7. When 2.246 grams of a calcium chloride hydrate was heated, 0.728 grams of wat

Question

7. When 2.246 grams of a calcium chloride hydrate was heated, 0.728 grams of water were released. Determine the formula of the hydrate [Hint: take the same approach as for the copper(II) sulfate hydrate. When 2.50 grams of copper (Cu) reacts with oxygen gas, a copper oxide product is made which has a mass of 2.81 grams. 8. What is the empirical formula of the copper oxide? [Hint: start by finding the mass of each element in the copper oxide]. a. Write a balanced chemical equation for the formation of the copper oxide product from copper metal and oxygen gas. b.

Explanation / Answer

7)

Let the formula of hydrate be CaCl2.XH2O

We need to find the value of X

Molar mass of H2O,

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

= 2*1.008 + 1*16.0

= 18.016 g/mol

mass(H2O)= 0.728 g

number of mol of H2O,

n = mass of H2O/molar mass of H2O

=(0.728 g)/(18.016 g/mol)

= 4.041*10^-2 mol

Molar mass of CaCl2,

MM = 1*MM(Ca) + 2*MM(Cl)

= 1*40.08 + 2*35.45

= 110.98 g/mol

mass(CaCl2)= hydrated mass - mass of water

= 2.246 - 0.728

= 1.518 g

number of mol of CaCl2,

n = mass of CaCl2/molar mass of CaCl2

=(1.518 g)/(110.98 g/mol)

= 1.368*10^-2 mol

X = mol (H2O)/mol (CaCl2)

X = 4.041*10^-2 / 1.368*10^-2

X = 3

So, the formula is

CaCl2.3H2O

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