Metals and Non-metals Class 10th Important Questions with Answers Science

Here are examples of metals that fit each of the given criteria:

(i) Metal that is a liquid at room temperature: Mercury (Hg)
– Mercury is the only metal that is liquid at room temperature (about 25°C).

(ii) Metal that can be easily cut with a knife: Sodium (Na)
– Sodium is a soft metal and can be easily cut with a knife. (Potassium is another similar example.)

(iii) Metal that is the best conductor of heat: Silver (Ag)
– Silver is the best conductor of heat among all metals.

(iv) Metal that is a poor conductor of heat: Lead (Pb)
– Lead is a metal but is a poor conductor of heat compared to most other metals.

Malleable

• A material is malleable if it can be hammered or rolled into thin sheets without breaking.
• This property shows the ability of a metal to withstand compression.
• Example: Gold and aluminium are highly malleable metals.

Ductile

• A material is ductile if it can be drawn into thin wires without breaking.
• This property shows the ability of a metal to stretch without breaking under tension.
• Example: Copper and silver are highly ductile metals.

Sodium is a very reactive metal. It reacts quickly and dangerously with air and water.

Reaction with water:  When sodium comes in contact with water, it reacts violently. This reaction produces sodium hydroxide (NaOH), hydrogen gas (H₂), and a lot of heat. The heat can ignite the hydrogen gas, which may cause fire.

Chemical equation:
2Na + 2H₂O → 2NaOH + H₂ (gas) + heat

Reaction with air:  Sodium also reacts with oxygen in the air and forms sodium oxide (Na₂O), which appears as a white layer on the metal.

Chemical equation:
4Na + O₂ → 2Na₂O

To prevent these dangerous reactions, sodium is stored in kerosene oil.

Kerosene does not react with sodium and protects it by blocking contact with air and water.

Conclusion:
Sodium is kept in kerosene oil to prevent it from reacting with air and water, which can be explosive or harmful.

1.  Reaction of iron with steam:
Iron reacts with steam to form iron(III) oxide and hydrogen gas.
Chemical equation:
3Fe + 4H₂O → Fe₃O₄ + 4H₂

2.  Reaction of calcium with water:
Calcium reacts slowly with cold water to form calcium hydroxide and hydrogen gas.
Chemical equation:
Ca + 2H₂O → Ca(OH)₂ + H₂

3.  Reaction of potassium with water:
Potassium reacts very quickly and violently with cold water. It forms potassium hydroxide and hydrogen gas. The reaction releases a lot of heat.
Chemical equation:
2K + 2H₂O → 2KOH + H₂

When dilute hydrochloric acid (HCl) is added to a reactive metal, hydrogen gas (H₂) is produced.

Chemical Reaction of Iron with Dilute Sulphuric Acid (H₂SO₄):- 

Iron reacts with dilute sulphuric acid to form iron(II) sulphate (FeSO₄) and hydrogen gas (H₂).

Chemical equation:
Fe + H₂SO₄ → FeSO₄ + H₂↑

When zinc is added to a solution of iron(II) sulphate (FeSO₄), the following observations and reaction occur:

Observation:

• The green color of the iron(II) sulphate solution fades.
• A grey deposit of iron forms on the zinc metal.

This happens because zinc is more reactive than iron, so it displaces iron from its salt solution.

Chemical Reaction:
Zinc + Iron(II) sulphate → Zinc sulphate + Iron

Chemical equation:
Zn + FeSO₄ → ZnSO₄ + Fe

Electron-dot structures show the valence electrons (outermost electrons) of an element as dots around the chemical symbol.

1. Sodium (Na)
Atomic number: 11
Electronic configuration: 2, 8, 1 (1 valence electron)
Electron-dot structure:
Na·

2. Oxygen (O)
Atomic number: 8
Electronic configuration: 2, 6 (6 valence electrons)
Electron-dot structure:
··
·O·
··
(6 dots are placed around the O symbol to represent 6 valence electrons)

3. Magnesium (Mg)
Atomic number: 12
Electronic configuration: 2, 8, 2 (2 valence electrons)
Electron-dot structure:
·Mg·

These compounds are formed by ionic bonding, where metals transfer electrons to non-metals.

