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Precipitation Reaction


When we look around ourselves, we can find a number of reactions occurring in our day to day lives. Some of them being burning of paper or any other material, cooking, digestion, reactions inside a cell or a battery, corrosion, i.e., rusting of iron and many more. So, out of all these, there’s a special type called a precipitation reaction.

What is a precipitation reaction?

In this type of reaction, two soluble salts present in aqueous solution are mixed, and then they react, and the formation of 2 products occur, one of them is soluble in, and the other is not soluble, the product which is not soluble is given a special name, i.e., precipitate.

Precipitation reactions are also sometimes called double displacement reactions. The most known example of the precipitation reaction is the reaction between silver nitrate and potassium chloride resulting in the formation of potassium nitrate, which is soluble and silver chloride is the solid residue called a precipitate.

AgNO3 (aq.) + K Cl (aq.) AgCl (precipitate) + KNO3 (aq.)

Other examples of precipitation reaction:

  • AgNO3 (aq.) + NaCl (aq.) AgCl (pr.) + NaNO3 (aq.)   
  • 2KOH (aq.) + CaCl2 (aq.)   Ca (OH)2 (precipitate) + 2KCl(aq.)
  • Due to the formation of precipitates of magnesium and calcium oxide inside the pipes in our home, they get clogged, and this happens because of hard water.
  • Kidney stones are a precipitate of calcium ions and oxalates, and this is the reason why we all are said to drink a lot of water to avoid the formation of kidney stones as with more water, precipitate dissolves, avoiding the formation of kidney stones.

Properties of Precipitation reaction

1. In this reaction, the reactants are dissolved substances that lead to the formation of one or more solid residue products, and this reaction takes place either in an aqueous solution or any other medium which is in an ionic state.

2. Precipitation reactions are also called ionic reactions because in these reactions exchange of ions takes place, leading to the formation of products.

3. Precipitation reactions vary with factors like temperature, the concentration of the solution etc.

Applications of Precipitation Reactions

1. With the help of these reactions, we can determine which elements are present in the solution using basic concepts like the colour of the residue formed.

2. It is also useful when it comes to the extraction of useful elements like Mg from seawater.

3. It is also used to treat wastewater, which frequently contains heavy metals in the form of compounds of hydroxide and sulfides.

Frequently asked questions

Q1) Does temperature affect the precipitation reactions? If yes, then explain.

Yes, the temperature is a factor on which precipitation reaction depends, and it can decide whether the reaction will take place or not. If we increase the solution's temperature, then the solubility of the ionic compound increases, which improves the chances of the reaction.

Q2) Can we use precipitation reactions to identify compounds? If yes, then how?

Yes, we can use precipitation reactions to identify constituents of a solution. For e.g., if AgNO3 is added to a solution and precipitates forms, then there are high chances that the solution contains Cl- ions.

Q3) Explain how a precipitation reaction is a double displacement reaction.

So, in a precipitation reaction, suppose there are two ionic compounds on the reactant side, and then both dissociates in the aqueous solution. Then, what happens next is that they exchange each other's cation and anions, and the formation of precipitate takes place. This is how it's a double displacement reaction.

Q4) Comment on the solubility of AgBr and iodine in water.

Silver bromide and iodine both are not soluble in water. As we know, the concept of like dissolves like and iodine exists in the form of I2, which is a nonpolar molecule, and water is polar. Therefore iodine is not soluble in water.

Q5) How is the formation of precipitate important?

Through the precipitate formation, we can identify the cations present in the solution by using information like the colour of the precipitate and its solubility in excess.

Q6) Can a single displacement reaction be also called a precipitation reaction?

Yes, it happens when there are more than two metal ions present in the solution, and one is replaced by another, unlike a double displacement reaction in which the exchange of metal ions occurs between 2 salts.

Q7) What is the colour of the following precipitates? – AgBr, AgCl, AgI, AgOH

AgI and AgBr have yellow colour while AgCl has white and AgOH has a brown colour.





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