Key Reactions and Examples of Metals with Water
Not every metal reacts with water in a similar ratio. Various metals react with water in distinct ways. Metals like potassium and sodium interact with water so violently that if left out in the open, they will catch fire. Therefore, they are kept submerged in kerosene oil to safeguard them and stop unintentional fires.
Metals like magnesium, aluminium, zinc, lead, etc. have a thin oxide layer covering their surfaces at room temperature. The shielding oxide layer stops the metal from oxidising any further. Hence, this article on what happens when metal reacts with water gives more in depth information on how metals react with water with certain examples.
Reaction of Metal with Water
Hydrogen gas and metal oxides are produced when metal reacts with water. Metal hydroxide is created when soluble metal oxides are dissolved in water. However, not all metals react with water. The basic expression for this reaction is given below:
\[Metal + Water \to Metal\;Oxide + Hydrogen\]
Which Metals React Readily with Cold Water?
Sodium (Na), Potassium (K), and Calcium (Ca) are the metal which reacts readily with cold water. The reactions on how metals react with water is explained below.
Which Metals React Readily with Hot Water?
Magnesium metal does not react with cold water however it reacts readily with hot water. Its reactivity and formation was explained in detail in the following section.
Reaction of Sodium and Potassium with Water
Cold water and metals, like sodium and potassium, react vigorously. Na and K metals react with cold water and produce sodium hydroxide (NaOH) and potassium hydroxide (KOH).
\[2K\left( s \right) + 2{H_2}O\left( l \right) \to 2KOH\left( {aq} \right) + {H_2}\left( g \right) + Heat\;Energy\]
\[2Na\left( s \right) + 2{H_2}O\left( l \right) \to 2NaOH\left( {aq} \right) + {H_2}\left( g \right) + Heat\;Energy\]
Reaction of Calcium (Ca) Metal with Water
Calcium reacts less violently with cold water compared to other metals. Ca reacts with cold water and produces calcium hydroxide Ca(OH)2.
\[Ca\left( s \right) + 2{H_2}O\left( l \right) \to Ca{(OH)_2}\left( {aq} \right) + {H_2}\left( g \right)\]
Reaction of Magnesium (Mg) Metal with Water
Hot water causes Mg to react violently. Mg metal reacts with hot water to produce magnesium hydroxide (MgOH).
\[Mg\left( s \right) + 2{H_2}O\left( l \right) \to Mg{\left( {OH} \right)_2}\left( {aq} \right) + {H_2}\left( g \right)\]
Reaction of Aluminium (Al) Metal with Water
Aluminium does not react with hot and cold water. Steam, though, causes it to react. Al reacts with steam to produce aluminium oxide (Al2O3).
\[2Al\left( s \right) + 3{H_2}O\left( g \right) \to A{l_2}{O_3}\left( s \right) + 3{H_2}\left( g \right)\]
Reaction of Iron (Fe) Metal with Water
Iron also does not react with both cold and hot water. The slow and gradual reaction of iron with cold water takes a while to become noticeable. However, when Fe reacts with steam iron oxide (Fe3O4) is produced.
\[3Fe\left( s \right) + 4{H_2}O\left( g \right) \to F{e_3}{O_4}\left( s \right) + 4{H_2}\left( g \right)\]
Reaction of Zinc (Zn) Metal with Water
Cold water does not cause zinc to react. However, when steam is applied to Zn metal, hydrogen gas and zinc oxide (ZnO) is produced.
\[Zn\left( s \right) + {H_2}O\left( g \right) \to ZnO\left( s \right) + {H_2}\left( g \right)\]
Interesting Facts
As calcium hydroxide is only moderately soluble in water, when the solution is saturated, solid calcium hydroxide begins to emerge, and the solution begins to turn milky.
In response to the hydrogen gas bubbles that are stuck to the metal's surface as a result of the reaction, calcium and magnesium begin to float.