Formation of Sodium Oxide (Na₂O)

Sodium (Na) has 1 electron in its outer shell
Oxygen (O) has 6 electrons in its outer shell and needs 2 electrons to complete its octet.
So:
2 sodium atoms each give 1 electron (total 2 electrons).
1 oxygen atom accepts those 2 electrons.
Electron transfer:
Na → Na⁺ + e⁻
O + 2e⁻ → O²⁻

Ionic compound formed:
2Na⁺ + O²⁻ → Na₂O

Formation of Magnesium Oxide (MgO)

Magnesium (Mg) has 2 electrons in its outer shell.
Oxygen (O) needs 2 electrons to complete its octet.
So:
1 magnesium atom gives 2 electrons.
1 oxygen atom accepts 2 electrons.
Electron transfer:
Mg → Mg²⁺ + 2e⁻
O + 2e⁻ → O²⁻

Ionic compound formed:
Mg²⁺ + O²⁻ → MgO

Ionic compounds have high melting points because the forces of attraction between the oppositely charged ions are very strong.

• Ionic compounds are made of positive and negative ions.
• These ions are held together by strong forces of attraction.
• A lot of heat is needed to break these bonds.
• That’s why ionic compounds have high melting points.

Examples of ionic compounds with high melting points:

• Sodium chloride (NaCl)
• Magnesium oxide (MgO)

Mineral: - A naturally occurring substance found in the earth that has a definite chemical composition. Example: Iron, gold, salt.

Ore:-  A type of mineral from which we can extract a metal easily and profitably. Example: Bauxite is an ore of aluminium.

Gangue:- The unwanted materials (like sand, mud, etc.) that are mixed with the ore. These are removed during the process of extracting the metal.

Some metals are very unreactive, which means they do not easily react with air, water, or other substances. Because of this, they are found in nature in their free or native state, meaning in pure form, not combined with other elements.  Examples:

1. Gold (Au) :- 
   1. Gold is a highly unreactive metal.
   2. It does not react with air or moisture, so it is found in the earth as shiny yellow metal lumps or nuggets.
   3. That's why we often find pure gold in riverbeds or underground rocks.
2. Platinum (Pt) :- 
   1. Platinum is also very unreactive and does not corrode or tarnish.
   2. It is found in its natural state, often mixed with other precious metals, but not combined chemically.
   3. It is rare and valuable, used in jewellery and scientific instruments.

The chemical process used for obtaining a metal from its oxide is called Reduction. In this process, oxygen is removed from the metal oxide to get the pure metal.

Example:

When iron oxide (Fe₂O₃) is heated with carbon (C), iron metal is obtained:

Fe₂O₃ + 3C → 2Fe + 3CO

Here, carbon takes away the oxygen from iron oxide, and iron is left behind.

So, reduction is the process used to extract metals from their oxides.

Metals that do not corrode easily are called less reactive or noble metals. These metals do not react easily with air, water, or acids.

Examples:

• Gold (Au)
• Platinum (Pt)
• Silver (Ag) (corrodes very slowly)
• Aluminium (Al) (forms a protective oxide layer that prevents further corrosion)

Why they don’t corrode easily:

Gold and platinum are very unreactive, so they stay shiny and do not rust or tarnish. Aluminium forms a thin layer of aluminium oxide on its surface, which protects it from further corrosion.

Alloys are mixtures of two or more metals, or a metal and a non-metal. They are made to improve the properties of metals, like making them stronger, harder, or resistant to rust.

Examples:

• Brass = Copper + Zinc
• Bronze = Copper + Tin
• Steel = Iron + Carbon
• Stainless Steel = Iron + Chromium + Nickel
• Solder = Lead + Tin

Why are alloys made?

• To make metals stronger
• To prevent rusting (corrosion)
• To improve hardness or appearance

To determine if a displacement reaction will occur, we use the reactivity series of metals. In a displacement reaction, a more reactive metal displaces a less reactive metal from its salt solution.

