NCERT Class 10 Science Solutions: Metals and Non-metals

Question:

An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be:

A. calcium

B. carbon

C. silicon

D. iron

Concept in a Minute:

The question tests the understanding of the properties of oxides formed by different elements, specifically focusing on their melting points and solubility in water. The key concept is that metallic oxides generally have high melting points and are often soluble in water (especially oxides of Group 1 and 2 metals), while non-metallic oxides typically have lower melting points and are insoluble or react with water to form acids.

Explanation:

Let’s analyze the options:

A. Calcium (Ca) is a metal. Calcium reacts with oxygen to form calcium oxide (CaO). Calcium oxide is an ionic compound, which are known to have high melting points. Calcium oxide is also soluble in water, forming calcium hydroxide (Ca(OH)2).

B. Carbon (C) is a non-metal. Carbon reacts with oxygen to form carbon dioxide (CO2) (and carbon monoxide, CO). Carbon dioxide is a covalent compound with a very low melting point (it sublimes at -78.5 °C). CO2 dissolves in water to form carbonic acid, but the compound itself is not described as having a high melting point.

C. Silicon (Si) is a metalloid. Silicon reacts with oxygen to form silicon dioxide (SiO2). Silicon dioxide has a very high melting point (around 1700 °C). However, SiO2 is generally insoluble in water. It reacts with strong bases.

D. Iron (Fe) is a metal. Iron reacts with oxygen to form iron oxides (e.g., Fe2O3). Iron oxides have relatively high melting points. However, iron oxides are generally insoluble in water.

Comparing the options with the question’s criteria (high melting point and soluble in water), calcium oxide fits perfectly. Calcium is a Group 2 metal, and its oxide exhibits these properties.

The final answer is $\boxed{A}$.

Question:

Which of the following pairs will give displacement reactions?

A. NaCl solution and copper metal

B. MgCl 2 solution and aluminium metal

C. FeSO 4 solution and silver metal

D. AgNO 3 solution and copper metal.

Concept in a Minute:

Displacement reactions occur when a more reactive metal displaces a less reactive metal from its salt solution. Reactivity of metals is determined by their position in the reactivity series. A metal higher in the reactivity series can displace a metal lower in the series from its compound.

Explanation:

To determine which pair will give a displacement reaction, we need to consider the reactivity series of metals. The reactivity series (from most reactive to least reactive) is roughly: Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Hydrogen > Copper > Silver > Gold.

Let’s analyze each option:

A. NaCl solution and copper metal: Sodium (Na) is much more reactive than Copper (Cu). Copper cannot displace sodium from NaCl solution.

B. MgCl2 solution and aluminium metal: Magnesium (Mg) is more reactive than Aluminium (Al). Aluminium cannot displace magnesium from MgCl2 solution.

C. FeSO4 solution and silver metal: Iron (Fe) is more reactive than Silver (Ag). Silver cannot displace iron from FeSO4 solution.

D. AgNO3 solution and copper metal: Copper (Cu) is more reactive than Silver (Ag). Therefore, copper will displace silver from silver nitrate (AgNO3) solution. The reaction would be:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

Thus, the pair that will give a displacement reaction is AgNO3 solution and copper metal.

Question:

Which of the following methods is suitable for preventing an iron frying pan from rusting?

A. Applying grease

B. Applying paint

C. Applying a coating of zinc

D. all of the above.

Concept in a Minute:

Rusting is the oxidation of iron in the presence of moisture and air. To prevent rusting, we need to create a barrier that prevents iron from coming into contact with oxygen and water. Common methods involve applying protective coatings.

Explanation:

Rusting of iron occurs when it reacts with oxygen and moisture. The question asks for methods to prevent an iron frying pan from rusting. Let’s analyze the options:

A. Applying grease: Grease forms a waterproof layer on the surface of the iron, preventing moisture and air from reaching it. This effectively prevents rusting.

B. Applying paint: Paint also forms a protective barrier on the surface of the iron, isolating it from the environment. This prevents contact with oxygen and water, thus inhibiting rust formation.

C. Applying a coating of zinc: This method is known as galvanization. Zinc is more reactive than iron. If the zinc coating is scratched, the zinc will corrode sacrificially, protecting the iron from rusting. This is a very effective method for preventing rust.

D. All of the above: Since options A, B, and C are all valid and effective methods for preventing iron from rusting, this option is the most comprehensive and correct answer.

Therefore, all the listed methods are suitable for preventing an iron frying pan from rusting.

Answer: D

Question:

Food cans are coated with tin and not with zinc because ______.

