Chemical reactions and equations Class 10th Solutions | Chemical reactions and equations Textbook Solution 10 Standard SSC Maharashtra State Board
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Choose the correct option from the bracket and explain the statement giving reason.
(Oxidation, displacement, electrolysis, reduction, zinc, copper, double displacement, decomposition)
To prevent rusting, a layer of ______ metal is applied on iron sheets.
Scientific and Written Exam Answer:
To prevent rusting, a layer of zinc metal is applied on iron sheets. This process is called galvanization.
Reason: Zinc acts as a protective layer and prevents iron from coming in direct contact with oxygen and moisture, which are responsible for rusting.
Simple and Understandable Answer:
Iron rusts when it comes into contact with air and water. To prevent this, we coat iron sheets with zinc. This layer stops rusting and keeps iron strong.
Example: Iron buckets, pipes, and roofing sheets are often galvanized with zinc to prevent rust.
Choose the correct option from the bracket and explain the statement giving reason.
(Oxidation, displacement, electrolysis, reduction, zinc, copper, double displacement, decomposition)
The conversion of ferrous sulphate to ferric sulphate is ______ reaction.
Scientific and Written Exam Answer:
The conversion of ferrous sulphate (FeSO₄) to ferric sulphate (Fe₂(SO₄)₃) is an oxidation reaction.
Reason: In this reaction, Fe²⁺ (ferrous ion) loses electrons and gets converted into Fe³⁺ (ferric ion), which is a process of oxidation.
Simple and Understandable Answer:
Oxidation happens when something loses electrons. In this case, ferrous sulphate turns into ferric sulphate by losing electrons.
Example: This reaction is similar to how iron rusts—it reacts with air and changes to a different form.
When electric current is passed through acidulated water, ______ of water takes place.
- Oxidation
- Displacement
- Electrolysis
- Reduction
- Zinc
- Copper
- Double displacement
- Decomposition
Scientific and Written Exam Answer:
When electric current is passed through acidulated water, electrolysis of water takes place.
Reason: Electrolysis is the process where water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) gases using an electric current.
The reaction follows the equation:
$$ 2H_2O \rightarrow 2H_2 + O_2 $$
Simple and Understandable Answer:
Water can be broken into hydrogen and oxygen when electricity is passed through it. This process is called electrolysis.
Example: Electrolysis is used to produce hydrogen gas for fuel and other industrial uses.
Choose the correct option from the bracket and explain the statement giving a reason.
(Oxidation, displacement, electrolysis, reduction, zinc, copper, double displacement, decomposition)
Addition of an aqueous solution of ZnSO₄ to an aqueous solution of BaCl₂ is an example of ______ reaction.
Scientific and Written Exam Answer:
The reaction between zinc sulfate (ZnSO₄) and barium chloride (BaCl₂) is a double displacement reaction.
Reason: In this reaction, the sulfate (SO₄²⁻) from ZnSO₄ and the chloride (Cl⁻) from BaCl₂ exchange their places, forming new compounds.
The reaction follows the equation:
$$ ZnSO_4 + BaCl_2 \rightarrow BaSO_4 \downarrow + ZnCl_2 $$
BaSO₄ forms as a white precipitate.
Simple and Understandable Answer:
In this reaction, the elements in two compounds swap places. This is called a double displacement reaction.
Example: Just like exchanging dance partners, ZnSO₄ and BaCl₂ switch their ions and form new substances.
Write answer to the following.
What is the reaction called when oxidation and reduction take place simultaneously? Explain with one example.
Scientific and Written Exam Answer:
The reaction in which oxidation and reduction occur simultaneously is called a Redox Reaction.
Oxidation: It is the process in which a substance loses electrons or gains oxygen.
Reduction: It is the process in which a substance gains electrons or loses oxygen.
Example:
Consider the reaction of zinc with copper sulfate:
$$ Zn + CuSO_4 \rightarrow ZnSO_4 + Cu $$- In this reaction, Zn (Zinc) loses electrons and gets oxidized to Zn2+.
- Cu2+ (Copper ion) gains electrons and gets reduced to Cu (Copper metal).
Thus, oxidation and reduction occur together in a redox reaction.
Simple and Understandable Answer:
A reaction in which one substance gains oxygen (oxidation) while another loses oxygen (reduction) at the same time is called a Redox Reaction.
Example: When an iron nail is placed in copper sulfate solution:
$$ Fe + CuSO_4 \rightarrow FeSO_4 + Cu $$- Iron (Fe) loses electrons and turns into Fe2+ (oxidation).
- Copper ions (Cu2+) gain electrons and turn into copper metal (reduction).
