Accuracy
Definition and meaning of Accuracy in chemistry.
Accuracy is a core measurement standard that scientists use in analytical chemistry. It describes how close a test result is to the actual true value of the sample. A highly accurate measurement must contain a very small amount of total error.
In more detail
In chemistry, accuracy evaluates the correctness of the entire testing process, including sample preparation and tool settings. It is different from precision, which only measures how closely repeated tests agree with each other. For example, a scale might yield the exact same wrong mass ten times in a row.
This measurement is highly precise but has very poor accuracy due to a systematic error. Systematic errors are steady, predictable flaws caused by uncalibrated instruments or contaminated chemical standards. To improve accuracy, chemists must identify and remove these steady biases from their lab procedures.
They also run blank tests containing only solvent to subtract background noise from their instruments. Additionally, scientists calculate percent error to mathematically express the accuracy of their final results. This calculation compares the experimental value directly to the accepted value.
They validate their methods by testing certified reference materials, which have a known, verified composition. A common student misconception is assuming that a precise test is always accurate. However, a repeatable experiment can still be incorrect if the equipment is not calibrated properly.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Definition concept | Closeness to true or accepted reference value |
| Primary obstacle | Systematic errors like miscalibration |
| Relationship to precision | Completely independent concepts |
| Validation methods | Testing certified reference materials |
| Standard metric | Percent error or absolute error |
A chemist tests a standard solution containing exactly 50.0 parts per million of calcium ions. The laboratory spectrometer reads 49.9, 50.1, and 50.0 parts per million across three separate trials. The average result is exactly 50.0, which proves that the test method has outstanding accuracy. Because the individual trials are also very close together, the experiment has high precision as well. This combination of correct averages and small variations gives scientists great confidence in their data.
Frequently asked questions
How do accuracy and precision differ in a lab?
Accuracy measures how close a test is to the truth, while precision measures repeatability.
What causes a chemistry test to lose its accuracy?
Systematic errors, such as a dirty sensor or an uncalibrated scale, skew the results.
Why do chemists use blank solutions?
Blank solutions help chemists measure background signal so they can subtract it from their data.