Answer to Question #132046 in Inorganic Chemistry for Bella

Question #132046
Barium hydroxide crystallises as one of several possible hydrates. A sample of barium hydroxide is analysed in order to determine its formula. 3.632 g of the sample was dissolved in water to make 250.0 mL of solution. 25.00 mL of this solution was titrated with 0.0987 M HCl, using methyl orange indicator. Titres of 23.26, 23.29 and 23.34 mL were obtained.

Determine the formula (that is, find the value of x) of the barium hydroxide sample.
1
Expert's answer
2020-09-08T05:57:57-0400

Step I : Get the average titre of the acid


Step II : Calculate moles of HCl in this volume


We know that, concentration of the acid is 0.0987M





These are the moles of HCl that reacted with barium hydroxide solution.


Step III : Write balanced equation for the reaction and calculate moles of barium hydroxide that reacted.

Ba(OH)2(aq) + 2HCl(aq) BaCl2(aq) + 2H2O(l)


From the reaction mole ratio (Moles of base:moles of acid) is 1:2

Meaning 1 mole of Ba(OH)2 reacts with 2 moles of HCl



These moles of Ba(OH)2 were in 25cm3

How many moles were there in the 250cm3 of the stock solution?

By cross multiplication we get;


These were the number of moles in the 3.632g of solid sample that was dissolved.


Step IV : Calculate RFM of the solid sample of Ba(OH)2 . xH2O


From the formula; we get,




Step V : Now Determine the value of x in Ba(OH)2. xH2O


(Atomic mass, Ba=137.3, H=1.0, O=16.0)


Ba(OH)2.xH2O = 315.911083


173.3 + 2(16+1) + x(2+16) = 315.911083

137.3 + 34 + 18x = 315.911083


18x = 315.911083 - 171.3

18x = 144.61

Divide both sides by 18

The value of x is approximately 8

The formula of hydrated barium hydroxide is therefore Ba(OH)2 . 8H2O

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