A. zinc is costlier than tin

B. zinc has a higher melting point than tin

C. zinc is more reactive than tin

D. zinc is less reactive than tin

Concept in a Minute:

Reactivity series of metals, Sacrificial protection, Corrosion

Explanation:

Food cans are coated with tin to protect the iron from rusting. Iron is more reactive than tin. If the tin coating is scratched, exposing the iron, the tin will act as a sacrificial anode and corrode instead of the iron. Zinc, on the other hand, is more reactive than iron. If a zinc-coated can is scratched, the zinc will preferentially corrode, which could lead to contamination of the food with zinc and a less effective protection for the iron. Therefore, tin is preferred over zinc for coating food cans because it is less reactive than iron and provides better protection in case of minor damage to the coating.

The final answer is $\boxed{C}$.

Question:

Give reasons:

Platinum, gold and silver are used to make jewellery.

Concept in a Minute:

The question asks for reasons why platinum, gold, and silver are used to make jewelry. This requires understanding the properties of these metals that make them suitable for such applications. Key properties to consider include their appearance, malleability, ductility, and reactivity (or lack thereof).

Explanation:

Platinum, gold, and silver are used to make jewelry primarily due to a combination of their desirable physical and chemical properties:

1. Appearance: They are all lustrous, attractive metals with a beautiful sheen. Gold has a distinct yellow color, silver is a bright white, and platinum is a silvery-white metal. This aesthetic appeal is fundamental for jewelry.

2. Malleability and Ductility: These metals are highly malleable, meaning they can be hammered into very thin sheets without breaking. They are also very ductile, which means they can be drawn into thin wires. This allows jewelers to shape them into intricate designs, intricate settings for gemstones, and fine chains.

3. Non-reactivity (Inertness): Gold and platinum are extremely unreactive. They do not tarnish or corrode when exposed to air or moisture, unlike many other metals. This means jewelry made from them will retain its shine and integrity for a very long time, even with regular wear. Silver is more reactive than gold and platinum and can tarnish (form silver sulfide), but it is still relatively resistant compared to many other metals and the tarnishing can be polished away.

4. Rarity and Value: While not a physical property of the metal itself, their rarity contributes to their perceived value and desirability, making them suitable for precious ornaments.

In summary, their beauty, ease of working with, and resistance to corrosion make platinum, gold, and silver ideal choices for crafting jewelry that is both aesthetically pleasing and durable.

Question:

What are the ions present in $Na⁢𝐴2⁢O$ and $MgO$ compounds?

Concept in a Minute:

Ionic compounds are formed by the electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions). To determine the ions present, we need to identify the constituent elements and their typical valencies or charges in ionic compounds.

Explanation:

The compound $Na⁢𝐴2⁢O$ is likely a typo and should be $Na_2O$. Let’s assume it is $Na_2O$.
Sodium (Na) is an alkali metal from Group 1 of the periodic table. Alkali metals tend to lose one electron to form a cation with a +1 charge. Therefore, sodium forms the $Na^+$ ion.
Oxygen (O) is a nonmetal from Group 16 of the periodic table. Nonmetals typically gain electrons to form anions. Oxygen usually gains two electrons to form an anion with a -2 charge. Therefore, oxygen forms the $O^{2-}$ ion.
In the compound $Na_2O$, to balance the charges, we need two $Na^+$ ions (total charge +2) for every one $O^{2-}$ ion (charge -2).
Thus, the ions present in $Na_2O$ are sodium ions ($Na^+$) and oxide ions ($O^{2-}$).

Magnesium (Mg) is an alkaline earth metal from Group 2 of the periodic table. Alkaline earth metals tend to lose two electrons to form a cation with a +2 charge. Therefore, magnesium forms the $Mg^{2+}$ ion.
Oxygen (O) is a nonmetal from Group 16 of the periodic table. As discussed above, oxygen usually gains two electrons to form an anion with a -2 charge. Therefore, oxygen forms the $O^{2-}$ ion.
In the compound $MgO$, the charges are balanced: one $Mg^{2+}$ ion (charge +2) and one $O^{2-}$ ion (charge -2).
Thus, the ions present in $MgO$ are magnesium ions ($Mg^{2+}$) and oxide ions ($O^{2-}$).

Ions present in $Na_2O$: $Na^+$ and $O^{2-}$
Ions present in $MgO$: $Mg^{2+}$ and $O^{2-}$

Question:

Show the formation of Na₂O by the transfer of electrons.

Concept in a Minute:

Ionic bond formation, electron transfer, noble gas configuration, oxidation states, chemical formula.

