A precipitation reaction is a reaction that returns an insoluble product—a precipitate—when two solutions are mixed. When a colorless systems of silver- nitrate is blended with a yellow-orange solution of potassium dichromate, a reddish precipitate of silver- dichromate is produced.

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< ce AgNO_3(aq) + K_2Cr_2O_7(aq) ightarrow Ag_2Cr_2O_7(s) + KNO_3(aq) label4.2.1>

This unbalanced equation has the general kind of an exchange reaction:

Thus precipitation reactions are a subclass of exchange reactions that occur in between ionic compounds once one that the products is insoluble. Due to the fact that both components of each compound adjust partners, together reactions are sometimes referred to as double-displacement reactions. Precipitation reactions are usedto isolate steels that have been extracted from your ores, and also to recuperate precious steels for recycling.

Video: mixing potassium dichromate and also silver nitrate together to begin a precipitation reaction (Equation ( ef4.2.1)).

Just as crucial as predicting the product the a reaction is discovering when a centregalilee.comical reaction will not occur. Simply mixing solutions of two various centregalilee.comical substances walk not guarantee that a reaction will certainly take place. Because that example, if 500 mL the aqueous (NaCl) equipment is combined with 500 mL that aqueous (KBr) solution, the last solution has actually a volume of 1.00 L and contains (ceNa^+(aq)), (ceCl^−(aq)), (ceK^+(aq)), and also (ceBr^−(aq)). Together you will view in (Figure (PageIndex1)), no one of these types reacts with any of the others. As soon as these solutions are mixed, the only effect is come dilute each systems with the other.

Figure (PageIndex1): The impact of mixing Aqueous (ceKBr) and also (ceNaCl) Solutions. Because no network reaction occurs, the only effect is to dilute each solution with the other. (Water molecules space omitted indigenous molecular views of the solutions for clarity.)

Predicting Precipitation Reactions

A precipitation reaction occurs when a solid precipitate creates after mixing two solid electrolyte solutions. As stated previously, if no one of the varieties in the equipment reacts climate no network reaction occurred.

Predict what will occur when aqueous services of barium chloride and also lithium sulfate room mixed.

Change the partners of the anions and also cations top top the reactant side to type new compound (products):


Because barium chloride and also lithium sulfate are solid electrolytes, each dissociates fully in water to offer a equipment that consists of the constituent anions and also cations. Mix the two services initially offers an aqueous equipment that contains (ceBa^2+), (ceCl^−), (ceLi^+), and also (ceSO4^2−) ions. The only possible exchange reaction is to kind (ceLiCl) and also (ceBaSO4).

Correct the formulas of the products based upon the dues of the ions.

No have to correct the formula together both compounds currently have their charges balanced.

Refer come the solubility rules table to determine insoluble commodities which will certainly therefore form a precipitate.

< ceBaCl_2(aq) + Li_2SO_4(aq) ightarrow BaSO_4(s) + LiCl(aq) onumber >

Table 7.5.1 from the ahead section mirrors that (ceLiCl) is soluble in water, however (ceBaSO4) is not soluble in water.

Balance the equation:

Although soluble barium salts space toxic, (ceBaSO4) is for this reason insoluble the it can be provided to diagnose stomach and intestinal problems without being absorbed into tissues. An outline of the digestive organs shows up on x-rays of patient who have actually been provided a “barium milkshake” or a “barium enema”—a suspension of an extremely fine (ceBaSO4) particles in water.

Figure (PageIndex2): an x-ray that the digestive organs of a patient who has swallowed a “barium milkshake.” A barium milkshake is a suspension of really fine BaSO4 corpuscle in water; the high atomic mass that barium makes it opaque come x-rays. (Public Domain; Glitzy queen00via Wikipedia).

Example (PageIndex1)

Predict what will take place if aqueous remedies of rubidium hydroxide and also cobalt(II) chloride are mixed.


Steps example

Change the partner of the anions and cations ~ above the reactant side to type new link (products).


Correct the formulas of the products based on the fees of the ions.

(ceRbOH(aq) + CoCl2(aq) ightarrow RbCl+ Co(OH)_2)

Refer come the solubility rule table to recognize insoluble assets which will certainly therefore kind a precipitate.

(ceRbOH(aq) + CoCl_2(aq) ightarrow RbCl(aq) + Co(OH)_2(s))
Balance the equation.

Coefficients currently balanced.

(ceRbOH(aq) + CoCl_2(aq) ightarrow RbCl(aq)+ Co(OH)_2(s))

Example (PageIndex2)

Predict what will take place if aqueous services of strontium bromide and also aluminum nitrate are mixed.


Steps instance

Change the partners of the anions and cations top top the reactant next to form new link (products).


Correct the recipe of the products based on the dues of the ions.

(ceSrBr_2(aq) + Al(NO_3)_3(aq) ightarrow Sr(NO_3)_2 + AlBr_3)

Refer come the solubility rules table to determine insoluble commodities which will certainly therefore kind a precipitate.

(ceSrBr_2(aq) + Al(NO_3)_3(aq) ightarrow Sr(NO_3)_2(aq) + AlBr_3(aq))

According to Table 7.5.1 native the previous section, both (ceAlBr3) (rule 4) and also (ceSr(NO3)2) (rule 2) room soluble.

If all possible products space soluble, then no net reaction will certainly occur.

(ceSrBr_2(aq) + Al(NO_3)_3(aq) ightarrow)


Exercise (PageIndex2)

Using the details in Table 7.5.1 indigenous the previous section, suspect what will take place in each case involving solid electrolytes.

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an aqueous equipment of strontium hydroxide is added to one aqueous systems of iron(II) chloride. Heavy potassium phosphate is included to one aqueous equipment of mercury(II) perchlorate. Solid salt fluoride is included to an aqueous equipment of ammonium formate. Aqueous remedies of calcium bromide and cesium carbonate room mixed. Answer a Fe(OH)2 precipitate is formed. Answer b Hg3(PO4)2 precipitate is formed. Answer c No Reaction. Answer d CaCO3 is precipitate formed.