ANSWER TO QUESTION 3

Question:

Instead of using ammonium hydroxide, you can also use sodium hydroxide (NaOH). What are the rection produchts then? Try to write down the formula for this reaction in the same way like for ammonium hydroxide.

Answer:

If you use sodium hydroxide we will get sodium chloride instead of ammoniumchloride.

If we want to write down the formula for this reaction, we will first write down the substances we have at the begin.

We start with FeCl₃ and FeCl₂ and we will add NaOH.

We know we will precipitate Magnetite Fe₃O₄.

x FeCl₃ + x FeCl₂ + x NaOH → x Fe₃O₄+ x NaCl

First we adjust the number of iron (II) and iron (III) of each site. In Magnetite Fe₃O₄ we have the ratio of iron (II) to iron (III) of 1:2.

Therefore we add 1 in front of FeCl₂and 2 in front of FeCl₃.

2 FeCl₃ + FeCl₂ + x NaOH → Fe₃O₄+ x NaCl

Now look at the chloride ions. We have twice three in iron (III) chloride and 2 in iron(II) chloride. This means at the right site we have eight and only on at the left site. Therefore we add the coefficient eight in front of sodium chloride.

2 FeCl₃ + FeCl₂ + x NaOH → Fe₃O₄+ 8 NaCl

Now we have eight sodium ions at the right hand site and only one at the left hand site. Therefore we have to add the coefficient eight in front of sodium hydroxide.

2 FeCl₃ + FeCl₂ + 8 NaOH → Fe₃O₄+ 8 NaCl

Now we have to count everything.

I will note the right site in brackets

2 (2) Iron (III)- ions

1(1) iron (II) - ions

8 (8) chloride - ions

8 (8) sodium -ions

8 (4) oxygen - ions

8 (0) hydrogen -ions

There are 4 oxygenions and 8 hydrogens ions missing on the right hand site. Do you know any substance with the ratio of hydrogen to oxygen 2:1?

Water has this ratio. Therefore we add 4 water on the site of the products.

Now we have our reaction formula:

2 FeCl₃ + FeCl₂ + 8 NaOH → Fe₃O₄ + 8 NaCl + 4 H₂O

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