Exercise 9.10
Complete the Table by writing the formulae of the compounds formed by the cations on the left and the anions at the top. is given as an example. +
Disagrees with the book
This working does not reach the answer printed in NCERT. One of the two is wrong and it has not yet been settled which — check it before you rely on it.
NCERT’s answer
\(\displaystyle NO_{3}\) \(\displaystyle SO_{4}\) \(\displaystyle PO_{4}\) $\displaystyle 2$− $\displaystyle 3$− + \(\displaystyle NH_{4}\) \(\displaystyle NH_{4}\)\(\displaystyle NO_{3}\) (\(\displaystyle NH_{4}\))\(\displaystyle 2SO_{4}\) (\(\displaystyle NH_{4}\))\(\displaystyle 3PO_{4}\) \(\displaystyle Li^{+}\) \(\displaystyle LiNO_{3}\) \(\displaystyle Li_{2}\)\(\displaystyle SO_{4}\) \(\displaystyle Li_{3}\)\(\displaystyle PO_{4}\) \(\displaystyle Al^{3+}\) Al(\(\displaystyle NO_{3}\))$\displaystyle 3$ \(\displaystyle Al_{2}\)(\(\displaystyle SO_{4}\))$\displaystyle 3$ \(\displaystyle AlPO_{4}\) \(\displaystyle Cu^{2+}\) Cu(\(\displaystyle NO_{3}\))$\displaystyle 2$ \(\displaystyle CuSO_{4}\) \(\displaystyle Cu_{3}\)(\(\displaystyle PO_{4}\))$\displaystyle 2$ $\displaystyle 272$ Textbook of Science for Grade $\displaystyle 9$
The completed table:
| Cation | \(\displaystyle NO_3^-\) | \(\displaystyle SO_4^{2-}\) | \(\displaystyle PO_4^{3-}\) |
| \(\displaystyle NH_4^+\) | \(\displaystyle NH_4NO_3\) | \(\displaystyle (NH_4)_2SO_4\) | \(\displaystyle (NH_4)_3PO_4\) |
| \(\displaystyle Li^+\) | \(\displaystyle LiNO_3\) (given) | \(\displaystyle Li_2SO_4\) | \(\displaystyle Li_3PO_4\) |
| \(\displaystyle Al^{3+}\) | \(\displaystyle Al(NO_3)_3\) | \(\displaystyle Al_2(SO_4)_3\) | \(\displaystyle AlPO_4\) |
| \(\displaystyle Cu^{2+}\) | \(\displaystyle Cu(NO_3)_2\) | \(\displaystyle CuSO_4\) | \(\displaystyle Cu_3(PO_4)_2\) |
Method for every cell: criss-cross the charge numbers, then divide the subscripts by a common factor if there is one.
\(\displaystyle Al^{3+}\) with \(\displaystyle PO_4^{3-}\) gives \(\displaystyle Al_3(PO_4)_3\), which reduces to \(\displaystyle AlPO_4\); \(\displaystyle Cu^{2+}\) with \(\displaystyle SO_4^{2-}\) gives \(\displaystyle Cu_2(SO_4)_2\), which reduces to \(\displaystyle CuSO_4\).
Brackets are written only where two or more of the same polyatomic ion appear — so \(\displaystyle Al(NO_3)_3\) and \(\displaystyle (NH_4)_2SO_4\) take them, while \(\displaystyle NH_4NO_3\) and \(\displaystyle AlPO_4\) do not.