ANSWER TO QUESTION 1

A 1 molar solution contains 1 mole of solute in a 1 L solution.

The mole (symbol: mol) is a unit that measures an amount of substance. One mole contains approximately 6.022×10²³ entities; in the context of this question, it measures the number of iron ions.

Question:

1. Calculate how much iron (III) chloride we need to get 10 ml a 1 molar solution of iron (III)?
2. How many mol iron (II) is needed to get Fe₃O₄?

Help: (Molecular weight of iron(III)chloride hexahydrate is 270.3 g/mol)

Answer:

1.

For 1 L 1 molar iron (III) chloride solution we need 1 mol iron chloride.

For 10 mL we need 0.01 mol iron chloride.

1 mol is 270.3 g ==> 0.01 mol is 0.01 mol * 270.3 g/mol = 2.703 g

We have to weigh 2.703 g iron (III) chloride in 10 ml of water. Instead of using water we use here a 1 molar solution of hydrochloric acid.

2.

In Fe3O4 we have the double amount of iron (III) than iron (II). Therefore we need only the half of the iron (II) ions in the solution. In 10 mL of 0.01 molar iron (III) chloride solution we have 0.01 mol iron (III) ions. Therefore we need only 0.005 mol iron (II) ions.

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