The volume of water in a volumetric flask is known to be 100.00± 0.05 mL at 25 degreeC and 1 atmosphere. A student uses a 100 mL measuring cylinder to measure the volume of water in the flask four times. The student’s results are shown in the table below. How would you describe the precision and accuracy of the student’s recorded volumes of water?
Trial
1
2
3
4
Volume (mL)
99.84
99.92
99.91
99.98
The results are accurate but not precise
The results are precise but not accurate
The results are not precise and accurate
There is not enough information to describe the precision and accuracy of the results
The results are precise but not accurate.
To evaluate the precision and accuracy of the student's recorded volumes of water, we can compare the measured values to the known volume of 100.00±0.05 mL.
Precision refers to the consistency or reproducibility of the measurements. It is indicated by the range or spread of the measured values.
Accuracy refers to how close the measured values are to the true or target value. It is indicated by the average or mean of the measured values.
Looking at the data, we can calculate the mean and range for the measured volumes:
Mean = (99.84 + 99.92 + 99.91 + 99.98) / 4 = 99.9375 mL
Range = Max Volume - Min Volume = 99.98 mL - 99.84 mL = 0.14 mL
Now, let's compare the results to the known volume:
The mean of the measured volumes (99.9375 mL) is very close to the known volume of 100.00 mL. This indicates that the results are accurate.
However, the range of the measured volumes (0.14 mL) is relatively large compared to the known uncertainty of ±0.05 mL. This indicates that the results are not precise.
Therefore, we can conclude that the results are accurate but not precise.