In the experimental setup for C and H estimation, the combustion gases are passed through U-tubes. T — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Anhydrous $CaCl_2$ (or magnesium perchlorate) is used to trap water vapor. It must be placed first because the highly hygroscopic concentrated $KOH$ used to trap $CO_2$ would absorb both gases if placed first, ruining the individual mass measurements.