Question

Excess of naoh (aq) was added to 100 ml of fecl3 (aq) resulting into 2.14 g of fe(oh)3 . the molarity of fecl3 (aq) is :

Answer 1

We first write the equation of reaction :

3NaOH (aq) + FeCl₃ (aq) —> 3NaCl (aq) + F(OH)₃ (aq)

The mole ratio between FeCl₃ and Fe(OH) ₃ is 1 : 1

Moles in Fe(OH) ₃ is :

Molar mass of Fe(OH) ₃ = 56 + 48 +3 = 107 grams / moles

Moles = mass / molar mass

2.14 g / (107g / mole) = 0.02 moles.

Since the mole ratio is 1 : 1, the moles of FeCl₃ is 0.02moles.

Molarity = moles per litre

0.02 moles are in 100ml, how many moles are in 1000ml

(1000 / 100) × 0.02 = 0.2 moles / 1000ml

Molarity of FeCl₃ is thus :

0.2 moles per litre

Answer 2

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