Understanding Percent Error
In chemistry, percent error quantifies how closely an experimental measurement aligns with a known or accepted value. It provides a standardized way to express the discrepancy between a result obtained in the laboratory and the true value. This calculation helps evaluate the accuracy of experimental data, indicating the reliability of a measurement or an entire experimental procedure.
Scientists rely on percent error to assess the quality of their findings and identify potential issues within an experiment. Knowing the extent to which an experimental result deviates from a known standard allows for a critical review of the methods used and the instruments employed. By understanding this deviation, researchers can pinpoint areas for improvement, ensuring more dependable results in future investigations.
Calculating Percent Error
Calculating percent error involves a straightforward formula: Percent Error = |(Experimental Value – Accepted Value) / Accepted Value| × 100%. The absolute value ensures that the result is always a positive percentage, reflecting the magnitude of the difference.
To illustrate, consider an experiment where the density of a substance is measured. If the accepted density of a particular liquid is 1.00 g/mL (accepted value) and a student’s experiment yields a density of 0.98 g/mL (experimental value), the percent error can be calculated.
First, subtract the accepted value from the experimental value: 0.98 g/mL – 1.00 g/mL = -0.02 g/mL. Next, take the absolute value of this difference, which is 0.02 g/mL. Then, divide this by the accepted value: 0.02 g/mL / 1.00 g/mL = 0.02. Finally, multiply this result by 100% to express it as a percentage: 0.02 × 100% = 2.0%. This indicates a 2.0% error in the student’s measurement of the liquid’s density.
Interpreting Your Results
The calculated percent error provides insight into the accuracy of an experimental outcome. A lower percent error indicates that the experimental value is closer to the true or accepted value, signifying greater accuracy. Conversely, a higher percent error suggests a larger deviation, implying less accurate results.
A percent error of 0% means the experimental value exactly matches the accepted value. In many introductory chemistry settings, a percent error below 5% is often considered acceptable, though this can vary significantly depending on the complexity of the experiment and the precision of the equipment used.
Various factors can contribute to percent error in experiments. These include limitations of measurement devices, which possess inherent imprecision, or issues with instrument calibration. Human factors, such as misreading scales, incorrect calculations, or poor experimental technique, can also introduce deviations.
Accuracy Versus Precision
Accuracy and precision are distinct concepts, and percent error specifically addresses accuracy. Accuracy refers to how close a measured value is to the true or accepted value.
Precision describes how close multiple measurements are to each other, indicating the reproducibility of the results. Measurements can be precise without being accurate if they are consistently close to one another but far from the true value. For example, consistently getting the same incorrect reading for a known substance would demonstrate high precision but low accuracy.
Percent error is a direct measure of accuracy. It quantifies the deviation from a known standard. It helps determine if an experimental setup or method consistently yields results close to the established truth. While precision is about consistency, percent error focuses on the correctness of a single measurement or the average of several measurements compared to what is expected.