In experiment concerning potentiometric determination of puriy and Ka of KHP, we obtained an experimental pKa of 5.04 and when compared with the theoretical pKa of 5.51, we obtained a % relative error of 192%.
Could this error mean that a cerain impurity in the KHP sample effected this deviation?
I think an impurity could introduce an error in this determination.
To determine if a certain impurity in the KHP (potassium hydrogen phthalate) sample could have caused the observed deviation in the experimental pKa value, we need to analyze the % relative error. A % relative error of 192% indicates a significant deviation from the theoretical value.
Typically, the presence of impurities can affect the accuracy of experimental results. In this experiment, the purity and pKa of KHP were being determined potentiometrically. Potentiometric determination relies on measuring the potential difference between two electrodes – a reference electrode and an indicator electrode – to determine the concentration or extent of a reaction.
To investigate if a particular impurity led to the high % relative error, you can consider the following steps:
1. Check the purity of the KHP sample: Ensure that the KHP used in the experiment is of high purity. Impurities present in the KHP can affect the accurate determination of pKa.
2. Analyze the nature of the impurity: If you suspect that an impurity caused the deviation, identify the impurity or impurities present in the KHP sample. This can be accomplished through techniques such as spectroscopy (e.g., UV-Vis spectroscopy) or chromatography (e.g., HPLC, GC).
3. Investigate the properties of the impurity: Once you have identified the impurity, determine its properties such as its chemical structure, solubility, and potential reaction with the potassium hydrogen phthalate. This analysis will help in understanding how the impurity could alter the experimental pKa value.
4. Compare the known properties of the impurity with the observed deviation: Evaluate whether the identified impurity possesses properties that could impact the pKa determination. Consider factors such as potential reactions leading to pH changes or interactions with the indicator electrode.
5. Perform control experiments: If you suspect that the impurity causes the deviation, conduct control experiments using a pure KHP sample. Compare the results from the pure sample with those obtained from the impure sample. If the pKa values show a significant difference, it further supports the idea that impurities are responsible for the deviation.
Remember, the presence of impurities can lead to significant errors in experimental measurements. Therefore, it is crucial to evaluate the purity and potential impurities when examining the deviation in experimental results.