Final answer:
Residual water in a volumetric flask will lead to a lower concentration of the solute than intended because the final volume of the solution exceeds the specified volume of the flask. This will cause a decrease in the measured property of the solution that is directly related to its concentration, therefore affecting the accuracy of the analysis.
Step-by-step explanation:
When preparing a standard aqueous solution using a volumetric flask, the presence of residual water will cause a dilution effect. A standard solution aims to have a specific concentration by dissolving a precise mass of solute in a precise volume of solvent, typically distilled water, up to a calibration mark on the flask. If there is water left in the flask before this process begins, the final volume will be greater than intended once the solvent is added. This results in a lower than expected concentration of solute in the solution because the number of moles of solute remains the same while the volume of the solution is increased.
The measured property of the solution which is directly related to concentration, such as absorbance in spectrophotometry or electrical conductivity, will be lower than it should be for a given concentration. Therefore, the analysis based on this incorrect concentration will not be accurate, and the deviation in the expected results depends on the amount of residual water present. Using a volumetric flask is essential for accuracy in preparing solutions, and it must be free of residual liquids before use to ensure the correct concentration of solute is achieved.