The standard equipment that is utilised to react calcium with water and capture the gas, the same apparatus cannot be used for sodium and potassium since their reactions are very vigorous compared to calcium.
Key Features to Remember
Metal oxide and hydrogen gas is created when a metal and water reacts together.
Metal + water = metal oxide + hydrogen is the fundamental equation for the metal reaction with water.
Cold water and the metals sodium, potassium, and calcium quickly react to form hydroxides.
Magnesium reacts with hot water rather than cold water to form hydroxide.
Oxides are produced when zinc, aluminium, and steam react. Cold water and iron react very slowly and may take days to complete. However, Iron oxide is created when iron combines with steam.
FAQs on What Happens When Metals React with Water?
1. What are the general products formed when a metal reacts with water?
When a metal reacts with water, the primary products are a metal oxide and hydrogen gas. However, if the metal oxide formed is soluble in water, it further dissolves to form a metal hydroxide. The general chemical equations are:
- Metal + Water → Metal Oxide + Hydrogen Gas
- Metal Oxide + Water → Metal Hydroxide
2. Which metals react vigorously with cold water, and what are the key observations?
Highly reactive metals like potassium (K) and sodium (Na) react vigorously and exothermically with cold water. The key observations are:
- The reaction is violent and produces a large amount of heat, making it an exothermic reaction.
- Hydrogen gas is evolved immediately, which can be seen as effervescence.
- In the case of sodium and potassium, the heat produced is so intense that the evolved hydrogen gas catches fire.
- For example, the reaction with potassium is: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + heat energy.
3. How does the reaction of magnesium with water differ from that of sodium?
Unlike sodium, magnesium (Mg) does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen gas. A key observation is that the piece of magnesium metal starts to float on the water surface. This happens because the bubbles of hydrogen gas produced during the reaction stick to its surface, reducing its overall density.
4. What is the difference in reaction when metals like aluminium, iron, and zinc react with steam?
Metals like aluminium (Al), zinc (Zn), and iron (Fe) are less reactive and do not react with either cold or hot water. They react only with steam (gaseous water) to form a metal oxide and hydrogen gas. Unlike more reactive metals that form hydroxides, these metals form oxides because the hydroxides are unstable at high temperatures. For example, iron reacts with steam to form iron(II,III) oxide:
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g).
5. Which common metals do not react with water at all, and why?
Metals that are placed below hydrogen in the reactivity series do not react with water in any form (cold, hot, or steam). This is because they are less reactive than hydrogen and cannot displace it from water molecules. Common examples of such metals include lead (Pb), copper (Cu), silver (Ag), and gold (Au).
6. Why do different metals like potassium, magnesium, and iron show varying reactivity with water?
The varying reactivity of metals with water is determined by their position in the reactivity series. This series arranges metals based on their ability to lose electrons.
- Potassium (K) is at the top, meaning it loses electrons very easily and thus reacts explosively with cold water.
- Magnesium (Mg) is lower down, requiring more energy (from hot water) to react.
- Iron (Fe) is even less reactive and needs a significant amount of energy, provided by steam, to react.
7. Under what conditions do metals form metal hydroxides versus metal oxides when reacting with water?
The product formed depends on the metal's reactivity and the reaction conditions:
- Metal Hydroxides are formed when highly reactive metals (like sodium, potassium, calcium) react with cold or hot water. Their resulting oxides are soluble in water and readily form hydroxides.
- Metal Oxides are formed when less reactive metals (like aluminium, zinc, iron) react with steam. The high temperature of the steam prevents the formation of stable metal hydroxides, resulting in the formation of the metal oxide instead.
8. Why do calcium and magnesium start floating when they react with water?
When calcium (with cold water) and magnesium (with hot water) react, they produce hydrogen gas. The bubbles of this gas get stuck to the surface of the metal pieces. This accumulation of gas bubbles makes the effective density of the metal less than that of water, causing it to become buoyant and float to the surface. It is a physical phenomenon driven by a chemical reaction.
