Q.49E - Chemistry (OpenStax)

Question

For each of the following pairs of ions, write the symbol for the formula of the compound they will form:

1. \(C{a^{2 + }},{S^{2 - }}\)
2. \(NH_4^ + ,SO_4^{2 - }\)
3. \(A{l^{3 + }},B{r^ - }\)
4. \(N{a^ + },HPO_4^{2 - }\)
5. \(M{g^{2 + }},PO_4^{3 - }\)

Step-by-Step Solution

Answer

1. \(CaS\)
2. \({\left( {N{H_4}} \right)_2}S{O_4}\)
3. \(AlB{r_3}\)
4. \(N{a_2}HP{O_4}\)
5. \(M{g_3}{\left( {P{O_4}} \right)_2}\)

Step 1. Finding the way to combine ions

Since the overall charge of a compound is zero, we can combine ions by balancing their charges.

Step 2. Balancing the charges in each part

a. \(C{a^{2 + }},{S^{2 - }}\)\( \to \) +2 charge in 1 Ca atom can balance -2 charge in 1 S atom. Hence, formula becomes\(CaS\).

b. \(NH_4^ + ,SO_4^{2 - }\)\( \to \) Since ammonium ion has only +1 charge, we will be needing 2 molecules of ammonium ion to balance -2 charge in sulphate ion. . Hence the formula of compound becomes\({\left( {N{H_4}} \right)_2}S{O_4}\).

 

c. \(A{l^{3 + }},B{r^ - }\)\( \to \) 3 atoms of Br will be required to balance +3 charge in aluminium ion. . Hence the formula of compound becomes \(AlB{r_3}\).

 

d. \(N{a^ + },HPO_4^{2 - }\)\( \to \) -2 charge in 1 molecule of hydrogen phosphate can be neutralized by 2 atoms of sodium. . Hence the formula of compound becomes\(N{a_2}HP{O_4}\).

 

e. \(M{g^{2 + }},PO_4^{3 - }\)\( \to \) Using cross-multiplying method, we can conclude that charge in 3 atoms of Mg will be balancing charge in 2 molecules of phosphate ion. Hence the formula of compound becomes\(M{g_3}{\left( {P{O_4}} \right)_2}\).