Controls are standard benchmarks in experiments, ensuring results stem from the tested factor, not external influences. They are fundamental for valid comparisons and drawing meaningful conclusions from chemical observations. Controls help establish the reliability and accuracy of scientific findings by providing a point of comparison, allowing researchers to isolate the effects of a specific variable.
The Purpose of Controls
Controls ensure experimental results are valid by isolating variables. They allow researchers to determine if observed changes are caused by the tested variable, rather than other factors. By providing a baseline, controls increase confidence in findings and help rule out false positives, ensuring any positive outcome is truly due to the experimental condition and not due to external factors or errors in the procedure.
Controls also identify potential errors in the experimental setup or procedure. If a control does not yield the expected result, it indicates a problem, such as contaminated reagents or faulty equipment. This confirms the experimental method is testing what it intends and provides a basis for comparison against the experimental group.
Different Types of Controls
Positive Controls
Positive controls demonstrate what a positive result looks like, ensuring the testing procedure can produce results when the expected outcome is present. For example, in an experiment testing for vitamin C, a known vitamin C solution serves as a positive control, expected to react with the testing reagent. If this control does not show a positive result, it suggests an issue with the reagents or experimental setup.
Negative Controls
Negative controls show what a negative result looks like, ensuring no change is observed when not expected. They confirm any positive result is genuinely due to the test condition, not external factors or contamination. For instance, distilled water serves as a negative control when testing for vitamin C, as it contains no vitamin C and should not react with the testing reagent. Any reaction in the negative control indicates contamination or an error.
Blank Controls
Blank controls account for reagents or background interference. They contain all experimental setup components except the analyte being measured. For example, when using a spectrophotometer to measure the concentration of a colored solution, a blank containing only the solvent and reagents is used to zero the instrument. This subtracts any absorbance caused by the reagents or solvent, providing a more accurate measurement.
Applying Controls in Experiments
Implementing controls in a chemical experiment involves careful planning. The control setup should be as identical as possible to the experimental setup, with the sole exception of the variable being tested. This consistency allows for direct and reliable comparisons between the control and experimental groups. For instance, if testing a new catalyst, the control reaction would proceed without the catalyst but under otherwise identical conditions.
Controls are run concurrently with experimental trials, not as separate, later tests. This simultaneous execution accounts for environmental changes or fluctuations in experimental conditions. Including controls as an integral part of the initial experimental design, rather than an afterthought, is essential for generating trustworthy and interpretable results. This practice ensures observed effects can be confidently attributed to the specific experimental manipulation.