A 2.634 -g sample containing impure CuCl2 ·2 H2 O was heated. The sample mass after heating to d

step 1 Upon heating the copper chloride dihydrate, let's find the mass percent of copper chloride dihyd

A 2.634 -g sample containing impure CuCl2 ·2 H2 O was...

A 2.634 -g sample containing impure $\mathrm{CuCl}_{2} \cdot 2$ $\mathrm{H}_{2} \mathrm{O}$ was heated. The sample mass after heating to drive off the water was 2.125 g. What was the mass percent of $\mathrm{CuCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ in the original sample?

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Key Concepts

Stoichiometry of Dehydration Reactions

Stoichiometry in the context of dehydration reactions relates the mole ratios between the hydrated compound and its anhydrous form. By computing the molar masses of the compounds, one can determine how much anhydrous material corresponds to a given amount of the hydrate. This relationship is critical in converting mass measurements before and after heating.

Hydrates and Water of Crystallization

This concept involves understanding that certain compounds, known as hydrates, have water molecules incorporated into their crystalline structure in fixed stoichiometric ratios. When such a compound is heated, the water of crystallization is driven off, resulting in an anhydrous compound. Recognizing the difference between the hydrated and anhydrous forms is essential for calculating the original amount of the compound in a sample.

Mass Percent Purity Calculation

Calculating mass percent purity involves determining the fraction of the pure substance in a sample by comparing the mass of the substance after processing (such as heating to remove water) to the original mass. This calculation is performed typically by taking the mass of the pure component, dividing it by the original sample mass, and multiplying by 100 to obtain a percentage, which reflects the purity of the sample.

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