Question

IF 23 g of FeCl2 reacts with 41g Na3PO4 what is the limiting reactant?

Answer 1

First, we need to figure the reaction out.

Both reactants are ionic compounds, so their reaction is probably a double displacemente reaction.

The Cl has a charge of 1-, so Fe has a charge of 2+. Na has a charge of +1 and PO₄ has a charge of 3-.

To combine Fe²⁺ with PO₄³⁻, we will need 3 Fe²⁺ and 2 PO₄³⁻, so the compound becomes neutral.

Both Na and Cl have single charge, so their combination is simply 1 Na and 1 Cl.

So, the products are Fe₃(PO₄)₂ and NaCl, so the unbalanced reaction is:

`FeCl_2+Na_3PO_4\to Fe_3(PO_4)_2+NaCl`

To balance it, We can start by putting a coefficient of 2 on Na₃PO₄, so we have two PO₄³⁻ anions on both sides:

`FeCl_2+2Na_3PO_4\to Fe_3(PO_4)_2+NaCl`

Now, we put a coefficient of 3 on FeCl₂ and 6 on NaCl to get the balanced equation:

`3FeCl_2+2Na_3PO_4\to Fe_3(PO_4)_2+6NaCl`

Now, we first need to calculate the number of moles of each reactant, using their molar masses:

So:

`\begin{gathered} M_{FeCl_(2)}=\frac{m_(FeCl_2)}{n_{FeCl_(2)}} \\ n_(FeCl_2)=\frac{m_(FeCl_2)}{M_{FeCl_(2)}}=(23g)/(126.751g/mol)=0.181458\ldots mol \end{gathered}`
`\begin{gathered} M_(Na_3PO_4)=\frac{m_(Na_3PO_4)}{n_{Na_(3)PO_(4)}} \\ n_(Na_3PO_4)=\frac{m_(Na_3PO_4)}{M_{Na_(3)PO_(4)}}=(41g)/(163.9406698g/mol)=0.250090\ldots mol \end{gathered}`

Now, if the coefficient of FeCl₂ is 3, for each 3 FeCl₂ that reacts, one reaction occurs, so the number of reactions that will need to occur to consume all its number of moles is that amount over 3:

`n_{\text{reaction}}=(n_(FeCl_2))/(3)=(0.181458\ldots mol)/(3)=0.060486\ldots mol`

Similarly, we get the number of reactions that would occur if all Na₃PO₄ reacts by dividing its number of moles by its coefficient, that is 2:

`n_{\text{reaction}}=(n_(Na_3PO_4))/(2)=(0.250090\ldots mol)/(2)=0.125045\ldots mol`

This means that the amount we have of FeCl₂ is enough for only about 0.0605 mol of reactions while the amount we have of Na₃PO₄ is enought for about 0.1250 mol of reactions, which is more than the other reactant.

This means that the reactant that limits the amount of reaction that can occur is FeCl₂, so the limiting reactant is FeCl₂.