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 Na₂CO₃⋅xH₂O, where x is the number of moles of H₂O per mole of Na₂CO₃. When a 3.837 - g sample of washing soda is heated at 25 ∘C, all the water of hydration is lost, leaving 1.42 g of Na₂CO₃.

What is the value of x?

moles H₂O = 10

Explanation:

The mass of Na₂CO₃⋅xH₂O is 3.837 g and the mass of Na₂CO₃ is 1.42g

Therefore the mass of xH₂O is 3.837 - 1.42 = 2.417 g

The molar mass of Na₂CO₃ is 106 g/mol and for H₂O is 18 g/mol

The moles of Na₂CO₃ and H₂O in the sample are:

Na₂CO₃ = 1.42 / 106 = 0.01340 moles

H₂O = 2.417 / 18 = 0.1343

Now using rule of three:

1 mole of Na₂CO₃ has x moles of H₂O

0.01340 moles of Na₂CO₃ has 0.1343 moles of H₂O

x = 1 * 0.1343 / 0.01340 = 10