Washing soda is a hydrate of sodium carbonate. its formula is na2co3. x h2o. a 2.714 g sample of washing soda is heated until a constant mass of 1.006 g of na2co3 is reached. what is x ?

1.006 g of Na2CO3 is left; which means that (2.714 -1.006) g of water are lost from the hydrated sodium carbonate

So, water present = (2.714 -1.006) = 1.708 g.

Molecular Wt. of water is =18 g
so moles  = 1.708/18 moles = 0.095 moles. 

Now, Na2CO3 has molecular wt. of = 23x2 + 12 +3x16 = 106 g,

so moles of Na2CO3 =  1.006/106 moles = 0.0095 moles 

Ratio is = 0.0095 / 0.095 = 1 / 10    [ moles of Na2CO3 / moles of H2O ]

Ratio is saying on every 1 mole of Na2CO3 , there are 10 moles of H2O

so x is 10

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