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Why must a precipitate be filtered and dried before it is weighed?
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In gravimetric analysis, a precipitate must be filtered and dried (or ignited) to ensure an accurate quantitative measurement of the desired constituent.1
The process is necessary for the following reasons:
- Separation: Filtration is required to isolate the insoluble precipitate from the remaining solution, allowing it to be weighed independently.1
- Purity: Washing the precipitate during filtration removes soluble impurities that could otherwise lead to errors in the final weight.1
- Consistency: Drying or igniting the substance removes water and other volatile components. This ensures that the final mass corresponds exactly to the chemical formula of the compound being analyzed, which is essential for calculating the precise amount of the constituent present in the original sample.1
Because the accuracy of gravimetric analysis depends on the purity and known composition of the isolated substance, these steps are critical to minimizing experimental error.12