Explanation:

Sodium (Na) is an alkali metal with atomic number 11. Its electronic configuration is 2, 8, 1. It has one valence electron which it readily loses to achieve a stable noble gas configuration (like Neon). When it loses this electron, it forms a positively charged ion, Na⁺. The loss of this electron can be represented as:
Na → Na⁺ + e^–

Oxygen (O) is a non-metal with atomic number 8. Its electronic configuration is 2, 6. It needs two more electrons to achieve a stable noble gas configuration (like Neon). When it gains these electrons, it forms a negatively charged ion, O^2-. The gain of these electrons can be represented as:
O + 2e^– → O^2-

To form a neutral compound, the total positive charge must balance the total negative charge. Since sodium forms Na⁺ ions and oxygen forms O^2- ions, we need two sodium ions for every one oxide ion. This is because the +2 charge from two Na⁺ ions (2 × +1 = +2) will balance the -2 charge of the O^2- ion.

Therefore, the formation of sodium oxide (Na₂O) involves the transfer of electrons:
2Na → 2Na⁺ + 2e^–
O + 2e^– → O^2-

Combining these, we get:
2Na + O → 2Na⁺ + O^2- → Na₂O

In Na₂O, the sodium ions (Na⁺) and the oxide ion (O^2-) are held together by strong electrostatic forces of attraction, which constitute an ionic bond.

Question:

Write the electron-dot structures for sodium, oxygen and magnesium.

Concept in a Minute:

Electron-dot structures, also known as Lewis dot structures, represent the valence electrons of an atom. Valence electrons are the electrons in the outermost shell of an atom, which are involved in chemical bonding. To draw an electron-dot structure, we first need to determine the number of valence electrons for each element. This can be found using the group number in the periodic table. For elements in Group 1, there is 1 valence electron. For Group 2, there are 2 valence electrons. For Group 16 (or VIA), there are 6 valence electrons. For Group 17 (or VIIA), there are 7 valence electrons. For Group 18 (or VIIIA), there are 8 valence electrons (except for Helium, which has 2).

Explanation:

To write the electron-dot structures for sodium, oxygen, and magnesium, we need to identify their valence electrons.

Sodium (Na):
Sodium is in Group 1 of the periodic table. Therefore, it has 1 valence electron. The electron-dot structure for sodium is represented by the symbol ‘Na’ with a single dot around it.

•
Na

Oxygen (O):
Oxygen is in Group 16 of the periodic table. Therefore, it has 6 valence electrons. The electron-dot structure for oxygen is represented by the symbol ‘O’ with six dots around it. We usually pair up electrons as we fill them.

..
:O:
..

Magnesium (Mg):
Magnesium is in Group 2 of the periodic table. Therefore, it has 2 valence electrons. The electron-dot structure for magnesium is represented by the symbol ‘Mg’ with two dots around it.

.
Mg
.

Question:

Give two examples of amphoteric oxides.

Concept in a Minute:

Amphoteric oxides are oxides that exhibit both acidic and basic properties. This means they can react with both acids and bases.

Explanation:

Amphoteric oxides are a fascinating class of compounds that bridge the gap between acidic and basic oxides. They achieve this dual nature because their constituent elements can behave in different ways depending on the chemical environment.

When an amphoteric oxide reacts with an acid, it acts as a base. For instance, it will neutralize the acid.

When an amphoteric oxide reacts with a base, it acts as an acid. It will react with the base to form a salt and water.

The ability to act as both an acid and a base arises from the nature of the bonding and the oxidation states of the elements within the oxide. For example, oxides of elements like aluminum, zinc, lead, and tin in intermediate oxidation states often display amphoteric behavior.

Two common examples of amphoteric oxides are:

1. Aluminum oxide (Al2O3):
* Reaction with an acid: Al2O3 + 6HCl → 2AlCl3 + 3H2O (Al2O3 acts as a base)
* Reaction with a base: Al2O3 + 2NaOH + 3H2O → 2Na[Al(OH)4] (Al2O3 acts as an acid)

2. Zinc oxide (ZnO):
* Reaction with an acid: ZnO + 2HCl → ZnCl2 + H2O (ZnO acts as a base)
* Reaction with a base: ZnO + 2NaOH + H2O → Na2[Zn(OH)4] (ZnO acts as an acid)

Question:

Answer the following question.

What are alloys?

Concept in a Minute:

Alloys are mixtures, specifically homogeneous mixtures, of metals with other elements. These other elements can be metals or non-metals. The purpose of creating alloys is to improve the properties of the base metal, such as strength, hardness, or resistance to corrosion.