This reaction shows both oxidation and reduction happening together.
---How can the rate of the chemical reaction, namely, decomposition of hydrogen peroxide be increased?
Scientific and Written Exam Answer:
The decomposition of hydrogen peroxide (H2O2) is a slow reaction. Its rate can be increased using a catalyst, increasing temperature, or by increasing the surface area.
The reaction is:
$$ 2H_2O_2 \rightarrow 2H_2O + O_2 $$Ways to increase the rate:
- Adding a catalyst like manganese dioxide (MnO2), which speeds up the reaction.
- Increasing the temperature of the solution.
- Increasing the concentration of hydrogen peroxide.
Example: If a small amount of manganese dioxide is added to hydrogen peroxide, it rapidly breaks down into water and oxygen.
Simple and Understandable Answer:
Hydrogen peroxide breaks down slowly on its own, but we can make it faster using a few methods:
- Adding MnO2 (a special chemical called a catalyst) makes the reaction happen quickly.
- Warming up the solution increases the speed.
- Using a stronger solution of hydrogen peroxide speeds it up even more.
Example: If you pour hydrogen peroxide on a cut, it fizzes because it breaks down quickly and releases oxygen!
Explain the term reactant and product, giving examples.
Scientific and Written Exam Answer:
In a chemical reaction, substances that undergo a change are called Reactants, and the new substances formed are called Products.
Reactants: The initial substances that take part in a chemical reaction.
Products: The new substances formed as a result of the reaction.
Example: The reaction between hydrogen and oxygen to form water:
$$ 2H_2 + O_2 \rightarrow 2H_2O $$- Reactants: Hydrogen (H2) and Oxygen (O2).
- Product: Water (H2O).
Simple and Understandable Answer:
When two or more things react together to form something new, the original substances are called Reactants, and the new thing formed is called a Product.
Example: When you burn wood:
$$ Wood + Oxygen \rightarrow Ash + Carbon dioxide $$- Reactants: Wood and Oxygen.
- Products: Ash and Carbon dioxide.
Explain the types of reactions with reference to oxygen and hydrogen. Illustrate with examples.
Scientific and Written Exam Answer:
There are two main types of reactions involving oxygen and hydrogen:
1) Combination Reaction
A combination reaction occurs when two or more reactants combine to form a single product.
Example: The combination of hydrogen and oxygen to form water:
$$ 2H_2 + O_2 \rightarrow 2H_2O $$2) Decomposition Reaction
A decomposition reaction occurs when a single compound breaks down into simpler substances.
Example: The decomposition of water into hydrogen and oxygen using electrolysis:
$$ 2H_2O \rightarrow 2H_2 + O_2 $$Subtype 1: Oxidation and Reduction Reaction
Oxidation: When a substance gains oxygen or loses hydrogen.
Reduction: When a substance gains hydrogen or loses oxygen.
Example:
$$ 2Cu + O_2 \rightarrow 2CuO $$- Copper (Cu) gains oxygen to form Copper Oxide (CuO) (Oxidation).
Subtype 2: Reduction
Reduction occurs when a compound loses oxygen or gains hydrogen.
Example: The reduction of copper oxide by hydrogen:
$$ CuO + H_2 \rightarrow Cu + H_2O $$- Copper Oxide (CuO) loses oxygen and turns into Copper (Cu).
Explain the similarity and difference in two events, namely adding NaOH to water and adding CaO to water.
Scientific and Written Exam Answer:
Both reactions involve the addition of a basic compound to water, resulting in an exothermic reaction (heat is released).
1) Reaction of NaOH (Sodium Hydroxide) with Water:
NaOH dissolves in water and dissociates completely to form hydroxide ions (OH⁻), making the solution strongly alkaline.
$$ NaOH \rightarrow Na^+ + OH^- $$2) Reaction of CaO (Calcium Oxide) with Water:
CaO reacts with water to form slaked lime (Ca(OH)₂), which is slightly soluble in water and forms a milky suspension.
$$ CaO + H_2O \rightarrow Ca(OH)_2 $$Similarities:
- Both reactions produce hydroxides, making the solution basic.
- Both reactions release heat (exothermic reaction).
Differences:
- NaOH dissolves completely in water, while Ca(OH)₂ is only slightly soluble, forming a suspension.
- NaOH solution is a clear, strong base, whereas Ca(OH)₂ solution appears milky.
Simple and Understandable Answer:
Both NaOH (Sodium Hydroxide) and CaO (Calcium Oxide) make water basic when added.
Similarities:
- Both reactions produce a base.
