Question
Which of the following is correct representation of a given molecular equation in ionic form?
$${K_2}C{r_2}{O_7} + 7{H_2}S{O_4} + 6FeS{O_4} \to $$ $$3F{e_2}{\left( {S{O_4}} \right)_3} + C{r_2}{\left( {S{O_4}} \right)_3} + {K_2}S{O_4}$$ $$ + 7{H_2}O$$
A.
$$C{r_2}O_7^{2 - } + 14{H^ + } + 6F{e^{2 + }} \to $$ $$6F{e^{3 + }} + 2C{r^{3 + }} + 7{H_2}O$$
B.
$$2{K^ + } + C{r_2}O_7^{2 - } + 7SO_4^{2 - } + 6F{e^{2 + }}$$ $$ \to 3F{e^{3 + }} + SO_4^{2 - } + C{r^{3 + }} + {K^ + }$$ $$ + 7{H_2}O$$
C.
$$C{r_2}O_7^{2 - } + 2{K^ + } + 7{H^ + } + 6F{e^{2 + }} \to $$ $$6F{e^{3 + }} + 6C{r^{3 + }} + {K^ + }$$
D.
$$C{r_2}O_7^{2 - } + 7{H^ + } + 6F{e^{2 + }} \to $$ $$3F{e^{2 + }} + 2C{r^{3 + }} + 2{K^ + } + 7{H_2}O$$
Answer :
$$C{r_2}O_7^{2 - } + 14{H^ + } + 6F{e^{2 + }} \to $$ $$6F{e^{3 + }} + 2C{r^{3 + }} + 7{H_2}O$$
Solution :
$${K_2}C{r_2}{O_7} + 7{H_2}S{O_4} + 6FeS{O_4} \to $$ $$3F{e_2}{\left( {S{O_4}} \right)_3} + C{r_2}{\left( {S{O_4}} \right)_3} + 7{H_2}O$$ $$ + {K_2}S{O_4}$$
$${\text{In ionic form}}\,:$$
$$2{K^ + } + C{r_2}O_7^{2 - } + 14{H^ + } + 7SO_4^{2 - }$$ $$ + 6F{e^{2 + }} + 6SO_4^{2 - } \to 6F{e^{3 + }} + 9SO_4^{2 - }$$ $$ + 2C{r^{3 + }} + 3SO_4^{2 - } + 2{K^ + } + SO_4^{2 - }$$ $$ + 7{H_2}O$$
$${\text{Eliminating the common species :}}$$
$$C{r_2}O_7^{2 - } + 14{H^ + } + 6F{e^{2 + }} \to $$ $$6F{e^{3 + }} + 2C{r^{3 + }} + 7{H_2}O$$