Explanation:

Alloys are solid solutions formed by combining two or more elements, at least one of which is a metal. This combination is typically achieved by melting the constituent elements together and then allowing the mixture to cool and solidify. The resulting material exhibits properties that are often superior to those of the individual constituent elements. For instance, pure iron is relatively soft and rusts easily, but when mixed with a small amount of carbon, it forms steel, which is much harder and more durable. Similarly, copper and zinc combine to form brass, which is more malleable than copper and resists corrosion better.

Examples of alloys and their uses:
* Steel (Iron + Carbon): Construction, tools, vehicles.
* Brass (Copper + Zinc): Decorative items, musical instruments, plumbing fixtures.
* Bronze (Copper + Tin): Sculptures, coins, bearings.
* Stainless Steel (Iron + Chromium + Nickel): Utensils, surgical instruments, industrial equipment.
* Solder (Tin + Lead): Joining electronic components.

Question:

Define the following term.

Mineral

Concept in a Minute:

Minerals are naturally occurring solid substances with a definite chemical composition and a crystalline structure. They are the building blocks of rocks and play a crucial role in various natural processes and human activities.

Explanation:

A mineral is defined as a naturally occurring, inorganic solid that has a definite chemical composition and an ordered atomic arrangement (crystalline structure). This means:
Naturally occurring: It is formed by natural geological processes, not synthesized in a laboratory.
Inorganic: It is not made from living organisms.
Solid: It is a rigid substance with a fixed shape and volume.
Definite chemical composition: It has a specific chemical formula, though some minerals can have a range of compositions within defined limits (solid solution).
Ordered atomic arrangement: The atoms within the mineral are arranged in a repeating, three-dimensional pattern, which gives it a characteristic crystalline structure. This structure influences its physical properties like hardness, cleavage, and crystal shape.

Example: Quartz (SiO2) is a mineral. It is naturally occurring, inorganic, solid, has a definite chemical composition (silicon and oxygen in a 1:2 ratio), and its atoms are arranged in a specific crystalline lattice.

Question:

Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Concept in a Minute:

Reactivity Series of Metals: Metals are arranged in a reactivity series based on their tendency to lose electrons. Metals above hydrogen in the reactivity series are more reactive than hydrogen and can displace it from dilute acids. Metals below hydrogen in the reactivity series are less reactive and cannot displace hydrogen.

Explanation:

Metals that are more reactive than hydrogen in the electrochemical series will displace hydrogen from dilute acids. This happens because these metals have a greater tendency to lose electrons and form positive ions, which then react with the hydrogen ions in the acid to liberate hydrogen gas. Examples of such metals include sodium, potassium, calcium, magnesium, aluminum, zinc, and iron.

Metals that are less reactive than hydrogen in the electrochemical series will not displace hydrogen from dilute acids. These metals have a lower tendency to lose electrons and cannot overcome the attraction between hydrogen ions and electrons in the acid solution. Examples of such metals include copper, silver, gold, and platinum.

Therefore, two metals that will displace hydrogen from dilute acids are zinc and iron.
Two metals that will not displace hydrogen from dilute acids are copper and silver.

Question:

Show the formation of MgO by the transfer of electrons.

Concept in a Minute:

Ionic bonding, electron transfer, formation of ions from atoms, cation, anion, electrostatic attraction.

Explanation:

Magnesium (Mg) is a metal in Group 2 of the periodic table. It has 2 valence electrons. Oxygen (O) is a non-metal in Group 16 of the periodic table. It has 6 valence electrons. To achieve a stable octet configuration, magnesium atom readily loses its 2 valence electrons to become a positively charged ion (cation) with a +2 charge, Mg$^{2+}$.

Mg $\rightarrow$ Mg$^{2+}$ + 2e$^-$

Oxygen atom needs to gain 2 electrons to achieve a stable octet. It accepts the 2 electrons lost by the magnesium atom to become a negatively charged ion (anion) with a -2 charge, O$^{2-}$.

O + 2e$^-$ $\rightarrow$ O$^{2-}$

The positively charged magnesium ion (Mg$^{2+}$) and the negatively charged oxide ion (O$^{2-}$) are held together by strong electrostatic forces of attraction, forming an ionic bond. This results in the formation of magnesium oxide (MgO), an ionic compound. The overall reaction can be represented as:

2Mg + O$_2$ $\rightarrow$ 2MgO

In terms of electron transfer:
Mg $\rightarrow$ Mg$^{2+}$ + 2e$^-$
O + 2e$^-$ $\rightarrow$ O$^{2-}$
Mg$^{2+}$ + O$^{2-}$ $\rightarrow$ MgO

Question:

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Concept in a Minute:

The key concept is the reaction between acids and metal oxides/carbonates to form soluble salts. Specifically, copper vessels react with oxygen and moisture in the air to form copper oxide and copper carbonate, which appear as a dull green or black layer. Sour substances like lemon juice and tamarind juice contain acids (citric acid and tartaric acid, respectively) that react with these copper compounds, dissolving them and restoring the shiny appearance of the copper.

