Chemical Reactions And Equations - MCQ Test, Class 10 Science Solved MCQs

Heating lead nitrate produces two gases:

• Nitrogen dioxide (NO₂)
• Oxygen (O₂)

During the decomposition of lead nitrate, these gases are released due to the breakdown of its chemical structure when exposed to heat.

H₂ + O₂ → H₂O

When electric current is passed, we get water as by product. This is basis of fuel cell. At the cathode, the electrons and the hydrogen ions combine with oxygen to make water, which then flows out of the cell.

A fuel cell takes in hydrogen and oxygen and produces electricity, with water and heat as byproducts.

Match the following with correct response.

• Oxidation: Refers to the loss of electrons from a species.
• Reduction: Involves the gain of electrons by a species.
• Reducing agent: This is the electron-losing species that donates electrons in a reaction.
• Oxidising agent: This is the electron-accepting species that gains electrons in a reaction.

A double displacement reaction involves two compounds exchanging ions (AB + CD → AD + CB). C (NaCl + AgNO₃ → NaNO₃ + AgCl) shows Na⁺ and Ag⁺ swapping partners. A, B, and D are synthesis reactions, not double displacement.

The solution obtained from dissolving copper sulphate crystals in water will have a distinctive colour.

• The resulting solution will appear blue.
• This blue colour is characteristic of copper sulphate due to its chemical properties.
• When dissolved, the copper ions impart this vibrant hue to the solution.

In the reaction involving magnesium ribbon burning in air, the following occurs:

• Magnesium reacts with oxygen, resulting in a bright flame.
• This process produces a white substance known as magnesium oxide.
• During this reaction, magnesium undergoes a change in its oxidation state.
• Specifically, magnesium is oxidised as it loses electrons to oxygen.

Thus, magnesium is not reduced; it is solely oxidised in this reaction.

When dilute hydrochloric acid (HCl) is added to iron filings, a chemical reaction occurs.

• The reaction produces hydrogen gas and iron chloride.
• This is a typical reaction between an acid and a metal.
• The iron filings react with the acid, resulting in the formation of these products.

Match the following with correct response.

• Chemical change:Rusting of iron
• Physical change:Dissolution of sugar or salt in water
• Exothermic:Energy releasing
• Endothermic:Energy absorbed

In ZnO + CO → Zn + CO₂, ZnO loses oxygen (Zn²⁺ to Zn⁰), indicating reduction. CO gains oxygen (C²⁺ to C⁴⁺), indicating oxidation. Thus, only D (ZnO is being reduced) is correct.

Zinc metal has a shiny, silvery appearance in its pure form, though it may dull slightly upon exposure to air due to oxide formation.

The reactions where a more reactive element displaces a less reactive element from a compound are known as:

• Displacement reactions

These reactions occur in various scenarios, including:

• A more reactive metal replacing a less reactive metal in a compound.
• An element taking the place of another in a solution, leading to the formation of a new compound.

Understanding these reactions is essential for predicting chemical behaviour and reactivity in various contexts.

The colour of copper sulphate solution changes when an iron nail is dipped in it due to a chemical reaction. This reaction is classified as a:

• Displacement reaction because iron displaces copper from copper sulphate.
• The iron nail reacts with copper ions in the solution.
• This leads to the formation of iron sulphate and the deposition of copper on the nail.
• The change in colour indicates the presence of copper metal and the new iron sulphate solution.

1. Gain of hydrogen: This process is referred to as Reduction.

2. Loss of hydrogen: This process is known as Oxidation.

3. Unpleasant taste and foul smell in fatty food: This is called Rancidity.

4. Eating away of metal in the presence of air and moisture: This phenomenon is termed Corrosion.

This reaction is an example of a:

• Displacement reaction: In this type of reaction, one element displaces another in a compound.
• Here, aluminium replaces iron in iron(III) oxide (Fe₂O₃), resulting in the formation of aluminium oxide (Al₂O₃) and iron (Fe).
• This process showcases the reactivity of aluminium, which is more reactive than iron.

A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more elements or new compounds which is occuring in option (c) only.

To identify the gas produced when diluted HCl reacts with zinc metal, the following method can be used:

• Gaseous Product: The reaction produces hydrogen gas (H₂).
• Testing Method: Bring a burning splinter close to the gas. If it ignites with a 'pop' sound, hydrogen gas is confirmed.
• Other Indicators: Blue and red litmus solutions are not suitable for identifying this gas.
• Lime Water: This is used to test for carbon dioxide, which is not relevant in this case.

Ferrous sulphate (2FeSO₄) decomposes when heated: 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃. Heat is the primary condition; light or catalysts are not typically required.

