We’re asked to determine the value of x in washing soda, (Na2CO3•xH2O), if heating a 2.814 -g sample leaves 1.04 g of Na2CO3.
Recall that hydrates such as washing soda lose its water of hydration upon heating.
This means that to solve for x which is the number moles of H2O per mole Na2CO3, we need to do the following steps:
Step 1: Determine the mass of water of hydration, H2O evaporated :
Mass H2O = Na2CO3•xH2O - mass Na2CO3
Step 2: Determine the moles of H2O and Na2CO3 to solve for x
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 Na2 CO3 xH2 O, where x is the number of moles of H2 O per mole of Na2 CO3. When a 2.814 -g sample of washing soda is heated at 25 oC, all the water of hydration is lost, leaving 1.04 g of Na2 CO3.
What is the value of x?
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