Explanation:

Tarnished copper vessels have a dull coating of copper oxide and copper carbonate. These compounds are generally insoluble in water. Lemon juice contains citric acid, and tamarind juice contains tartaric acid. Both citric acid and tartaric acid are mild acids. When these sour substances are rubbed on the tarnished copper vessel, the acid reacts with the copper oxide and copper carbonate. This reaction converts the insoluble copper compounds into soluble copper salts. For example, copper carbonate reacts with citric acid to form copper citrate, which is soluble and can be easily washed away with water. This process removes the tarnish, revealing the shiny copper underneath.

Question:

Write equations for the reactions of calcium and potassium with water.

Concept in a Minute:

Reactivity of alkali and alkaline earth metals with water.
Alkali metals (Group 1) are highly reactive with water, producing hydrogen gas and a metal hydroxide.
Alkaline earth metals (Group 2) are less reactive than alkali metals, but still react with water to form hydrogen gas and a metal hydroxide. The reactivity increases down the group.

Explanation:

Calcium (Ca) is an alkaline earth metal from Group 2. Potassium (K) is an alkali metal from Group 1. Alkali metals are more reactive than alkaline earth metals.

Reaction of Calcium with Water:
Calcium reacts with cold water to form calcium hydroxide and hydrogen gas.
The balanced chemical equation for this reaction is:
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Calcium hydroxide is sparingly soluble in water, so it forms a suspension.

Reaction of Potassium with Water:
Potassium reacts vigorously with cold water to form potassium hydroxide and hydrogen gas. The reaction is so exothermic that the hydrogen gas produced often ignites, causing a small explosion.
The balanced chemical equation for this reaction is:
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)
Potassium hydroxide is soluble in water.

Question:

Why do ionic compounds have high melting points?

Concept in a Minute:

Ionic compounds are formed by electrostatic attraction between oppositely charged ions. The strength of this attraction determines properties like melting point. Factors influencing electrostatic attraction include the magnitude of charges and the distance between ions.

Explanation:

Ionic compounds have high melting points because of the strong electrostatic forces of attraction between the positively charged cations and negatively charged anions that hold them together in a crystal lattice. To melt an ionic compound, a significant amount of energy is required to overcome these strong forces and break the ionic bonds. The strength of these forces depends on the magnitude of the charges on the ions (higher charges lead to stronger attraction) and the distance between the ions (smaller ions and closer proximity lead to stronger attraction). Therefore, it takes a lot of heat, hence a high temperature, to provide enough kinetic energy to the ions to overcome these strong electrostatic attractions and transition from a solid, ordered lattice structure to a liquid state where ions are more mobile.

Question:

What are amphoteric oxides?

Concept in a Minute:

Acidic Oxides: Oxides that react with bases to form salt and water.
Basic Oxides: Oxides that react with acids to form salt and water.
Amphoteric: Possessing characteristics of both acidic and basic substances.

Explanation:

Amphoteric oxides are a special class of chemical compounds, specifically oxides, that exhibit dual behavior. They can react with both acids and bases. When an amphoteric oxide reacts with an acid, it behaves like a base, forming a salt and water. Conversely, when it reacts with a base, it acts like an acid, also forming a salt and water. This ability to react with both strong acids and strong bases is the defining characteristic of amphoteric oxides.

Common examples of amphoteric oxides include:
Aluminum oxide (Al2O3)
Zinc oxide (ZnO)
Lead oxide (PbO)
Tin oxide (SnO)
Gallium oxide (Ga2O3)

For instance, zinc oxide (ZnO) reacts with hydrochloric acid (an acid) to form zinc chloride and water:
ZnO + 2HCl → ZnCl2 + H2O

And it reacts with sodium hydroxide (a base) to form sodium zincate and water:
ZnO + 2NaOH + H2O → Na2[Zn(OH)4]

Question:

Write two methods of preventing the rusting of iron.

Concept in a Minute:

Rusting is the corrosion of iron, a process where iron reacts with oxygen and moisture to form hydrated iron(III) oxide. Preventing rusting involves creating a barrier between iron and these elements or altering the iron’s chemical nature to make it less reactive.

Explanation:

Here are two methods of preventing the rusting of iron:

1. Alloying with other metals: Iron can be mixed with other metals like chromium and nickel to form stainless steel. Stainless steel is much more resistant to rusting because the chromium forms a protective oxide layer on the surface of the steel, preventing further corrosion.