- Both release heat when mixed with water.
Differences:
- NaOH dissolves completely, forming a clear solution.
- CaO forms a milky solution because it does not dissolve completely.
Example: If you add NaOH to water, it disappears completely, but if you add CaO, the water looks cloudy.
Explain the term with examples: Endothermic Reaction
Scientific and Written Exam Answer:
An endothermic reaction is a chemical reaction in which energy is absorbed from the surroundings, usually in the form of heat. This causes the temperature of the surroundings to decrease.
General Formula:
$$ Reactants + Heat \rightarrow Products $$Endothermic reactions require external energy to proceed because the bonds in the reactants need more energy to break than the energy released when new bonds form in the products.
Example 1: Decomposition of Calcium Carbonate
$$ CaCO_3 \xrightarrow{\text{Heat}} CaO + CO_2 $$Explanation:
- Calcium carbonate (CaCO₃) decomposes into calcium oxide (CaO) and carbon dioxide (CO₂) when heated.
- Heat is absorbed to break the bonds in CaCO₃.
Example 2: Photosynthesis
$$ 6CO_2 + 6H_2O + Light \rightarrow C_6H_{12}O_6 + 6O_2 $$Explanation:
- Plants absorb light energy from the Sun to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂).
- This is an endothermic process as it requires energy input.
Key Characteristics of Endothermic Reactions:
- Heat energy is absorbed from the surroundings.
- Temperature of the surroundings decreases.
- Usually occurs in thermal decomposition and biological processes like photosynthesis.
Simple and Understandable Answer:
An endothermic reaction is a reaction that needs heat energy to happen. If you touch the container where an endothermic reaction is occurring, it will feel cold because heat is being taken in.
Example 1: Cooking an Egg
When you fry an egg, heat is absorbed by the egg to cook it. Without heat, the egg remains raw.
Example 2: Melting Ice
$$ H_2O (s) + Heat \rightarrow H_2O (l) $$Explanation:
- Ice absorbs heat from the surroundings to turn into water.
- The process requires energy input, making it an endothermic reaction.
Tip: If a reaction makes things colder, it is likely an endothermic reaction!
Explain the term with examples: Combination Reaction
Scientific and Written Exam Answer:
A combination reaction is a type of chemical reaction in which two or more reactants combine to form a single product. This reaction is also known as a synthesis reaction.
General Formula:
$$ A + B \rightarrow AB $$Here, two different substances (A and B) combine to form a new single product (AB).
Example 1: Formation of Water
$$ 2H_2 + O_2 \rightarrow 2H_2O $$Explanation:
- Hydrogen gas (H₂) and oxygen gas (O₂) combine to form water (H₂O).
- This reaction releases energy and is an example of an exothermic combination reaction.
Example 2: Formation of Calcium Carbonate
$$ CaO + CO_2 \rightarrow CaCO_3 $$Explanation:
- Calcium oxide (CaO) reacts with carbon dioxide (CO₂) to form calcium carbonate (CaCO₃).
- This reaction is used in cement and limestone formation.
Key Characteristics of Combination Reactions:
- Two or more reactants combine to form a single product.
- Usually exothermic, meaning they release heat.
- Common in metal and non-metal reactions.
Simple and Understandable Answer:
A combination reaction happens when two or more substances join together to make one new substance.
Example 1: Making Salt
$$ Na + Cl_2 \rightarrow NaCl $$Explanation:
- Sodium (Na) and chlorine (Cl₂) combine to make common salt (NaCl).
- This is an example of a simple combination reaction.
Example 2: Making Lime Water
$$ CaO + H_2O \rightarrow Ca(OH)_2 $$Explanation:
- Calcium oxide (quicklime) reacts with water to form calcium hydroxide (slaked lime).
- This reaction releases heat and is used in construction.
Tip: If two things mix and become one, it is likely a combination reaction!
Explain the term with examples: Balanced Equation
Scientific and Written Exam Answer:
A balanced chemical equation is an equation in which the number of atoms of each element on the reactant side is equal to the number of atoms on the product side. This follows the law of conservation of mass, which states that mass can neither be created nor destroyed in a chemical reaction.
Example 1: Balanced Equation for the Formation of Water
$$ 2H_2 + O_2 \rightarrow 2H_2O $$Explanation:
- There are 4 hydrogen (H) atoms and 2 oxygen (O) atoms on both sides.
- This ensures that mass is conserved in the reaction.
Example 2: Balanced Equation for the Combustion of Methane
$$ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O $$Explanation:
- Carbon (C), hydrogen (H), and oxygen (O) atoms are equal on both sides.
