Question

A 39.09 gram sample of a hydrate of CoSO4 was heated thoroughly in a porcelain crucible,...

A 39.09 gram sample of a hydrate of CoSO4 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 23.03 grams of the dehydrated compound remained. What is the formula of the hydrate?

Homework Answers

Answer #1

let the formula be CoSO4.xH2O

mass of = H2O = mass of hydrated salt - mass of anhydrous salt

mass of = H2O = 39.09 g - 23.03 g

mass of = H2O = 16.06 g

Molar mass of H2O,

MM = 2*MM(H) + 1*MM(O)

= 2*1.008 + 1*16.0

= 18.016 g/mol

mass(H2O)= 16.06 g

number of mol of H2O,

n = mass of H2O/molar mass of H2O

=(16.06 g)/(18.016 g/mol)

= 0.8914 mol

Molar mass of CoSO4,

MM = 1*MM(Co) + 1*MM(S) + 4*MM(O)

= 1*58.93 + 1*32.07 + 4*16.0

= 155 g/mol

mass(CoSO4)= 23.03 g

number of mol of CoSO4,

n = mass of CoSO4/molar mass of CoSO4

=(23.03 g)/(155 g/mol)

= 0.1486 mol

X = mol (H2O)/mol (CoSO4)

X = 0.8914 / 0.1486

X = 6

so,

the formula be CoSO4.6H2O

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