Reactivity series :--  Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > Hydrogen (H) > Copper (Cu) > Mercury (Hg) > Silver (Ag) > Gold (Au)

Now, let’s check each pair:

1. NaCl solution and copper metal :- Copper is less reactive than sodium. So, copper cannot displace sodium from NaCl. No reaction.
2. MgCl₂ solution and aluminium metal :-- Aluminium is more reactive than magnesium. So, aluminium can displace magnesium from MgCl₂. So Displacement reaction occurs.
3. FeSO₄ solution and silver metal :-- Silver is less reactive than iron. So, silver cannot displace iron from FeSO₄. No reaction.
4. AgNO₃ solution and copper metal :-- Copper is more reactive than silver. So, copper can displace silver from AgNO₃. Displacement reaction occurs.

Rusting of iron happens when iron comes in contact with oxygen and moisture (water) from the air. To prevent rusting, we need to stop air and water from reaching the iron surface.

Let’s look at each method:

(a) Applying grease –Grease forms a layer that prevents air and moisture from touching the iron.
(b) Applying paint –Paint also acts as a barrier and protects the iron from rusting.
(c) Applying a coating of zinc –This method is called galvanization. Zinc protects the iron by forming a coating and also by sacrificing itself (zinc reacts before iron does).

All these methods help in preventing rusting.

So correct answer: - (d) All of the above

(a) Calcium : - Calcium reacts with oxygen to form calcium oxide (CaO). Calcium oxide has a high melting point. It is soluble in water, forming calcium hydroxide. This matches both conditions.

(b) Carbon :- Carbon forms carbon dioxide or carbon monoxide when it reacts with oxygen. These are gases, not solids with high melting points. Does not match.

(c) Silicon :- Silicon forms silicon dioxide (SiO₂), which has a high melting point. But it is not soluble in water. Does not match.

(d) Iron :-  Iron forms iron oxides when it reacts with oxygen. They have high melting points but are not soluble in water. Does not match.

Correct answer:
(a) Calcium

The correct answer is: (c) zinc is more reactive than tin.

Because, food cans are coated with tin and not zinc primarily because zinc is more reactive than tin. If zinc were used, it could react with the acids present in food, potentially leading to contamination or spoilage. Tin, being less reactive, is safer and more stable in contact with food, making it the preferred coating material.

(a) How could you use a hammer, a battery, a bulb, wires and a switch to distinguish between samples of metals and non-metals?

• Hammer Test (Malleability Test):
  • Hit the sample gently with the hammer.
  • If the sample flattens or bends without breaking, it is likely a metal (metals are malleable).
  • If the sample breaks or shatters, it is likely a non-metal (non-metals are brittle).
• Electrical Conductivity Test:
  • Make a simple circuit using the battery, bulb, wires, and switch.
  • Place the sample between two wire ends in the circuit.
  • Turn on the switch and observe the bulb.
  • If the bulb lights up, the sample conducts electricity and is likely a metal.
  • If the bulb does not light up, the sample does not conduct electricity and is likely a non-metal.

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals:

• These tests are useful because they are based on basic properties:
  • Metals are usually malleable and conduct electricity.
  • Non-metals are usually brittle and poor conductors of electricity.
• The tests are simple and can be done easily in a classroom or lab.
• However, there are some limitations:
  • Some non-metals like graphite can conduct electricity.
  • Some metals like mercury are liquid and cannot be hammered.
  • Metalloids may not clearly behave like metals or non-metals.
  • Surface coatings or rust on metals can affect the results.

Amphoteric oxides are oxides that react with both acids and bases to form salt and water. This means they show both acidic and basic behavior.

Examples of amphoteric oxides:

1. Aluminum oxide (Al₂O₃)
2. Zinc oxide (ZnO)

Metals that will displace hydrogen from dilute acids:

These are more reactive than hydrogen and can replace it in a chemical reaction.

1. Zinc (Zn)
2. Iron (Fe)

Example reaction:
Zn + 2HCl → ZnCl₂ + H₂↑

Metals that will not displace hydrogen from dilute acids:

These are less reactive than hydrogen and do not react with dilute acids to release hydrogen gas.

1. Copper (Cu)
2. Silver (Ag)

These metals do not react with dilute hydrochloric acid or sulfuric acid under normal condition

In the electrolytic refining of a metal M:

1. Anode: Impure metal M (this is the metal you want to purify)
2. Cathode: Pure metal M (a thin strip of the same metal)
3. Electrolyte: A solution of a salt of metal M (like M nitrate or M sulfate)

What happens during refining:

• The impure metal at the anode dissolves into the solution.
• Pure metal gets deposited on the cathode.
• Impurities either stay in the solution or settle down as anode mud.

