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2.5 g of a hydrate barium salt gave on heating, 2.13 g of the anhydrous...

Chemistry
JAMB 1983

2.5 g of a hydrate barium salt gave on heating, 2.13 g of the anhydrous salt. Given that the relative molecular mass of the of the anhydrous salt is 208, the number of molecules of water of crystallization of the barium salt is

  • A. 10
  • B. 7
  • C. 5
  • D. 2
  • E. 1
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Correct Answer: Option D
Explanation

Given:

Mass of hydrated Barium salt    = 2.5g

Mass of anhydrous Barium salt = 2.13g 

Molar mass of anhydrous salt =  208

Molar mass of anhydrous salt = 208 + 18x ( 18x due to the unknown molecule of water of crystallization, i.e xH2O, since Molar mass of H2O = 18, then multiplied by X)

To calculate the number of water of crystallization, we use the formula:

  \(\frac{mass of hydrated salt}{mass of anhydrous salt}\) = \(\frac{Molar mass of hydrated salt}{Molar mass of anhydrous salt}\) 

\(\frac{2.5}{2.13}\) = \(\frac{208 + 18x}{208}\)

2.13 (208 + 18x) = 2.5 x 208

443.04 + 38.34x = 520

38.34x = 520 - 443.04

38.34x = 76.96

x = \(\frac{76.96}{38.34}\)

x = 2.00

Therefore, the number of water of crystallization is 2


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