Metals and Non-metals · Lesson 4 of 13
What Happens When Metals React With Water?
“Some metals explode into action with cold water while others demand steam or refuse entirely.”
• Compare reactions of metals with cold water, hot water and steam. • Write balanced equations for potassium, sodium, calcium, aluminium and iron reacting with water or steam. • Explain why evolved hydrogen may catch fire in very vigorous reactions. • Explain why calcium and magnesium may float during reaction with water. • Use water reactivity to compare metals qualitatively.
Water does not react with every metal in the same way. Some metals react violently with cold water, some need hot water, some react only with steam and some do not react with water at all.
What Happens When Metals React With Water?
Potassium And Sodium
Potassium and sodium react violently with cold water. The reactions are strongly exothermic and the evolved hydrogen may catch fire.
Calcium
Calcium reacts less violently with cold water to form calcium hydroxide and hydrogen. Hydrogen bubbles stick to the metal surface, so the calcium can begin to float.
Magnesium
Magnesium does not react appreciably with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen, and hydrogen bubbles can make it float.
Aluminium, Zinc And Iron
These metals do not react with cold or hot water under the described conditions, but they react with steam to form metal oxides and hydrogen.
Lead, Copper, Silver And Gold
Lead, copper, silver and gold do not react with water. Their lack of reaction indicates lower reactivity than metals such as sodium or calcium.
| Metal Or Group | Condition | Observation |
|---|---|---|
| Potassium, sodium | Cold water | Violent; hydrogen may ignite |
| Calcium | Cold water | Less violent; may float |
| Magnesium | Hot water | Hydrogen forms; may float |
| Aluminium, zinc, iron | Steam | Metal oxide and hydrogen form |
| Lead, copper, silver, gold | No reaction | No reaction with water |
Problem
Metal X reacts with steam but not with cold or hot water. Metal Y reacts violently with cold water. Which is more reactive?
- 1.Y reacts under milder conditions.
- 2.X requires steam.
- 3.Therefore Y is more reactive in this comparison.
Quiz
Which metals react violently with cold water?
Why can calcium float during reaction with water?
Which metal reacts with hot water but not appreciably with cold water?
Which set reacts with steam?
What gas is commonly released in these metal-water reactions?
Practice Problems
- Write balanced equations for potassium, sodium and calcium reacting with water.
- Explain why hydrogen may ignite during the sodium and potassium reactions.
- Explain why calcium and magnesium can float while reacting with water.
- Write balanced equations for aluminium and iron reacting with steam.
- Arrange these behaviours from greater to lower reactivity: violent cold-water reaction; hot-water reaction; steam reaction; no reaction.
- Compare magnesium and iron using their behaviour toward water and steam.
Key Takeaways
• Metal-water reactions vary greatly with reactivity. • Potassium and sodium react violently with cold water and can ignite hydrogen. • Calcium reacts with cold water, while magnesium reacts with hot water. • Aluminium, zinc and iron react with steam to form metal oxides and hydrogen. • Lead, copper, silver and gold do not react with water under the conditions described.