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7 October, 18:20

Washing soda is a hydrated compound whose formula can be written NA2CO3 xH2O, where x is the number of moles of H2O per mole of Na2CO3. When a 2.123g sample of washing soda was heated at 130*C, all of the water of hydration was lost, leaving the 0.786g of anhydrous sodium carbonate. Calculate the value of x

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  1. 7 October, 20:36
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    The value of X is 10 hence the of hydrated washing soda is Na2CO3.10H2O

    calculation

    Step 1: calculate the mass of water

    = mass of hydrated washing soda - mass of anhydrous sodium carbonate (anhydrous washing soda)

    = 2.123 g - 0.786 g = 1.337 grams

    Step 2: calculate the moles of Na2CO3 and that of H2O using moles=mass/molar mass formula

    molar mass of Na2CO3 = (2x23) + 12 + (16 x3) = 106 g/mol molar mass of H2O = (1 x2) + 16 = 18 g/mol

    = moles of Na2CO3 therefore = 0.786 g/106 g/mol = 0.00742 moles

    moles of H2O = 1.337 g/18 g/mol = 0.0743 moles

    Step 3: find the mole ratio

    that is divide each mole by smallest number of mole (0.00742)

    = for Na2CO3 = 0.00742/0.00742 = 1

    for H2O = 0.0743/0.00742 = 10

    hence the value of X = 10
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