Washing soda, a compound used to prepare hard water for washing laundry, is a
hydrate, which means that a
certain number of water molecules are included in the solid structure. Its
formula can be written as \(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot x
\mathrm{H}_{2} \mathrm{O}\), where \(x\) is the number of moles of
\(\mathrm{H}_{2} \mathrm{O}\)
per mole of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\). When a \(2.558-\mathrm{g}\)
sample of washing soda is heated at \(25^{\circ} \mathrm{C}\), all the water of
hydration is lost, leaving \(0.948 \mathrm{~g}\) of \(\mathrm{Na}_{2}
\mathrm{CO}_{3}\). What is the value of \(x\) ?