Question

Why does calcium float in water?

Answer 1

Metals when reacted with water ,it produces metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it, then it is further form metal hydroxide. But all metals do not react with water violently, some react with cold water vigorously while some react with hot water violently.

Complete step by step answer:
Calcium is the s-block element of the 2nd group and 4th period. It is having atomic number 20 and is alkaline in nature. Calcium is the fifth most abundant element found in the earth's crust .
The reaction between water and calcium is less violent. Therefore the heat evolved is not sufficient for the hydrogen to catch fire. Thus the calcium starts floating because the bubbles of hydrogen gas formed get stuck to the surface of the metal.
Additional information: Calcium is full gray , silver with a pale yellow tint. The most common calcium compound on earth is calcium carbonate that is found in limestone. It is present in all dairy products like cheese, milk,yogurt that is beneficial for bones.
Calcium is highly reactive in nature. Thus they are never found in a free state. Thus it is extracted by the help of electrolysis of its molten ore.
Calcium is showing a highly exothermic reaction when calcium oxide reacts with water to produce slaked lime(calcium hydroxide) which is used in white wash.

Note:
Magnesium does not react with cold water. When magnesium reacts with hot water, it form Magnesium hydroxide and hydrogen. It also starts floating in water due to the bubbles of hydrogen gas sticking to its surface.
Some metals such as lead,copper,silver and gold do not react with water.