- The equation follows the law of conservation of mass.
Key Characteristics of a Balanced Equation:
- The number of atoms of each element is the same on both sides.
- Follows the law of conservation of mass.
- Does not change the chemical nature of the reaction.
Simple and Understandable Answer:
A balanced equation makes sure that the same number of atoms of each element are present before and after a chemical reaction.
Example 1: Making Water
$$ 2H_2 + O_2 \rightarrow 2H_2O $$Explanation:
- Hydrogen (H) and oxygen (O) atoms are equal on both sides.
- This makes sure no atoms are lost or gained.
Example 2: Rusting of Iron
$$ 4Fe + 3O_2 \rightarrow 2Fe_2O_3 $$Explanation:
- Iron (Fe) and oxygen (O) atoms are equal on both sides.
- Rust (Fe₂O₃) is formed without losing or gaining atoms.
Tip: Always count the number of atoms on both sides to check if an equation is balanced!
Explain the term with examples: Displacement Reaction
Scientific and Written Exam Answer:
A displacement reaction is a type of chemical reaction in which a more reactive element displaces a less reactive element from its compound. These reactions usually occur between metals or halogens and follow the reactivity series.
Example 1: Displacement of Copper by Iron
$$ Fe + CuSO_4 \rightarrow FeSO_4 + Cu $$Explanation:
- Iron (Fe) is more reactive than copper (Cu).
- Iron displaces copper from copper sulfate (CuSO₄) to form iron sulfate (FeSO₄).
Example 2: Displacement of Zinc by Magnesium
$$ Mg + ZnSO_4 \rightarrow MgSO_4 + Zn $$Explanation:
- Magnesium (Mg) is more reactive than zinc (Zn).
- Magnesium replaces zinc from zinc sulfate (ZnSO₄), forming magnesium sulfate (MgSO₄).
Key Characteristics of Displacement Reactions:
- More reactive elements replace less reactive elements.
- Follows the reactivity series of metals.
- Commonly occurs in aqueous solutions.
Simple and Understandable Answer:
A displacement reaction happens when a stronger element pushes out a weaker element from a compound.
Example 1: Iron and Copper Sulfate
$$ Fe + CuSO_4 \rightarrow FeSO_4 + Cu $$Explanation:
- Iron is stronger than copper.
- Iron takes copper’s place, forming iron sulfate and leaving copper alone.
Example 2: Zinc and Hydrochloric Acid
$$ Zn + 2HCl \rightarrow ZnCl_2 + H_2 $$Explanation:
- Zinc replaces hydrogen in hydrochloric acid (HCl).
- Hydrogen gas is released, and zinc chloride (ZnCl₂) is formed.
Tip: Always check the reactivity series to see which element is stronger!
Give scientific reason:
When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky.
Scientific and Written Exam Answer:
When limestone (CaCO₃) is heated, it undergoes thermal decomposition to form calcium oxide (CaO) and carbon dioxide (CO₂):
$$ CaCO_3 \xrightarrow{\text{heat}} CaO + CO_2 $$The carbon dioxide (CO₂) gas released is passed through freshly prepared lime water (calcium hydroxide solution - Ca(OH)₂). A chemical reaction occurs, forming calcium carbonate (CaCO₃), which is insoluble in water and appears as a milky white precipitate.
$$ CO_2 + Ca(OH)_2 \rightarrow CaCO_3 \downarrow + H_2O $$Explanation:
- Heating limestone releases carbon dioxide (CO₂).
- When CO₂ is passed through lime water, it reacts with calcium hydroxide.
- This forms calcium carbonate (CaCO₃), which is insoluble and gives a milky appearance.
Simple and Understandable Answer:
When we heat limestone (CaCO₃), it gives off carbon dioxide (CO₂) gas. This gas is then passed through lime water (Ca(OH)₂ solution), which turns milky.
Why does this happen?
- CO₂ reacts with lime water and forms calcium carbonate (CaCO₃).
- Calcium carbonate is a white solid that does not dissolve in water.
- This makes the lime water look milky.
Example:
If you blow air (which contains CO₂) into lime water using a straw, it also turns milky because of the same reaction!
Give scientific reason:
It takes time for pieces of Shahabad tile to disappear in HCl, but its powder disappears rapidly.
Scientific and Written Exam Answer:
Shahabad tile is mainly composed of calcium carbonate (CaCO₃). When it reacts with hydrochloric acid (HCl), it forms calcium chloride (CaCl₂), water (H₂O), and carbon dioxide (CO₂):
$$ CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2 \uparrow $$The rate of this reaction depends on the surface area of the reactant. Smaller particles expose more surface area to the acid, allowing faster reaction.
