Mention the various visible changes that occur when a piece of calcium is dropped
into a test-tube containing cold water and a coil of magnesium is heated in a current
of
steam. Write equation for each reaction. [4]
b. i) Give two examples of reactions in which water acts as a catalyst. [2, 1]
ii) What is solubility curve?
c. Explain the terms deliquescence, efflorescence and supersaturated solution.
Answers
Answer:
Calcium is a silvery-white metal; it is relatively soft, but much harder than sodium metal. Calcium is a member of the alkaline-earth metals (Group II on the periodic table); these metals react vigorously with water, although not as violently as the Group I metals such as sodium or potassium:
Ca(s) + 2H2O(l) ——> Ca(OH)2(aq) + H2(g)
In the following demonstration, a chunk of calcium metal is dropped into a beaker of distilled water. After a second or so, the calcium metal begins to bubble vigorously as it reacts with the water, producing hydrogen gas, and a cloudy white precipitate of calcium hydroxide. The presence of the hydroxide is demonstrated by the addition of a few drops of phenolphthalein indicator, which turns the solution pink, indicating that the solution is basic.