2. Galvanization: This method involves coating the iron object with a thin layer of zinc. Zinc is more reactive than iron and will preferentially corrode, forming a protective layer of zinc oxide and zinc carbonate. This layer acts as a barrier, preventing oxygen and moisture from reaching the iron surface. Even if the zinc coating is scratched, the zinc will continue to protect the iron by acting as a sacrificial anode.

Question:

In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Concept in a Minute:

Electrolytic refining uses electrolysis to purify impure metals. The impure metal is made the anode, a thin strip of pure metal is made the cathode, and an aqueous solution containing ions of the metal to be refined is used as the electrolyte. During electrolysis, impure metal at the anode dissolves, and pure metal deposits at the cathode.

Explanation:

In the electrolytic refining of a metal M:
Anode: The impure metal M is used as the anode. This is because during electrolysis, the impure metal at the anode will lose electrons and dissolve into the electrolyte as M ions.
Cathode: A thin strip of pure metal M is used as the cathode. This is where the pure metal ions from the electrolyte will gain electrons and deposit as pure metal.
Electrolyte: An aqueous solution of a salt of the metal M is used as the electrolyte. This solution provides the ions of metal M that are necessary for the deposition of pure metal at the cathode. For example, if the metal is copper, the electrolyte would be copper sulfate solution.

Question:

Which gas is produced when dilute hydrochloric acid is added to a reactive metal?

Concept in a Minute:

Acid-metal reactions, specifically the reaction between a dilute acid and a reactive metal. This reaction typically produces a salt and a gas. The identity of the gas is crucial.

Explanation:

When a dilute acid, such as dilute hydrochloric acid (HCl), is added to a reactive metal (a metal that is above hydrogen in the reactivity series), a chemical reaction takes place. In this reaction, the metal displaces hydrogen from the acid. The general balanced chemical equation for this reaction is:

Reactive Metal + Dilute Acid → Salt + Hydrogen Gas

For example, if we consider the reaction of zinc (Zn), a reactive metal, with dilute hydrochloric acid:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Here, zinc chloride (ZnCl₂) is the salt formed, and hydrogen gas (H₂) is produced. Hydrogen gas is a colorless and odorless gas that burns with a pop sound. This is a characteristic test for hydrogen gas. Therefore, the gas produced when dilute hydrochloric acid is added to a reactive metal is hydrogen.

Question:

Name two metals which are found in nature in the free state.

Concept in a Minute:

Reactivity Series of Metals: Metals differ in their reactivity. Highly reactive metals tend to react with substances in their surroundings (like oxygen, water, acids) to form compounds. Less reactive metals are less prone to chemical reactions and thus are found in nature in their elemental or free state.

Explanation:

Metals that are found in nature in the free state are those that are very unreactive. They do not readily combine with other elements to form compounds. This low reactivity means they exist as pure metals or as native elements.

Two examples of such metals are gold and platinum. These metals are known for their inertness and are found in the earth’s crust in their uncombined form. Other noble metals like silver can also be found in a relatively free state, though it can sometimes form compounds.

Common metals like iron, copper, zinc, and aluminum are much more reactive. They are found in nature as ores, which are compounds like oxides, sulfides, or carbonates.

Question:

What type of oxides are formed when non-metals combine with oxygen?

Concept in a Minute:

Non-metals are elements that tend to gain electrons or share electrons when forming chemical bonds. When they react with oxygen, they form oxides. The nature of the oxide formed (acidic, basic, or neutral) depends on the non-metal and the oxidation state of the element in the oxide. Generally, non-metal oxides exhibit acidic properties.

Explanation:

When non-metals combine with oxygen, they form non-metal oxides. These oxides are typically acidic in nature. This means that when they react with water, they form acids, or when they react with bases, they neutralize the base to form salt and water. For example, sulfur dioxide (SO2) reacts with water to form sulfurous acid (H2SO3). Carbon dioxide (CO2) reacts with water to form carbonic acid (H2CO3). Some non-metal oxides, like carbon monoxide (CO) and nitrous oxide (N2O), are neutral and do not exhibit acidic or basic properties. However, the general trend for non-metal oxides is acidity.

Question:

Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Concept in a Minute:

The question tests the understanding of material properties and their suitability for specific applications. Key properties to consider are reactivity with water and heat, and conductivity.

Explanation:

Copper is preferred over steel for hot water tanks primarily due to its superior resistance to corrosion. When exposed to hot water, steel (an alloy of iron) tends to rust or corrode more readily. This corrosion can lead to contamination of the water and weakening of the tank material over time. Copper, on the other hand, forms a protective patina layer that prevents further significant corrosion in water. While steel might be cheaper, the longevity and water quality provided by copper make it a more suitable choice for hot water tanks, despite copper being a better conductor of heat, which is also beneficial for efficient heating of water.