Explanation:
- A solid piece of Shahabad tile has less surface area in contact with HCl, so the reaction is slower.
- When the tile is crushed into powder, the surface area increases significantly.
- More acid molecules come in contact with calcium carbonate, leading to a faster reaction.
Simple and Understandable Answer:
When we put a Shahabad tile in hydrochloric acid, it takes time to dissolve. But if we crush it into powder, it disappears quickly.
Why does this happen?
- Smaller particles (powder) have more surface area for the acid to react with.
- This allows the reaction to happen faster.
- Large pieces have less surface area, so the reaction is slow.
Example:
Just like sugar cubes dissolve slowly in water but powdered sugar dissolves quickly, crushed Shahabad tile reacts faster in HCl than a solid piece.
Give scientific reason:
While preparing dilute sulphuric acid from concentrated sulphuric acid in the laboratory, the concentrated sulphuric acid is added slowly to water with constant stirring.
Scientific and Written Exam Answer:
Concentrated sulphuric acid (H₂SO₄) has a very high affinity for water and releases a large amount of heat when mixed with it. This process is highly exothermic:
$$ H_2SO_4 + H_2O \rightarrow H_3O^+ + HSO_4^- + \text{heat} $$Precaution: To avoid splashing or explosion, concentrated H₂SO₄ must be added slowly to water with continuous stirring.
Explanation:
- If water is added to concentrated acid, the sudden heat generated can cause the water to boil instantly.
- This may lead to the acid splashing, causing severe burns.
- By adding acid to water gradually, the heat is dissipated slowly and safely.
Simple and Understandable Answer:
When we mix concentrated sulphuric acid with water, it produces a lot of heat.
Why is acid added to water and not the other way around?
- Adding water to acid suddenly produces extreme heat, which can make the acid splash.
- This can cause burns and accidents.
- Adding acid to water slowly with stirring keeps the reaction under control.
Example:
Imagine pouring water into hot oil—it splashes dangerously. Similarly, adding water to acid causes a violent reaction, so we add acid to water slowly.
Give scientific reason:
It is recommended to use an airtight container for storing oil for a long time.
Scientific and Written Exam Answer:
Oils contain unsaturated fatty acids, which react with oxygen in the air in a process called oxidation. This leads to the formation of peroxides, which cause the oil to become rancid.
$$ \text{Unsaturated Fat} + O_2 \rightarrow \text{Peroxides (rancid smell)} $$Why Airtight Containers?
- Prevent contact with oxygen, slowing down oxidation.
- Protect oil from moisture, which can accelerate spoilage.
- Maintain the taste, smell, and quality of oil for a long time.
Simple and Understandable Answer:
Oil can spoil when exposed to air because it reacts with oxygen and develops a bad smell (rancidity).
Why store oil in an airtight container?
- Stops oxygen from reacting with oil and spoiling it.
- Prevents the formation of a bad smell.
- Keeps oil fresh and usable for a long time.
Example:
Have you ever noticed that chips in an open packet taste stale after a few days? This happens because the oil in them reacts with air. Sealing oil in an airtight container prevents this.
Observe the following picture and write down the chemical reaction with the explanation.
Scientific and Written Exam Answer:
The rusting of iron is an oxidation process. It does not occur by a simple reaction between oxygen and iron but through an electrochemical reaction. Different parts of the iron surface act as anode and cathode, leading to rust formation.
Electrochemical Reactions:
1) Oxidation at Anode: Iron loses electrons and forms Fe2+ ions.
$$ Fe(s) \rightarrow Fe^{2+}(aq) + 2e^- $$2) Reduction at Cathode: Oxygen from the air reacts with H+ ions and electrons to form water.
$$ O_2(g) + 4H^+(aq) + 4e^- \rightarrow 2H_2O(l) $$3) Formation of Rust: The Fe2+ ions further react with water and oxygen, forming Fe3+ ions, which combine with water to form reddish-brown rust (hydrated ferric oxide).
$$ 2Fe^{3+}(aq) + 4H_2O(l) \rightarrow Fe_2O_3 \cdot xH_2O(s) + 6H^+(aq) $$Concept of Corrosion:
- Corrosion is the slow deterioration of metals due to oxidation.
- Rusting of iron is a common example of corrosion.
- Exposure to moisture and oxygen accelerates rust formation.
Simple and Understandable Answer:
When iron is exposed to air and moisture for a long time, it forms a reddish-brown substance called rust. This happens because iron reacts with oxygen and water in the air.
Why Does Rusting Happen?
