# 2.5.5: Classifying Chemical Reactions (Precipitation) (Problems)

PROBLEM $$\PageIndex{1}$$

Aqueous hydrogen fluoride (hydrofluoric acid) is used to etch glass and to analyze minerals for their silicon content. Hydrogen fluoride will also react with sand (silicon dioxide).

1. Write an equation for the reaction of solid silicon dioxide with hydrofluoric acid to yield gaseous silicon tetrafluoride and liquid water.
2. The mineral fluorite (calcium fluoride) occurs extensively in Illinois. Solid calcium fluoride can also be prepared by the reaction of aqueous solutions of calcium chloride and sodium fluoride, yielding aqueous sodium chloride as the other product. Write complete and net ionic equations for this reaction.

$$\ce{4HF}(aq)+\ce{SiO2}(s)\rightarrow \ce{SiF4}(g)+\ce{2H2O}(l)$$

complete ionic equation: $$\ce{2Na+}(aq)+\ce{2F-}(aq)+\ce{Ca^2+}(aq)+\ce{2Cl-}(aq)\rightarrow \ce{CaF2}(s)+\ce{2Na+}(aq)+\ce{2Cl-}(aq)$$

net ionic equation: $$\ce{2F-}(aq)+\ce{Ca^2+}(aq)\rightarrow \ce{CaF2}(s)$$

PROBLEM $$\PageIndex{2}$$

From the balanced molecular equations, write the complete ionic and net ionic equations for the following:

1. $$\ce{K2C2O4}(aq)+\ce{Ba(OH)2}(aq)\rightarrow \ce{2KOH}(aq)+\ce{BaC2O2}(s)$$
2. $$\ce{Pb(NO3)2}(aq)+\ce{H2SO4}(aq)\rightarrow \ce{PbSO4}(s)+\ce{2HNO3}(aq)$$
3. $$\ce{CaCO3}(s)+\ce{H2SO4}(aq)\rightarrow \ce{CaSO4}(s)+\ce{CO2}(g)+\ce{H2O}(l)$$

$$\ce{2K+}(aq)+\ce{C2O4^2-}(aq)+\ce{Ba^2+}(aq)+\ce{2OH-}(aq)\rightarrow \ce{2K+}(aq)+\ce{2OH-}(aq)+\ce{BaC2O4}(s)\hspace{20px}\ce{(complete)}$$

$$\ce{Ba^2+}(aq)+\ce{C2O4^2-}(aq)\rightarrow \ce{BaC2O4}(s)\hspace{20px}\ce{(net)}$$

$$\ce{Pb^2+}(aq)+\ce{2NO3-}(aq)+\ce{2H+}(aq)+\ce{SO4^2-}(aq)\rightarrow \ce{PbSO4}(s)+\ce{2H+}(aq)+\ce{2NO3-}(aq)\hspace{20px}\ce{(complete)}$$

$$\ce{Pb^2+}(aq)+\ce{SO4^2-}(aq)\rightarrow \ce{PbSO4}(s)\hspace{20px}\ce{(net)}$$

$$\ce{CaCO3}(s)+\ce{2H+}(aq)+\ce{SO4^2-}(aq)\rightarrow \ce{CaSO4}(s)+\ce{CO2}(g)+\ce{H2O}(l)\hspace{20px}\ce{(complete)}$$

$$\ce{CaCO3}(s)+\ce{2H+}(aq)+\ce{SO4^2-}(aq)\rightarrow \ce{CaSO4}(s)+\ce{CO2}(g)+\ce{H2O}(l)\hspace{20px}\ce{(net)}$$

PROBLEM $$\PageIndex{3}$$

Use the following equations to answer the next five questions:

1. $$\ce{H2O}(s)\rightarrow \ce{H2O}(l)$$
2. $$\ce{Na+}(aq)+\ce{Cl-}(aq)\ce{Ag+}(aq)+\ce{NO3-}(aq) \rightarrow \ce{AgCl}(s)+\ce{Na+}(aq)+\ce{NO3-}(aq)$$
3. $$\ce{CH3OH}(g)+\ce{O2}(g)\rightarrow \ce{CO2}(g)+\ce{H2O}(g)$$
4. $$\ce{2H2O}(l)\rightarrow \ce{2H2}(g)+\ce{O2}(g)$$
5. $$\ce{H+}(aq)+\ce{OH-}(aq)\rightarrow \ce{H2O}(l)$$
1. Which equation describes a physical change?
2. Which equation identifies the reactants and products of a combustion reaction?
3. Which equation is not balanced?
4. Which is a net ionic equation?

i. $$H_2O (solid) → H_2O(liquid)$$

iii.

iii. $$\ce{2CH3OH}(g)+\ce{3O2}(g)\rightarrow \ce{2CO2}(g)+\ce{4H2O}(g)$$

v.

PROBLEM $$\PageIndex{4}$$

Write the molecular, total ionic, and net ionic equations for the following reactions:

1. $$\ce{Ca(OH)2}(aq)+\ce{HC2H3O2}(aq)\rightarrow$$
2. $$\ce{H3PO4}(aq)+\ce{CaCl2}(aq)\rightarrow$$

molecular: $$\ce{Ca(OH)2}(aq)+\ce{2HC2H3O2}(aq)\rightarrow \ce{Ca(C2H3O2)2}(aq)+\ce{2H2O}(l)$$

complete ionic: $$\ce{Ca^2+}(aq)+\ce{2OH^-}(aq)+\ce{2H^+}(aq)+\ce{2C2H3O2^-}(aq)\rightarrow \ce{Ca^2+}(aq)+\ce{2C2H3O2^-}(aq)+\ce{2H2O}(l)$$

net ionic: $$\ce{2OH^-}(aq)+\ce{2H^+}(aq)\rightarrow \ce{2H2O}(l)$$

molecular: $$\ce{2H3PO4}(aq)+\ce{3CaCl2}(aq)\rightarrow \ce{Ca3(PO4)2}(s)+\ce{6HCl}(aq)$$

complete ionic: $$\ce{6H^+}(aq)+\ce{2PO4^3-}(aq)+\ce{3Ca^2+}(aq)+\ce{6Cl^-}(aq)\rightarrow \ce{Ca3(PO4)2}(s)+\ce{6H^+}(aq)+\ce{6Cl^-}(aq)$$

net ionic: $$\ce{2PO4^3-}(aq)+\ce{3Ca^2+}(aq)\rightarrow \ce{Ca3(PO4)2}(s)$$

PROBLEM $$\PageIndex{5}$$

Great Lakes Chemical Company produces bromine, Br2, from bromide salts such as NaBr, in Arkansas brine by treating the brine with chlorine gas. Write a balanced equation for the reaction of NaBr with Cl2.

$$\ce{2NaBr}(aq)+\ce{Cl2}(g)\rightarrow \ce{2NaCl}(aq)+\ce{Br2}(l)$$