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After 0.6 g of CoCl2 x 6H20 is heated, the residue has a mass of 0.339 g. Calculate the % H2O in the hydrate. What was the actual number of moles of water per formula unit CoCl2?

Respuesta :

a.) 0.6g-0.339g=0.261g

(0.261g / 0.6g) x 100%= 43.5%

b.) (1 mol CoCl2 / 129.83 g) x (6.022 x 10^23 / 1 mol CoCl2)= 4.638 x 10^21

Part a.) uses knowledge about percent recovery and part b.) uses knowledge of converting 1 mol of a substance to formula units

Eduard22sly

A. The percentage of water, Hâ‚‚O in the hydrate is 43.5%

B. The actual number of mole of water per formula unit CoClâ‚‚ is 6 moles

A. How to determine the percentage of water

From the question given above, the following data were obtained:

  • Mass of hydrate, CoCl₂•xHâ‚‚O = 0.6 g
  • Mass of anhydrous, CoClâ‚‚ = 0.339 g
  • Mass of water = 0.6 – 0.339 = 0.261 g
  • Percentage of water =?

Percentage of water = (mass of H₂O / mass of CoCl₂•xH₂O) × 100

Percentage of water = (0.261 / 0.6) × 100

Percentage of water = 43.5%

B. How to determine the mole of water per formula unit

To obtain the mole of water per formula unit CoClâ‚‚, we shall determine the formula of the hydrate. This can be obtained as follow:

  • Percentage of Hâ‚‚O = 43.5%
  • Percentage of CoClâ‚‚ = 100 – 43.5 = 56.5
  • Formula =?

Divide by their molar mass

CoClâ‚‚ = 56.5 / 130 = 0.4

Hâ‚‚O = 43.5 / 18 = 2.4

Divide by the smallest

CoClâ‚‚ = 0.4 / 0.4 = 1

Hâ‚‚O = 2.4 / 0.4 = 6

Thus, the formula of the hydrate is CoCl₂•6H₂O

Therefore, the mole of water per formula unit CoClâ‚‚ is 6 moles

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