- Iron reacts with oxygen and water.
- A new substance called rust (Fe2O3.xH2O) is formed.
- Rust makes iron weak and brittle.
Example:
If you leave an iron nail outside in the rain, you will see a brown layer forming on it. That is rust! This process is called corrosion.
Identify from the reaction the reactants that undergo oxidation and reduction.
Reaction:
$$ Fe + S \rightarrow FeS $$
Scientific and Written Exam Answer:
Oxidation: Iron (Fe) undergoes oxidation because it loses electrons and forms Fe²⁺ ions in iron sulfide (FeS).
Reduction: Sulfur (S) undergoes reduction because it gains electrons and forms S²⁻ ions.
Explanation:
Oxidation refers to the loss of electrons, while reduction refers to the gain of electrons. In this reaction, iron donates electrons to sulfur, resulting in the formation of iron sulfide (FeS).
Identify from the following reaction the reactants that undergo oxidation and reduction.
Reaction:
$$ 2Ag_2O \rightarrow 4Ag + O_2 \uparrow $$
Scientific and Written Exam Answer:
Oxidation: Oxygen (O²⁻) in silver oxide (Ag₂O) undergoes oxidation as it loses electrons and forms oxygen gas (O₂).
Reduction: Silver ions (Ag⁺) in silver oxide undergo reduction as they gain electrons and form pure silver (Ag).
Explanation:
This is an example of a thermal decomposition reaction, where silver oxide (Ag₂O) decomposes into silver metal (Ag) and oxygen gas (O₂) when heated.
Oxygen undergoes oxidation (loses electrons), and silver undergoes reduction (gains electrons).
Identify from the reaction the reactants that undergo oxidation and reduction.
Reaction:
$$ 2Mg + O_2 \rightarrow 2MgO $$
Scientific and Written Exam Answer:
Oxidation: Magnesium (Mg) undergoes oxidation as it loses electrons and forms magnesium ions (Mg²⁺).
Reduction: Oxygen (O₂) undergoes reduction as it gains electrons and forms oxide ions (O²⁻).
Explanation:
Oxidation is the loss of electrons, while reduction is the gain of electrons. In this reaction, magnesium atoms donate electrons to oxygen molecules, resulting in the formation of magnesium oxide (MgO).
Identify from the reaction the reactants that undergo oxidation and reduction.
Reaction:
$$ NiO + H_2 \rightarrow Ni + H_2O $$
Scientific and Written Exam Answer:
Oxidation: Hydrogen (H₂) undergoes oxidation as it loses electrons and forms hydrogen ions (H⁺) in water (H₂O).
Reduction: Nickel oxide (NiO) undergoes reduction as Ni²⁺ ions gain electrons and form nickel (Ni).
Explanation:
In this reaction, hydrogen acts as a reducing agent, removing oxygen from nickel oxide, converting it into nickel metal (Ni).
This is a classic example of a reduction-oxidation (redox) reaction, where one substance undergoes oxidation (loses electrons) and the other undergoes reduction (gains electrons).
Balance the equation stepwise.
Unbalanced chemical equation:
H2S2O7(l) + H2O(l) → H2SO4(l)
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
Reactants: H2S2O7 (Pyrosulfuric acid) and H2O (Water)
Products: H2SO4 (Sulfuric acid)
Step 2: Count the number of atoms on both sides
| Element | Reactants | Products |
|---|---|---|
| H | 4 | 2 |
| S | 2 | 1 |
| O | 8 | 4 |
Step 3: Adjust the coefficients to balance atoms
Since we have two sulfur atoms on the reactant side and only one on the product side, we must adjust the coefficient:
H2S2O7(l) + H2O(l) → 2 H2SO4(l)
Step 4: Verify the balance
| Element | Reactants | Products |
|---|---|---|
| H | 4 | 4 |
| S | 2 | 2 |
| O | 8 | 8 |
The equation is now balanced.
Balance the equation stepwise:
Unbalanced equation:
SO2(g) + H2S(aq) → S(s) + H2O(l)
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactants: Sulfur dioxide (SO2), Hydrogen sulfide (H2S)
- Products: Sulfur (S), Water (H2O)
Step 2: Count the number of atoms on both sides
| Element | Reactant Side | Product Side |
|---|---|---|
| Sulfur (S) | 2 (1 from SO2, 1 from H2S) | 1 |
| Oxygen (O) | 2 | 1 |
| Hydrogen (H) | 2 | 2 |
Step 3: Adjust the coefficients to balance the equation
- Sulfur atoms are unbalanced; we need 3 S atoms on the right side.
