Name:__________________________Period:______Date:___ Ms



Name:________________________ Period:____ Date:___________

Lab Partners: ______________________________________________

Precision vs. Accuracy Lab Activity

Introduction:

In the lab it is important to have data that is both precise and accurate. The accuracy of data depends on how close a measurement comes to the actual or “true value.” The accuracy refers to being “correct.” The precision of the data depends on how close several measurements are to each other. The precision of the data refers to data being “reproducible.”

1. The words “correct and true value” refers to the ___________________ of the data.

2. The words “repeatable and reproducible” refer to the ________________ of the data.

Let’s think about it…

If a scientist collected data of 5 mL, 5mL, and 5mL when measuring the volume of a liquid, the scientist had reproducible data so they were precise. The average of the three trials would give a value of 5mL. If the true value of the volume was 5mL, then the scientist was also accurate.

If the scientist collected data of 6 mL, 5mL, and 10mL, the data was not precise because the data was not the same each time, and was not reproduced. The average of the three trials gives the value of 7 mL. If the actual volume is 5 mL then the data was not accurate since it did not match the true value.

Pre-Lab Questions:

1. Indicate whether each diagram below is accurate only, precise only, both accurate and precise, or neither accurate nor precise.

Diagram A is _________________________________

Diagram B is _________________________________

Diagram C is _________________________________

2. A measurement was taken three times. The correct measurement was 68.1 mL. Indicate whether the set of measurements is accurate, precise, both, or neither.

|Data Set |Accurate, Precise, Both or Neither? |

|a) 78.1 mL, 43.9 mL, 2 mL | |

|b) 68.1 mL, 68.2 mL, 68.0 mL | |

|c) 98.0 mL, 98.2 mL, 97.9 mL | |

|d) 72.0 mL, 60.3 mL, 68.1 mL | |

4. Calculate the percent error for each question below. Show your work!

a) A student measured a string and recorded its length as 1.25 m long. Ms. Roman said it was actually 2.12 m long. What was the student’s percent error?

b) Ms. Zagelbaum said the volume of a liquid was 500.0 mL. One of her students measured the volume of the liquid and found it to be 499.7 mL. What was the student’s percent error?

c) A standard mass of 250.0 g was placed on a quadruple beam balance. The balance indicated that it had a mass of 243.9 g. What is the balance’s percent error?

Procedure:

1. Obtain a sheet of paper (1 paper per lab group) and tear it into 6 equal pieces.

2. Roll the 6 pieces of paper into paper balls.

3. Stand 3 feet away from the bucket.

4. Try to throw all six paper balls into the bucket.

5. Mark in the diagram below (labeled “Cup”) by placing an “x” where YOUR 6 paper ball landed in relationship to the bucket.

6. Pick up the six paper wads and hand them to a lab partner.

7. Repeat the above steps until each person has had a turn to collect their own data

8. CLEAN UP – The cup should have six paper balls in it when your group is done!

Discussion: Looking at the majority of your shots, comment on your accuracy and precision. Explain why your data was or was not accurate, and why your data was or was note precise. Use complete sentences and given an explanation for your reasoning.

Accuracy: _________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

Precision: _________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

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A B C

Cup

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