- Some chemical compounds will dissolve in water, and some will not. Sometimes, two compounds that dissolve in water will react to form a new compound that is insoluble (does not dissolve). This new compound comes out of solution and is referred to as a precipitate.
- In this lab, you will react alum with ammonia. These are both compounds that dissolve in water. Household ammonia contains ammonium hydroxide. The hydroxide part of the chemical reacts with the aluminum in the alum. One of the products of this reaction is the white, insoluble gel called aluminum hydroxide. The aluminum hydroxide will then form a precipitate, and come out of solution.
MATERIALS NEEDED:
1/2 teaspoon alum
2 teaspoons household ammonia
Water
Measuring spoons
Spoon to stir
Small baby food jarPROCEDURE:
Fill the jar one-half full with water.
Add 1/2 teaspoon alum to the water and stir.
Stir in 2 tablespoons of ammonia. CAUTION: ammonia has strong fumes, be careful not to breathe the fumes.Allow the solution to stand for 5 minutes. Observe the formation of the aluminum hydroxide precipitate. As it sits, the precipitate will settle to the bottom of the jar.
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- In this lab, you will react alum with ammonia. These are both compounds that dissolve in water. Household ammonia contains ammonium hydroxide. The hydroxide part of the chemical reacts with the aluminum in the alum. One of the products of this reaction is the white, insoluble gel called aluminum hydroxide. The aluminum hydroxide will then form a precipitate, and come out of solution.
REACTING TWO COMPOUNDS
TO FORM A PRECIPITATE
INTRODUCTION: