Metals and Non-Metals: Chemical Properties of Metals

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Medium Complexity (Application & Explanation)

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Q1. Explain how different metals react with cold water, hot water, and steam with suitable examples and equations.

Answer:
Metals show different reactivities with water depending on their position in the reactivity series. Potassium (K) and Sodium (Na) react explosively with cold water, producing their hydroxides and hydrogen gas:

$$2K + 2H_2O \rightarrow 2KOH + H_2 \uparrow$$

Calcium (Ca) reacts readily but less violently:

$$Ca + 2H_2O \rightarrow Ca(OH)\_2 + H_2 \uparrow$$

Magnesium (Mg) reacts slowly with cold water, but rapidly with hot water or steam, producing magnesium hydroxide and then oxide:

$$Mg + 2H_2O \xrightarrow{hot} Mg(OH)\_2 + H_2 \uparrow$$ $$Mg + H_2O (\text{steam}) \rightarrow MgO + H_2 \uparrow$$

Zinc (Zn) and Iron (Fe) don’t react with cold/hot water, only with steam:

$$Zn + H_2O (\text{steam}) \rightarrow ZnO + H_2 \uparrow$$ $$3Fe + 4H_2O (\text{steam}) \rightarrow Fe_3O_4 + 4H_2 \uparrow$$

Less reactive metals (Cu, Ag, Au) don't react with water at all.

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Q2. Describe the formation and nature of metal oxides when metals react with oxygen. Give different examples with equations.

Answer:
When metals react with oxygen, they form metal oxides. The reactivity determines the speed of this reaction. Sodium (Na) and Potassium (K) react very rapidly:

$$4Na + O_2 \rightarrow 2Na_2O$$

Magnesium (Mg) burns with a bright flame:

$$2Mg + O_2 \rightarrow 2MgO$$

Aluminium (Al) forms a protective oxide layer:

$$4Al + 3O_2 \rightarrow 2Al_2O_3$$

Iron (Fe) forms different oxides like magnetite:

$$3Fe + 2O_2 \rightarrow Fe_3O_4$$

Copper (Cu) forms a black oxide only when heated:

$$2Cu + O_2 \rightarrow 2CuO$$

Some metals (Au, Pt) do not react with oxygen. Most metal oxides are basic, some (like Al$_2$O$_3$ and ZnO) are amphoteric.

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Q3. What happens when a metal reacts with a dilute acid? Explain using at least two specific examples with equations.

Answer:
Most metals react with dilute acids to produce a salt and hydrogen gas. For example, when Zinc (Zn) reacts with hydrochloric acid:

$$Zn + 2HCl \rightarrow ZnCl_2 + H_2 \uparrow$$

Similarly, Magnesium (Mg) reacts with sulphuric acid:

$$Mg + H_2SO_4 \rightarrow MgSO_4 + H_2 \uparrow$$

The reaction is usually faster with more reactive metals. However, less reactive metals like Copper (Cu), Silver (Ag), and Gold (Au) do not react with dilute acids, as they are below hydrogen in the reactivity series.

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Q4. Explain displacement reactions among metals using the activity series. Give two examples with chemical equations.

Answer:
A more reactive metal can displace a less reactive metal from its salt solution. This is called a displacement reaction, explained using the activity series. For example, when Zinc (Zn) is put into Copper Sulphate (CuSO$_4$) solution:

$$Zn (s) + CuSO_4 (aq) \rightarrow ZnSO_4 (aq) + Cu (s)$$

Here, zinc is more reactive and so it displaces copper. Similarly, Iron (Fe) displaces copper:

$$Fe (s) + CuSO_4 (aq) \rightarrow FeSO_4 (aq) + Cu (s)$$

But, copper placed in iron sulphate solution will not react because copper is less reactive.

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Q5. Metals like Aluminium, despite being reactive, don’t get corroded easily. Explain why with a chemical reason.

Answer:
Although Aluminium (Al) is a reactive metal, it does not corrode easily. This is because when aluminium is exposed to air, it quickly forms a thin, tough coating of aluminium oxide (Al$_2$O$_3$):

$$4Al + 3O_2 \rightarrow 2Al_2O_3$$

This oxide layer sticks to the metal and prevents further oxygen or moisture from reacting with the underlying aluminium. Therefore, the inside remains protected. This process is a form of passivation—the protective oxide layer acts as a barrier, preventing corrosion.

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High Complexity (Analysis & Scenario-Based)

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Q6. Scenario: You dip an iron nail in copper sulphate solution and observe it after some time. What changes would you see? Write the relevant equation and explain the reason.

Answer:
When an iron nail is placed in copper sulphate solution, after a while, a brown coating forms on the nail and the blue color of the solution fades.
The chemical reaction is:

$$Fe (s) + CuSO_4 (aq) \rightarrow FeSO_4 (aq) + Cu (s)$$

Iron is more reactive than copper, so it displaces copper from the solution. The brown deposit is copper metal, while the solution turns light green due to iron(II) sulphate. This demonstrates the concept of displacement reactions based on activity series.

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Q7. Imagine a scenario where you have three metals: Magnesium, Copper, and Zinc. Predict and explain what would happen if each metal is placed in the other metals' salt solutions.

Answer:
Using the reactivity series:

• Magnesium (Mg) is more reactive than zinc (Zn) or copper (Cu).
• Zinc is more reactive than copper.

So,

1. Magnesium in ZnSO$_4$ or CuSO$_4$: Magnesium will displace both zinc and copper.

   • With CuSO$_4$: $$Mg + CuSO_4 \rightarrow MgSO_4 + Cu$$
   • With ZnSO$_4$: $$Mg + ZnSO_4 \rightarrow MgSO_4 + Zn$$

2. Zinc in CuSO$_4$: Zinc will displace copper.

   $$Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$$

   Zinc in MgSO$_4$ will not react, since magnesium is more reactive.

3. Copper in MgSO$_4$ or ZnSO$_4$: Copper won’t react with either; no displacement.

Thus, more reactive metals always displace less reactive ones from their salts.

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Q8. Analyse why copper utensils do not react with dilute hydrochloric acid but react with oxygen when heated.

Answer:
Copper (Cu) is less reactive than hydrogen in the activity series. When placed in dilute hydrochloric acid (HCl), copper cannot displace hydrogen, so no reaction occurs.
However, when copper is heated in oxygen, it combines to form copper(II) oxide (CuO):

$$2Cu + O_2 \rightarrow 2CuO$$

This is because copper, though not very reactive, can react with oxygen when supplied with enough energy (heat). So, copper utensils stay safe in acids but turn black when heated due to oxide formation.

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Q9. How does the reactivity of a metal influence the products formed when it reacts with water or acids? Cite examples from both reactions.

Answer:
The higher the reactivity of a metal, the faster it reacts and the more vigorous are the reactions.

• With water: Very reactive metals (Na, K) react quickly and form metal hydroxides and hydrogen.
  For potassium: $$2K + 2H_2O \rightarrow 2KOH + H_2 \uparrow$$ Less reactive metals (Fe, Zn) react only with steam, not cold water, giving metal oxides and hydrogen.
  For iron: $$3Fe + 4H_2O (\text{steam}) \rightarrow Fe_3O_4 + 4H_2 \uparrow$$
• With acids: Highly reactive metals react violently; less reactive metals react slowly or not at all. For magnesium: $$Mg + 2HCl \rightarrow MgCl_2 + H_2 \uparrow$$ But metals below hydrogen (Cu, Ag) do not react with dilute acids. So, product formation depends on metal’s position in the reactivity series.

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Q10. Design an activity and explain how you would experimentally prove that hydrogen gas is released when a metal reacts with an acid.

Answer:
Activity Setup:

• Take a test tube. Add a small amount of dilute hydrochloric acid.
• Drop pieces of zinc or magnesium into the acid.
• Immediately, observe bubbling; a gas forms (hydrogen).
• To confirm, bring a burning matchstick or candle near the mouth of the test tube.

Observation and Explanation:

• The gas produces a ‘pop’ sound. This is the characteristic test for hydrogen gas, as hydrogen is combustible.
• Reaction for zinc: $$Zn + 2HCl \rightarrow ZnCl_2 + H_2 \uparrow$$
• This proves that when a reactive metal reacts with an acid, hydrogen gas is produced.
• The experiment can also help compare the speed of reaction among different metals.

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