Question

Which of the following is the correct formula for copper (I) sulfate trihydrate? CuSO4 · 3H2O

Answer 1

Answer:

                   Cu₂SO₄ · 3 H₂O

Explanation:

                         First of all we should be interested in the oxidation number carried out by Copper atom because it can exist both in +1 and +2 state. Hence, as shown in name i.e. (I), it shows that copper is having +1 oxidation state.

                          Secondly, we should be interested in the charge carried out by sulfate ion, as it is conjugate base of sulfuric acid so, it must contain a charge of -2.

                           Therefore, to neutralize -2 charge of SO₄²⁻ ion we have to add two Cu⁺¹ ions hence,

                                             Cu₂SO₄

Furthermore, the number of water molecules are three as the word tri- specifies three.

                                        Cu₂SO₄ . 3 H₂O

Remember:

                    In naming ionic compounds the positive part is named first followed by negative ion.

Answer 2

It is either the 3rd answer or the 4th answer. Both are correct ways to write hydrates, but I was taught the 4th way. Just make sure this answer matches the format of the examples your teacher gave you.