1. **State the problem:** Write the reaction between hydrochloric acid (HCl) and sodium phosphate (Na3PO4) and determine if a reaction occurs. 2. **Identify ions:** - HCl dissociates into $\mathrm{H^+}$ and $\mathrm{Cl^-}$. - Na3PO4 dissociates into $\mathrm{Na^+}$ and $\mathrm{PO_4^{3-}}$. 3. **Write possible products by combining cations and anions:** - $\mathrm{H^+}$ with $\mathrm{Cl^-}$ forms HCl (acid). - $\mathrm{Na^+}$ with $\mathrm{Cl^-}$ forms NaCl (salt). - $\mathrm{H^+}$ with $\mathrm{PO_4^{3-}}$ forms H3PO4 (phosphoric acid). - $\mathrm{Na^+}$ with $\mathrm{PO_4^{3-}}$ forms Na3PO4 (sodium phosphate). 4. **Check solubility:** All these compounds (HCl, NaCl, H3PO4, Na3PO4) are soluble in water. 5. **Conclusion:** Since all products remain dissolved and no precipitate or gas forms, this is a **no reaction (NR)** situation. **Final reaction:** $$\mathrm{HCl (aq) + Na_3PO_4 (aq) \rightarrow NR}$$ This matches observations that mixing these solutions does not produce a visible reaction or precipitate.