- To balance sulfur, adjust the coefficient of H2S:
SO2 + 2H2S → 3S + H2O
- Now, balance oxygen by adjusting H2O molecules:
SO2 + 2H2S → 3S + 2H2O
Step 4: Verify the balance
| Element | Reactant Side | Product Side |
|---|---|---|
| Sulfur (S) | 3 | 3 |
| Oxygen (O) | 2 | 2 |
| Hydrogen (H) | 4 | 4 |
Final Balanced Equation:
$$ SO_2(g) + 2H_2S(aq) → 3S(s) + 2H_2O(l) $$
Simple and Understandable Answer:
To balance this reaction:
- Count the number of atoms on both sides.
- Adjust the sulfur atoms first.
- Next, balance oxygen and hydrogen atoms.
The final balanced equation is:
SO2 + 2H2S → 3S + 2H2O
Example: This reaction is an example of a redox reaction where SO2 is reduced and H2S is oxidized.
Balance the equation stepwise:
Unbalanced equation:
Ag(s) + HCl(aq) → AgCl ↓ + H2 ↑
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactants: Silver (Ag), Hydrochloric acid (HCl)
- Products: Silver chloride (AgCl), Hydrogen gas (H2)
Step 2: Count the number of atoms on both sides
| Element | Reactant Side | Product Side |
|---|---|---|
| Silver (Ag) | 1 | 1 |
| Hydrogen (H) | 1 | 2 |
| Chlorine (Cl) | 1 | 1 |
Step 3: Adjust the coefficients to balance the equation
- The hydrogen atoms are unbalanced. On the reactant side, we have one H atom from HCl, but on the product side, hydrogen exists as H2 (a diatomic molecule).
- To balance hydrogen, we need 2 HCl molecules:
Ag(s) + 2HCl(aq) → AgCl ↓ + H2 ↑
Step 4: Verify the balance
| Element | Reactant Side | Product Side |
|---|---|---|
| Silver (Ag) | 1 | 1 |
| Hydrogen (H) | 2 | 2 |
| Chlorine (Cl) | 2 | 2 |
Final Balanced Equation:
$$ Ag(s) + 2HCl(aq) → AgCl(s) ↓ + H_2(g) ↑ $$
Simple and Understandable Answer:
To balance this reaction:
- Count the number of atoms on both sides.
- Notice that hydrogen needs to be balanced.
- Add 2 HCl molecules to balance hydrogen and chlorine.
The final balanced equation is:
Ag + 2HCl → AgCl + H2
Example: This reaction shows how silver reacts with hydrochloric acid to form silver chloride and hydrogen gas.
Balance the equation stepwise:
Unbalanced equation:
NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l)
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactants: Sodium hydroxide (NaOH), Sulfuric acid (H2SO4)
- Products: Sodium sulfate (Na2SO4), Water (H2O)
Step 2: Count the number of atoms on both sides
| Element | Reactant Side | Product Side |
|---|---|---|
| Sodium (Na) | 1 | 2 |
| Hydrogen (H) | 3 | 2 |
| Sulfur (S) | 1 | 1 |
| Oxygen (O) | 5 | 5 |
Step 3: Adjust the coefficients to balance the equation
- Sodium (Na) atoms are unbalanced. On the left, there is 1 Na atom, while on the right, there are 2 Na atoms in Na2SO4.
- To balance Na, multiply NaOH by 2:
$$ 2NaOH(aq) + H_2SO_4(aq) → Na_2SO_4(aq) + H_2O(l) $$
Step 4: Verify the balance
| Element | Reactant Side | Product Side |
|---|---|---|
| Sodium (Na) | 2 | 2 |
| Hydrogen (H) | 4 | 4 |
| Sulfur (S) | 1 | 1 |
| Oxygen (O) | 6 | 6 |
Final Balanced Equation:
$$ 2NaOH(aq) + H_2SO_4(aq) → Na_2SO_4(aq) + 2H_2O(l) $$
Simple and Understandable Answer:
To balance this reaction:
- Count the number of atoms on both sides.
- Notice that sodium is unbalanced.
- Add 2 NaOH molecules to balance sodium.
The final balanced equation is:
2NaOH + H2SO4 → Na2SO4 + 2H2O
Example: This reaction represents the neutralization of sulfuric acid by sodium hydroxide, forming sodium sulfate and water.
Identify the endothermic and exothermic reaction:
Given reaction:
HCl + NaOH → NaCl + H2O + heat
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactants: Hydrochloric acid (HCl), Sodium hydroxide (NaOH)
- Products: Sodium chloride (NaCl), Water (H2O), Heat
Step 2: Define exothermic and endothermic reactions
- Exothermic reaction: A reaction that releases heat energy.
