Question

Write the correct formula for the compound formed by each of the following pairs of ions.

1.) Ni^2+, SO4^2-
2.) Al^3+, O^2-
3.) Ca^2, ClO3-
4.) NH4+, P^3-
5.) Cu+, NO3-

Answer 1

1.) NiSO₄; 2.) Al₂O₃; 3.) Ca(ClO₃)₂; 4.) (NH₄)₃P; 5.) CuNO₃

Step-by-step explanation:

We can use the criss-cross method to work out the formulas. The steps are

1. Write the symbols of the anion and cation.
2. Criss-cross the numbers of the charges to become the subscripts of the other ion (as in the image).
3. Write the formula with the new subscripts.
4. Divide the subscripts by their highest common factor.
5. Omit all subscripts that are 1.

If we use this method, the formula for the compound formed from Na⁺, SO₃²⁻ becomes Na₂SO₃.

1.) Ni²⁺ + SO₄²⁻ ⟶ Ni₂(SO₄)₂ ⟶ NiSO₄

2.) Al³⁺ + O²⁻ ⟶ Al₂O₃

3.) Ca²⁺ + ClO₃⁻ ⟶ Ca(ClO₃)₂

4.) NH₄⁺ + P³⁻ ⟶ (NH₄)₃P

5.) Cu⁺ + NO₃⁻ ⟶ CuNO₃