Question:

Write the chemical reaction when iron reacts with dilute H₂SO₄.

Concept in a Minute:

Acids react with reactive metals to produce a salt and hydrogen gas. The general reaction is: Metal + Acid -> Salt + Hydrogen Gas. Iron is a reactive metal. Dilute sulfuric acid is a common acid.

Explanation:

When iron (Fe) reacts with dilute sulfuric acid (H₂SO₄), a chemical reaction occurs. Iron is a metal that is more reactive than hydrogen. Acids contain hydrogen ions (H⁺). In this reaction, the iron displaces the hydrogen from the sulfuric acid. The iron atom loses two electrons and forms an iron(II) ion (Fe²⁺). These iron(II) ions then combine with sulfate ions (SO₄²⁻) from the sulfuric acid to form iron(II) sulfate (FeSO₄), which is a salt. The displaced hydrogen atoms gain electrons and combine to form hydrogen gas (H₂).

The balanced chemical equation for this reaction is:
Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)

Question:

Write equations for the reactions of iron with steam.

Concept in a Minute:

Reactions of metals with steam: Some reactive metals can react with steam at high temperatures to produce metal oxides and hydrogen gas. The reactivity of the metal determines whether this reaction occurs and at what temperature. Iron is a moderately reactive metal.

Explanation:

When iron is heated strongly and comes into contact with steam, it reacts to form iron(II,III) oxide (also known as magnetic iron oxide) and hydrogen gas. This reaction requires high temperatures, typically around 500-600°C, to proceed at a significant rate.

The balanced chemical equation for the reaction of iron with steam is:

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

In this reaction:
– Fe represents solid iron.
– H₂O represents steam (water in gaseous form).
– Fe₃O₄ represents iron(II,III) oxide, a black solid.
– H₂ represents hydrogen gas.

Question:

Give an example of a metal which is a poor conductor of heat.

Concept in a Minute:

Metals are generally good conductors of heat due to the presence of free electrons that can easily transfer thermal energy. However, some metals exhibit significantly lower thermal conductivity compared to others, making them poor conductors relative to the typical metallic standard.

Explanation:

While most metals are excellent conductors of heat, there are exceptions. Some metals have a crystalline structure or electronic configuration that hinders the free movement of electrons and the vibration of atoms, which are the primary mechanisms for heat transfer. Therefore, they conduct heat poorly.

Example: Lead (Pb) is a metal that is a poor conductor of heat. Other examples include mercury (though it’s a liquid metal at room temperature, it’s still a metal) and alloys containing these metals.

Question:

What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.

Concept in a Minute:

Reactivity Series of Metals: Metals have different tendencies to lose electrons (reactivity). A more reactive metal can displace a less reactive metal from its salt solution.

Explanation:

When zinc is added to a solution of iron (II) sulphate, you will observe no significant reaction. This is because zinc is less reactive than iron. According to the reactivity series of metals, iron is above zinc, meaning iron is more reactive than zinc. Therefore, zinc cannot displace iron from its iron (II) sulphate solution.

The chemical reaction would be:
Zn(s) + FeSO4(aq) → No Reaction

If the question were reversed, and iron was added to zinc sulphate solution, a reaction would occur because iron is more reactive than zinc, and would displace zinc.

Question:

Give an example of a metal which can be easily cut with a knife.

Concept in a Minute:

The softness of metals is related to their atomic structure and the way their atoms are bonded. Metals that are very soft have weaker metallic bonds, allowing their layers of atoms to slide over each other more easily, making them malleable and ductile, and thus easy to cut.

Explanation:

The question asks for an example of a metal that can be easily cut with a knife. This property is related to the softness of the metal. Some metals are significantly softer than others. Alkali metals, for instance, are known for their extreme softness. Sodium is a classic example of such a metal. It is soft enough to be easily cut with a knife. Other alkali metals like potassium and lithium are also very soft and can be cut with a knife.

Example: Sodium

Question:

Explain the meaning of ductile.

Concept in a Minute:

Ductility is a material property. It describes how a material behaves when subjected to stress. Specifically, it relates to the ability to deform plastically without fracturing.

Explanation:

Ductile means that a material can be stretched, drawn, or hammered into a thin wire or sheet without breaking. This is a characteristic property of many metals, such as copper, aluminum, and iron. When a ductile material is put under tensile stress (a pulling force), it can undergo significant plastic deformation (permanent change in shape) before it eventually fractures. This plastic deformation means the material changes its shape permanently rather than snapping.

