0.789g of crystalline barium hydroxide is dissolved in water. For the neutralisation of this solution, 20mL of N4HNO3 is required. How many molecules of water are present in one g mole of this base? (Ba=137.4,O=15,N=14,H=1).
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Solution
Let the molecular formula be Ba(OH)2⋅xH2O Mol. mass of Ba(OH)2⋅xH2O=137.4+(2×16)+(2×1)+18x =171.4+18x Eq. mass of Ba(OH)2⋅xH2O=171.4+18x2 20mLN4HNO3≡20mLN4Ba(OH)2⋅xH2O Amount of Ba(OH)2⋅xH2O=(171.4+18x)2×4×201000 =171.4+18x400g Amount of Ba(OH)2⋅xH2O=0.789g Hence, 171.4+18x400=0.789 or 171.4+18x=0.789×400 x=144.218=8.01=8. Thus, 8g moles of water molecules are present in one g mole of the base.