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Crystals of hydrated sodium carbonate left exposed to the atmosphere gradually lose some of their water of crystallisation. The formula of the crystals may be given by Na(2)CO(3).xH2O where x has a numerical value between 0 and 10. 16 grams of the crystals were dissolved in water and made upto 250cm3 in a standard flask. To determine the value of x, 25cm3 of the sodium carbonate solution were titrated with 1.0M hydrochloric acid. 15cm3 of the acid was required for neutralisation.

(1) Calculate the mass of sodium carbonate (Na(2) CO(3)) in 16 grams of the crystals.

(2) Calculate the value of x in the formula Na(2)CO(3).xH2O

Any help would be greatly appreciated. Thanks,

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OK this is a volumetric analysis question, which always goes like this

step 1: calculate number of moles of known substance used

step 2: use stoichiometry to find number of moles of unknown substance used

step 3: use information from step 2 to find whatever it was you were asked for

step 1 is simple. find the number of moles of HCl. This involves the equation c = n/V

step 2 requires you to write a balanced equation for the reaction of [ce]Na2CO3[/ce] with HCl (remember that the waters of crystallization will not be involved in this reaction so you can leave them out).

step 3 involves using the number of moles of [ce]Na2CO3[/ce] from step 2, along with the original mass of the solid with the waters of crystallization to calculate the value of x in [ce]Na2CO3.xH2O[/ce]

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