- Endothermic reaction: A reaction that absorbs heat energy.
Step 3: Identify the reaction type
- The reaction releases heat, which means it is an exothermic reaction.
- Exothermic reactions give off energy in the form of heat or light.
Step 4: Final Conclusion
Since the reaction releases heat, it is classified as an exothermic reaction.
Simple and Understandable Answer:
This reaction is a neutralization reaction where hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form salt (NaCl) and water (H2O).
- When acid and base react, they release heat.
- Since heat is released, this is called an exothermic reaction.
Example: When you mix acid and base in a beaker, you can feel the beaker getting warm. This is because the reaction gives off heat.
Identify the endothermic and exothermic reaction:
Given reaction:
2 KClO3 (s) → Δ 2 KCl (s) + 3 O2 (g)
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactant: Potassium chlorate (KClO3)
- Products: Potassium chloride (KCl), Oxygen gas (O2)
Step 2: Identify the heat transfer
- The reaction requires heat (Δ) to break down KClO3 into KCl and O2.
Step 3: Identify the reaction type
- Since heat is absorbed, this is an endothermic reaction.
Simple and Understandable Answer:
In this reaction, potassium chlorate breaks down when heated.
- This process absorbs heat, so it is an endothermic reaction.
Example: Heating potassium chlorate in a test tube causes it to break down and release oxygen gas.
Identify the endothermic and exothermic reaction:
Given reaction:
CaO + H2O → Ca(OH)2 + Heat
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactants: Calcium oxide (CaO), Water (H2O)
- Product: Calcium hydroxide (Ca(OH)2), Heat
Step 2: Identify the reaction type
- Since heat is released, this is an exothermic reaction.
Simple and Understandable Answer:
When calcium oxide (quicklime) is mixed with water, heat is released.
- This reaction is called slaking of lime.
- Since heat is given off, it is an exothermic reaction.
Example: If you mix quicklime with water, the container gets hot.
Identify the endothermic and exothermic reaction:
Given reaction:
CaCO3 (s) → Δ CaO (s) + CO2 (g)
Scientific and Written Exam Answer:
Step 1: Identify the reactants and products
- Reactant: Calcium carbonate (CaCO3)
- Products: Calcium oxide (CaO), Carbon dioxide (CO2)
Step 2: Identify the reaction type
- Since heat (Δ) is required for the reaction, it is an endothermic reaction.
Simple and Understandable Answer:
When calcium carbonate is heated, it breaks down into calcium oxide and carbon dioxide gas.
- Since heat is absorbed to make this happen, it is an endothermic reaction.
Example: Heating limestone (CaCO3) in a kiln produces quicklime (CaO).
Identify the type of chemical reaction for each reaction given below.
| Reactants | Products | Type of Chemical Reaction |
|---|---|---|
| BaCl₂(aq) + ZnSO₄(aq) | H₂CO₃(aq) | Displacement |
| 2AgCl(s) | FeSO₄(aq) + Cu(s) | Combination |
| CuSO₄(aq) + Fe(s) | BaSO₄↓ + ZnCl₂(aq) | Decomposition |
| H₂O(l) + CO₂(g) | 2Ag(s) + Cl₂(g) | Double displacement |
Solution: Identify the type of chemical reaction for each reaction.
| Reactants | Products | Type of Chemical Reaction |
|---|---|---|
| BaCl₂(aq) + ZnSO₄(aq) | BaSO₄↓ + ZnCl₂(aq) | Double Displacement Reaction |
| 2AgCl(s) | 2Ag(s) + Cl₂(g) | Decomposition Reaction |
| CuSO₄(aq) + Fe(s) | FeSO₄(aq) + Cu(s) | Displacement Reaction |
| H₂O(l) + CO₂(g) | H₂CO₃(aq) | Combination Reaction |
Explanation:
- Double Displacement Reaction: In this reaction, two compounds exchange their ions to form new compounds. Here, BaCl₂ and ZnSO₄ react to form BaSO₄ (precipitate) and ZnCl₂.
- Decomposition Reaction: A single compound breaks down into two or more simpler substances. AgCl decomposes into silver (Ag) and chlorine (Cl₂) gas.
- Displacement Reaction: A more reactive metal displaces a less reactive metal from its compound. Iron (Fe) displaces copper (Cu) from CuSO₄ to form FeSO₄.
- Combination Reaction: Two or more reactants combine to form a single product. Water (H₂O) and carbon dioxide (CO₂) combine to form carbonic acid (H₂CO₃).