Question

Give an 3 example of precipitation reaction.

Answer 1

precipitation eg. are rain , sleet, hail, snow,etc.

Answer 2

recipitation reaction occurs.

Applications and Examples
Precipitation reactions are useful in determining whether a certain element is present in a solution. If a precipitate is formed when a chemical reacts with lead, for example, the presence of lead in water sources could be tested by adding the chemical and monitoring for precipitate formation. In addition, precipitation reactions can be used to extract elements, such as magnesium from seawater. Precipitation reactions even occur in the human body between antibodies and antigens; however, the environment in which this occurs is still being studied.

EXAMPLE 1

Complete the double replacement reaction and then reduce it to the net ionic equation.

NaOH(aq)+MgCl2(aq)→(1.2)
First, predict the products of this reaction using knowledge of double replacement reactions (remember the cations and anions “switch partners”).

2NaOH(aq)+MgCl2(aq)→2NaCl+Mg(OH)2(1.3)
Second, consult the solubility rules to determine if the products are soluble. Group 1 cations ( Na+ ) and chlorides are soluble from rules 1 and 3 respectively, so NaCl will be soluble in water. However, rule 6 states that hydroxides are insoluble, and thus Mg(OH)2 will form a precipitate. The resulting equation is the following:

2NaOH(aq)+MgCl2(aq)→2NaCl(aq)+Mg(OH)2(s)(1.4)
Third, separate the reactants into their ionic forms, as they would exist in an aqueous solution. Be sure to balance both the electrical charge and the number of atoms:

2Na+(aq)+2OH−(aq)+Mg2+(aq)+2Cl−(aq)→Mg(OH)2(s)+2Na+(aq)+2Cl−(aq)(1.5)
Lastly, eliminate the spectator ions (the ions that occur on both sides of the equation unchanged). In this case, they are the sodium and chlorine ions. The final net ionic equation is:

Mg2+(aq)+2OH−(aq)→Mg(OH)2(s)(1.6)
EXAMPLE 2

Complete the double replacement reaction and then reduce it to the net ionic equation.

CoCl2(aq)+Na2SO4(aq)→(1.7)
SOLUTION

The predicted products of this reaction are CoSO4 and NaCl . From the solubility rules, CoSO4 is soluble because rule 4 states that sulfates ( SO2−4 ) are soluble. Similarly, we find that NaCl is soluble based on rules 1 and 3. After balancing, the resulting equation is as follows:

CoCl2(aq)+Na2SO4(aq)→CoSO4(aq)+2NaCl(aq)(1.8)
Separate the species into their ionic forms, as they would exist in an aqueous solution. Balance the charge and the atoms. Cancel out all spectator ions (those that appear as ions on both sides of the equation.):

Co2- (aq) + 2Cl-(aq) + 2Na+ (aq) + SO42-(aq) → Co2- (aq) + SO42-(aq) + 2Na+ (aq) + 2Cl-(aq)