When Copper (Cu) is added to Silver nitrate (AgNO₃) solution, a displacement reaction occurs because copper is more reactive than silver.
Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag
Copper displaces silver, forming copper(II) nitrate 

So, Correct Option: (C)

Match the following terms with their correct definitions:

• Combination Reaction: When two substances react to form a new product.
• Decomposition: A process where a compound breaks down into two or more simpler substances.
• Displacement Reaction: Occurs when a more reactive metal displaces a less reactive metal from a compound.
• Redox Reaction: Involves the loss or gain of electrons during the reaction.

When iron nails are immersed in an aqueous solution of copper sulphate, several observations can be made about the reaction:

• Blue colour: The blue colour of the solution fades as copper ions are displaced.
• Iron nails: The nails develop a brownish tint due to the deposition of copper.
• Displacement reaction: This is indeed a displacement reaction, where iron replaces copper.
• Dissolution: Iron nails do not completely dissolve in the solution.

Only option A shows the metathesis (double displacement) reaction.

To determine which equation is not balanced, we can analyse each option:

• A: Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)
  • Balanced: 1 Mg, 1 Cu, 1 SO₄ on both sides.
• B: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
  • Balanced: 1 Zn, 1 SO₄, 2 H on both sides.
• C: Ca(OH)₂(l) + CO₂(g) → CaCO(s) + H₂O(l)
  • Not balanced: 1 Ca, 1 C, 2 O on the left, but 1 Ca, 1 C, 3 O on the right.
• D: Fe(s) + Cl₂(g) → FeCl₂(s)
  • Balanced: 1 Fe, 2 Cl on both sides.

Conclusion: The unbalanced equation is option C.

The compound formed by Hg⁺² and Cl^- is:

• The cation Hg⁺² has a charge of +2.
• The anion Cl^- has a charge of -1.
• To balance the charges, two chloride ions are needed for each mercury ion.
• The resulting compound is HgCl₂, known as mercury(II) chloride.

Answer: C (CO₂)

Solution: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Carbon dioxide (CO₂) is released as a gas.

Quick lime is added to water:

• The reaction produces calcium hydroxide, represented as Ca(OH)₂.

Formula for rust:

• Rust is primarily composed of iron oxide, denoted as Fe₂O₃.xH₂O.

Silver tarnishing:

• This occurs due to the formation of silver sulfide, which is represented as H₂S gas.

Pop sound:

• A characteristic pop sound is produced when hydrogen gas is ignited.

When zinc metal is added to various solutions, the following observations can be made:

• Al₂(SO₄)₃: No reaction occurs, as zinc does not displace aluminium.
• FeSO₄: Zinc can displace iron due to its higher position in the reactivity series, leading to a reaction.
• H₂SO₄: Zinc reacts with sulphuric acid, producing hydrogen gas and zinc sulfate.
• CuSO₄: Zinc displaces copper in this solution, resulting in a visible reaction.

Conclusion: The test tube containing Al₂(SO₄)₃ shows no change when zinc is added.

Can we store CuSO₄ in an iron container and why?

No, storing CuSO₄ in an iron container is not advisable due to the following reasons:

• Reactivity: Iron is more reactive than copper.
• Potential Reaction: When in contact, iron can react with CuSO₄, leading to possible corrosion of the container.
• Contamination Risk: This reaction could contaminate the solution with iron ions.

For these reasons, it is better to use a container made of a less reactive material for storing CuSO₄.

When hydrogen sulfide (H₂S) burns in air, it reacts to produce certain products.

During this combustion process, the following occurs:

• H₂S reacts with oxygen from the air.
• This reaction primarily produces water (H₂O) and sulfur dioxide (SO₂).

Although sulfur trioxide (SO₃) can form under specific conditions, the main products from the complete combustion of H₂S in air are water and sulfur dioxide.

Reaction:

3Fe (s) + 4H₂O (g) → Fe₃O₄ (s) + 4H₂ (g)

Analysis of Statements:

1. Iron metal is getting oxidised:

   • Iron (Fe) starts in the elemental state (0) and forms Fe₃O₄, where it has mixed oxidation states (+2 and +3). This means iron is losing electrons (oxidation).
   • This statement is correct.

2. Water is getting reduced:

   • Water (H₂O) is reduced to hydrogen gas (H₂), as the oxygen in water helps oxidize iron. The hydrogen in water gains electrons to form H₂.
   • This statement is correct.

3. Water is acting as a reducing agent:

   • A reducing agent is a substance that donates electrons. In this reaction, water is accepting electrons (reduced to H₂), so it is not a reducing agent.
   • This statement is incorrect.

4. Water is acting as an oxidizing agent:

   • Water is causing the oxidation of iron by accepting electrons. Thus, it is an oxidizing agent.
   • This statement is correct.