Example with copper:

• Anode: Impure copper
• Cathode: Pure copper
• Electrolyte: Copper sulfate (CuSO₄) solution

Two simple ways to prevent the rusting of iron:

1. Painting or Coating with Oil/Grease:- This creates a barrier that prevents air and moisture from reaching the iron surface.
2. Galvanization: - This means coating the iron with a thin layer of zinc. Zinc protects the iron by preventing contact with air and water and also acts as a sacrificial metal.

When non-metals combine with oxygen, they form acidic oxides. 

Example:- 
Carbon + Oxygen    ---------->    Carbon dioxide (CO₂)
CO₂ is an acidic oxide because it dissolves in water to form an acid:
CO₂ + H₂O → H₂CO₃ (carbonic acid)

So, non-metals form acidic oxides when they react with oxygen.

(a) Why are platinum, gold, and silver used to make jewellery?

Because they are lustrous, shiny, and do not react easily with air or water. So, they do not rust or tarnish and keep their shine for a long time.

(b) Why are sodium, potassium, and lithium stored under oil?

Because these metals react very quickly with air and water, sometimes catching fire. Storing them under oil stops them from coming in contact with air and moisture.

(c) Why is aluminium, a highly reactive metal, used to make cooking utensils?

Because aluminium forms a thin, tough layer of oxide on its surface which protects it from further reaction. This makes it safe and durable for cooking.

(d) Why are carbonate and sulphide ores usually converted into oxides during extraction?

Because oxides are easier to reduce to the metal in the extraction process, usually by heating with carbon or carbon monoxide.

Lemon or tamarind juice is sour because it contains citric acid or tartaric acid. These acids react with the tarnish on copper vessels, which is mainly copper oxide or copper carbonate.
The acids react with the tarnish, dissolving it and turning it into soluble compounds that can be washed away. This makes the copper vessel clean and shiny again. 

So, the sour substances help remove the layer of tarnish by reacting with it chemically.

Simple difference between metals and non-metals based on their chemical properties:

• Reaction with oxygen: - Metals usually form basic or amphoteric oxides. Non-metals form acidic oxides.
• Reaction with acids:- Metals react with dilute acids to produce hydrogen gas. Non-metals usually do not react with acids.
• Reaction with water:- Some metals like sodium and potassium react with water to form hydroxides and hydrogen gas. Non-metals generally do not react with water.
• Electropositivity:- Metals tend to lose electrons and form positive ions. Non-metals tend to gain or share electrons.
• Reaction with non-metals:- Metals generally form ionic compounds with non-metals. Non-metals usually form covalent compounds with each other.

The man used a strong acid (like aqua regia or a mixture of strong acids) to clean the gold bangles. This solution can dissolve impurities and dirt on the surface, making the bangles sparkle like new.

However, if the bangles were not pure gold but gold-plated or alloyed with cheaper metals, the acid would have dissolved some of the metal along with the impurities, reducing their weight drastically.

So, the solution used was an acid that can dissolve metals, which cleaned the bangles but also dissolved some of the metal, making them lighter.

This is why the bangles shined but lost weight.

Why copper is used to make hot water tanks and not steel:

Resistance to rust and corrosion:
Steel, which contains iron, easily reacts with water and oxygen to form rust (iron oxide). Rust weakens the steel, making it less durable and unsafe for storing water. Copper, on the other hand, is much more resistant to corrosion and does not rust easily. This means copper tanks last longer and stay safe for water storage.

Better heat conduction:
Copper is an excellent conductor of heat. This means it can quickly and evenly transfer heat to the water inside the tank. This helps in heating the water faster and saves energy. Steel is not as good a conductor, so it heats water more slowly.

Non-toxic and safe:
Copper does not release harmful substances into water, making it safe for storing hot water used for household purposes.

Maintenance and durability:
Because copper does not rust and conducts heat well, copper tanks require less maintenance and have a longer life compared to steel tanks, which may need frequent repairs due to rust.