Question 4.9: Balancing a Chemical Equation . Balance this equation:

We can begin by balancing the Na^+ ions. We put a 3 in front of Na_{2} SO_{3} and a 2 in front of Na_{3} PO_{4}   , giving us six Na^+ ions on each side:

There are now three SO_{3} ^{2-} units on the left and only one on the right, so we put a 3 in front of H_{2} SO_{3} :

Now let‘s look at the PO_{4} ^{3-}  units. There are two PO_{4} ^{3-}  units on the right, but only one on the left. To balance them, we put a 2 in front of H_{3} PO_{4} . In doing so, we balance not only the PO_{4} ^{3-}  units but also the hydrogens, and arrive at the balanced equation: