Which metal reacts vigorously with cold water?

The metal that reacts vigorously with cold water is potassium.

Explanation:

When a metal reacts with water, it can produce metal hydroxide and hydrogen gas. The reactivity of a metal with water depends on the metal's position in the reactivity series. Metals at the top of the reactivity series are more reactive and tend to react more vigorously with water.

Reactivity series:
1. Potassium
2. Sodium
3. Calcium
4. Magnesium
5. Aluminium
6. Zinc
7. Iron
8. Lead
9. Copper
10. Silver
11. Gold

Potassium is the most reactive metal in the reactivity series. It is located at the top of the series, indicating that it has a strong tendency to lose electrons and form positive ions. This makes it highly reactive with water.

Reaction of potassium with water:

When potassium reacts with water, it produces potassium hydroxide (KOH) and hydrogen gas (H2).

2K + 2H2O → 2KOH + H2

The reaction is exothermic, which means it releases heat. The heat generated by the reaction ignites the hydrogen gas, causing it to burn with a characteristic lilac flame. The reaction is also highly exothermic and can be violent, with the potassium metal moving rapidly across the surface of the water.

Precautions:

When handling potassium or other highly reactive metals, it is essential to follow safety precautions due to their reactive nature. Some precautions include:

1. Wearing safety goggles and gloves to protect the eyes and skin from potential splashes or contact with reactive substances.
2. Working in a well-ventilated area to prevent the accumulation of potentially harmful gases.
3. Using appropriate equipment, such as tongs or spatulas, to handle the metal and avoid direct contact with the skin.
4. Working on a heat-resistant surface to prevent any accidental fires due to the exothermic reaction.
5. Ensuring proper disposal of any waste or leftover materials to prevent environmental contamination.

Conclusion:

In conclusion, potassium is the metal that reacts vigorously with cold water. Its high position in the reactivity series and strong tendency to lose electrons make it highly reactive, resulting in a violent reaction with water. It is crucial to handle potassium and other highly reactive metals with caution and follow appropriate safety measures.