5. What is the nature of a solution of calcium hydroxide? How will you confirm it?
Answers
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed, or slaked with water.
Identifying calcium hydroxide requires two tests. The first one measures the pH (acidity) of the calcium hydroxide solution to ensure it is basic. The second test, using a dilute solution of sulphuric acid, determines the presence of calcium ions.
Pour about 5 milliliters of the solution to be tested into the beaker.
Dip the strip of the pH paper strip into the solution and then take it out. The pH paper will change its color.
Compare the color of the paper with the scale enclosed with the pH paper to assign the pH of the solution. A basic pH value such as 10 to 11 is indicative for calcium hydroxide.
Fill a pipette with the sulphuric acid solution.
Add five to ten drops of the solution from the pipette to the beaker.
Observe the solution in the beaker: If a white precipitate forms, it indicates the presence of calcium ions; this reaction follows the equation Ca(OH)2 + H2SO4 = CaSO4 (precipitate) + 2H2O.