# How would you balance the following double replacement equation: Al(NO3)3 + Na3PO4 = AlPO4 + NaNO3?

$A l {\left(N {O}_{3}\right)}_{3} \left(a q\right) + N {a}_{3} P {O}_{4} \left(a q\right) \rightarrow A l \left(P {O}_{4}\right) \left(s\right) \downarrow + 3 N a N {O}_{3} \left(a q\right)$
All nitrates are soluble; all salts of the alkali metals are soluble; all phosphates are insoluble. This is as far as I know; I will just look up at the solubility of aluminum phosphate. Wiki tells me it has a ${K}_{s p} = 6.3 \times {10}^{- 19}$; so rules of thumb are entirely appropriate here.