

Accuracy: Is the agreement of a measurement with the accepted value of the quantity.

Percent error: The difference between measured result and the accepted value.

Percenterror=ErrorinmeasurementAcceptedvalue×100%

Error in measurement = Experimentally determined value - Accepted value.

Explanation

Average density Value for Method A and B:

AverageÂ densityÂ forÂ MethodÂ A:Â 2.2+Â 2.3+Â 2.7Â +Â 2.44Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â =Â 2.4Â g/cm3.AverageÂ densityÂ forÂ MethodÂ B:Â 2.703+Â 2.701Â +Â 2

(b)

Interpretation Introduction

Interpretation: The percent error for each method’s average value has to be calculated.

Concept introduction:

Precision: Is a measurement indicates how well several determination of the same quantity agree.

Accuracy: Is the agreement of a measurement with the accepted value of the quantity.

Percent error: The difference between measured result and the accepted value.

Percenterror=ErrorinmeasurementAcceptedvalue×100%

Error in measurement = Experimentally determined value - Accepted value.

(c)

Interpretation Introduction

Interpretation: The standard deviation for each set of data.

Concept introduction:

Precision: Is a measurement indicates how well several determination of the same quantity agree.

Accuracy: Is the agreement of a measurement with the accepted value of the quantity.

Percent error: The difference between measured result and the accepted value.

Percenterror=ErrorinmeasurementAcceptedvalue×100%

Error in measurement = Experimentally determined value - Accepted value.

(d)

Interpretation Introduction

Interpretation:

The method that has the more precise value and accurate has to be given.

Concept introduction:

Precision: Is a measurement indicates how well several determination of the same quantity agree.

Accuracy: Is the agreement of a measurement with the accepted value of the quantity.

Percent error: The difference between measured result and the accepted value.

Percenterror=ErrorinmeasurementAcceptedvalue×100%

Error in measurement = Experimentally determined value - Accepted value.

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