Question:

Give an example of a metal which is a liquid at room temperature.

Concept in a Minute:

States of Matter, Melting Point, Room Temperature. The question requires knowledge of the common states of elements at standard room temperature and pressure, specifically focusing on metals and their melting points.

Explanation:

Room temperature is generally considered to be around 25 degrees Celsius (298 Kelvin). Most metals are solids at this temperature because their melting points are significantly above room temperature. However, there are a few exceptions. Mercury is a metal that has a melting point of -38.83 degrees Celsius, which is well below room temperature. Therefore, at room temperature, mercury exists as a liquid.

Example: Mercury

Question:

Define the Ore.

Concept in a Minute:

Minerals and Ores are related to naturally occurring substances from which metals can be extracted. The key difference lies in the economic viability and concentration of the desired metal.

Explanation:

An ore is a naturally occurring rock or mineral deposit that contains a sufficient concentration of a valuable mineral or metal, which can be economically extracted profitably. It is essentially a source material from which a metal or a valuable mineral can be extracted using various physical or chemical processes. In simpler terms, it’s a rock that holds a metal that we can dig up and process to get that metal, and it’s worth the effort to do so.

Question:

Why is sodium kept immersed in kerosene oil?

Concept in a Minute:

Reactivity of alkali metals with air and water.
Oxidation and reduction.
Properties of kerosene.

Explanation:

Sodium is an alkali metal and is highly reactive. It reacts vigorously with oxygen in the air, leading to rapid oxidation and potentially catching fire. It also reacts explosively with water, producing hydrogen gas and a significant amount of heat. Kerosene is a hydrocarbon and is non-polar. It does not react with sodium. By immersing sodium in kerosene, it is kept away from contact with air (oxygen) and moisture, thus preventing these dangerous reactions and keeping the sodium safe. Kerosene acts as a protective layer.

Question:

Define the following term.

Gangue

Concept in a Minute:

Minerals and Ores: Understanding that ores are naturally occurring substances from which metals can be extracted economically, and that these ores often contain impurities.
Impurities in Ores: Recognizing that these impurities are unwanted materials mixed with the desired ore.

Explanation:

Gangue refers to the worthless, earthy, or stony materials that are mixed with an ore and are of no commercial value. These impurities, such as sand, clay, rocks, and other unwanted minerals, need to be removed from the ore before the metal can be extracted. The process of removing gangue from the ore is called ore dressing or benefaction.

Question:

Give an example of a metal which is the best conductor of heat.

Concept in a Minute:

Metals are generally good conductors of heat due to the presence of free electrons that can easily transfer kinetic energy. The ability of a metal to conduct heat is quantified by its thermal conductivity.

Explanation:

The question asks for an example of a metal that is the best conductor of heat. Among the commonly known metals, silver has the highest thermal conductivity. This means that heat can pass through silver more readily than through other metals. Therefore, silver is considered the best conductor of heat. Other metals like copper and gold are also excellent conductors of heat, but silver surpasses them.

Question:

Give reasons.

Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

Concept in a Minute:

Reactivity of metals and formation of protective layers.

Explanation:

Although aluminium is a highly reactive metal, it reacts with oxygen in the air to form a thin, tough, and unreactive layer of aluminium oxide (Al₂O₃) on its surface. This protective oxide layer prevents further reaction of the aluminium metal with air or food. This layer is impermeable and adheres strongly to the underlying metal, making it resistant to corrosion and suitable for use in cooking utensils. The high melting point and good thermal conductivity of aluminium also contribute to its suitability for cookware.

Question:

Explain the meaning of malleable.

Concept in a Minute:

Malleability is a physical property of materials, primarily metals. It describes their ability to deform under compressive stress without fracturing.

Explanation:

Malleable materials can be hammered or rolled into thin sheets. This means that when a force is applied to them, they can change their shape without breaking. Think of how gold can be beaten into very thin gold leaf, or how aluminum foil is made. These are examples of malleable materials. The ability to be shaped into thin sheets is the defining characteristic of malleability.

Question:

Give reason:

Sodium, potassium and lithium are stored under oil.

Concept in a Minute:

Reactivity of alkali metals with air and water.

Explanation:

Sodium, potassium, and lithium are alkali metals. Alkali metals are highly reactive elements. They react vigorously with oxygen in the air and with moisture (water). This reaction can be exothermic, meaning it releases heat, and can even lead to ignition or explosion if exposed to air or water. To prevent these dangerous reactions, these metals are stored under oil. Oil acts as a barrier, preventing them from coming into contact with oxygen and moisture in the atmosphere.

Next Chapter: Our Environment

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