Types of Reactions

In Chemistry, we can identify a lot of different types of chemical reactions. We can put these chemical reactions into groups, so it makes it easier to learn about them. In this standard we will learn about FOUR types of chemical reactions: Precipitation Reactions Displacement Reactions Thermal Decomposition Reactions Combination Reactions

1. Precipitation Reactions If a solute (e.g sugar) dissolves in a solvent (e.g water), the sugar is said to be soluble in water and so a solution is formed. Solubility is the word used to describe how much solute can dissolve in a set volume of solvent before saturation occurs.

Now, when two different ionic solutions are mixed, there is a chance of bringing together two ions that combine to form an insoluble substance. When this happens, you will see a solid forming. This solid is called a precipitate, and the reaction is called a precipitation reaction.

Example Sodium Chloride and Silver Nitrate are both soluble, so we can make solutions of them. However, Silver chloride is insoluble. Therefore, when these two solutions are mixed, the silver ions and chloride ions will join together to form a precipitate of silver chloride. So we will see a white solid form. This is Silver Chloride. The other two ions will remain in the solution as ‘spectators’

How do we know if a Precipitate will form? We need to know the ‘solubility rules’ They are: 1.All nitrates are soluble. 2.All Sulfates are soluble except Barium, Calcium and Lead. 3.All Chlorides and Iodides are soluble except Lead and Silver. 4.All Hydroxides and Carbonates are insoluble except Lithium, Sodium, and Potassium. 5.All Lead salts are insoluble except Lead Nitrate. 6.All Group 1 Metal Salts are soluble

Writing Precipitation Reactions. When writing equations for precipitation reactions, it is best to identify the ions that form the precipitate and leave the spectators out. E.g. NaCl is added to AgNO 3 The Ag + and Cl - ions will form the precipitate. The other two ions are spectators. So the equation is: Ag + (aq) + Cl - (aq)  AgCl (s)

ReactantsPredictionObservation Sodium Hydroxide + Magnesium Sulfate Sodium Hydroxide + Potassium Chloride Sodium Hydroxide + Lead Nitrate Barium Chloride + Copper Sulfate Sodium Hydroxide + Copper Sulfate Lead Nitrate + Potassium Iodide Potassium Iodide + Sodium Hydroxide yes no yes yes yes yes White solid forms No Reaction White solid forms Blue solid forms Yellow solid forms no No Reaction

Sodium Hydroxide + Magnesium Sulfate  Magnesium Hydroxide + Sodium Sulfate Sodium Hydroxide + Potassium Chloride  No Reaction Sodium Hydroxide + Lead Nitrate  Lead Hydroxide + Sodium Nitrate Barium Chloride + Copper Sulfate  Barium Sulfate + Copper Chloride Copper Sulfate + Sodium Hydroxide  Copper Hydroxide + Sodium Sulfate Potassium Iodide + Lead nitrate  Lead iodide + Potassium Nitrate Potassium Hydroxide + Sodium Hydroxide  No Reaction