Class 10 Chapter 2 Acids, Bases and Salt

Key Concept: Complex Reaction Analysis, Real-world Application

b) 98.09 g
[Solution Description] The balanced chemical equation for the reaction is:

$\text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{CO}_2 + \text{H}_2\text{O}$

The molar mass of $\text{CaCO}_3$ is $40.08 + 12.01 + 3 \times 16.00 = 100.09 \, \text{g/mol}$.

Hence, moles of $\text{CaCO}_3$ used are:$\frac{100 \, \text{g}}{100.09 \, \text{g/mol}} \approx 1.00 \, \text{mol}$

From the stoichiometry of the reaction (1:1), moles of $\text{H}_2\text{SO}_4$ required are also $1.00 \, \text{mol}$.

The molar mass of $\text{H}_2\text{SO}_4$ is $2 \times 1.01 + 32.07 + 4 \times 16.00 = 98.09 \, \text{g/mol}$.

Therefore, the mass of $\text{H}_2\text{SO}_4$ neutralized is:$1.00 \, \text{mol} \times 98.09 \, \text{g/mol} = 98.09 \, \text{g}$

Notes:

• Complex Reactions: Reactions involving multiple steps, where products from one stage act as reactants for another.
• Example: Neutralization reaction (acid + base → salt + water), which can involve complex interactions, especially in buffer solutions.
• Real-World Applications:
  • Antacid Tablets: Contain bases to neutralize stomach acid.
  • Soil Treatment: Lime (a base) is used to neutralize acidic soils for better crop growth.
  • Titration: Used in laboratories to determine the concentration of an acid or base in a solution.
• Biological Processes: Blood pH regulation involves complex acid-base reactions to maintain homeostasis.

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Key Concept: pH Classification

b) Acidic
[Solution Description] Hydrochloric acid is a strong acid and ammonia is a weak base. The salt formed will be ammonium chloride $(NH_4Cl)$, which is acidic in nature.

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Key Concept: pH Identification

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that salts formed from a strong base and a weak acid are basic. This is true because the strong base dominates over the weak acid, resulting in a salt solution with basic properties. The reason provided explains that these salts have a pH value greater than 7, which aligns with the definition of a basic substance having a pH above 7. Therefore, both the Assertion and Reason are true, and the Reason correctly explains why the Assertion is true.

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Key Concept: Salt Formation

c) Potassium nitrate
[Solution Description] The reaction between nitric acid $(HNO_3)$ and potassium hydroxide (KOH) follows the equation:
$\text{HNO}_3 + \text{KOH} \rightarrow \text{KNO}_3 + \text{H}_2\text{O}$
Therefore, the salt formed is potassium nitrate.

Key Concept: Salt Family Classification, Industrial Salt Process

c) Direct combination; Sulfate family
[Solution Description]
Magnesium sulfate can be prepared by reacting sulfuric acid $(H_2SO_4)$ with magnesium oxide MgO:$MgO + H_2SO_4 \rightarrow MgSO_4 + H_2O$
Magnesium sulfate is part of the sulfate family due to its anion $(SO_4^{2-})$. This compound is also known as Epsom salt and is used in various industries, including agriculture and pharmaceuticals.

Notes:

• Salt Family Classification:
  • Normal Salts: Formed by neutralization of acids and bases (e.g., NaCl).
  • Acidic Salts: Formed when a strong acid reacts with a weak base (e.g., NH4Cl).
  • Basic Salts: Formed when a weak acid reacts with a strong base (e.g., Na2CO3).
  • Double Salts: Composed of two different salts (e.g., K2SO4·Al2(SO4)3).
• Industrial Salt Process:
  • Rock Salt Mining: Extracted from underground salt mines.
  • Solar Evaporation: Seawater evaporated in shallow ponds to produce salt.
  • Vacuum Evaporation: Boiling seawater in vacuum chambers to produce purified salt.
  • Uses: In food industry, de-icing, and chemical production.

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Key Concept: Salt Uses

a) Making cement
[Solution Description] Calcium sulphate, commonly known as gypsum, is widely used in the construction industry for making plaster and drywall. It’s not typically used for antacids, fertilizers, or explosives.

Notes:

Key Concept: Salt Families

a) $\text{KCl}$
[Solution Description] Chloride salts include any salt where the anion is $\text{Cl}^-$. Looking at each option, a), c), and d) contain $\text{Cl}^-$ ions, but KCl specifically fits the chloride salt category.

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Key Concept: Salt Reaction Prediction, Real-world Salt Application

c) Barium sulfate and ammonium chloride; Used in X-ray imaging
[Solution Description]
To predict the products, we first write the balanced equation for the double displacement reaction:$(NH_4)_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NH_4Cl$
Barium sulfate $(BaSO_4)$ is an insoluble salt that precipitates out, and ammonium chloride $(NH_4Cl)$ remains in solution. Such precipitation reactions are used to remove unwanted ions from solutions or to purify substances. In medical applications, barium sulfate is used as a radiocontrast agent for X-ray imaging.

Notes:

Key Concept: Neutralization Reaction Analysis, Salt pH Analysis

c) Ammonium nitrate; it makes the solution slightly acidic.
[Solution Description] Nitric acid $(\text{HNO}_3)$ is a strong acid, while ammonium hydroxide $(\text{NH}_4\text{OH})$ is a weak base. The reaction forms ammonium nitrate $(\text{NH}_4\text{NO}_3)$:$\text{HNO}_3 + \text{NH}_4\text{OH} \rightarrow \text{NH}_4\text{NO}_3 + \text{H}_2\text{O}$
Due to the strong acid and weak base, the salt will be slightly acidic and will lower the pH below 7.

Notes:

Neutralization Reaction

• A neutralization reaction occurs when an acid reacts with a base to form water and a salt.
• Example:
  HCl+NaOH→NaCl+H2OHCl + NaOH .
• The acidic and basic properties cancel each other out, resulting in a neutral solution (pH = 7).
• This reaction is exothermic, releasing heat.

Salt pH Analysis

• Salts formed in neutralization reactions can have different pH values based on the strength of the acid and base used.
  • Neutral Salts: Formed by strong acid + strong base (e.g., NaCl, KNO₃), pH = 7.
  • Acidic Salts: Formed by strong acid + weak base (e.g., NH₄Cl), pH < 7.
  • Basic Salts: Formed by weak acid + strong base (e.g., Na₂CO₃), pH > 7.

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Key Concept: Salt Family

a) Chloride salts
[Solution Description] Calcium chloride $(CaCl_2)$ is composed of calcium ions $(Ca^{2+})$ and chloride ions $(Cl^-)$. It can be classified under both calcium salts and chloride salts as it contains both ions. However, according to standard classification based on anions, it belongs to the chloride family.

Notes:

• Definition: Salts are ionic compounds formed by the neutralization of acids with bases.
• Types of Salts:
  1. Normal salts: Formed from strong acid and strong base (e.g., NaCl).
  2. Acid salts: Formed from a weak acid and a strong base (e.g., NaHSO₄).
  3. Basic salts: Formed from a weak base and a strong acid (e.g., Al(OH)₂Cl).
  4. Double salts: Formed by two different salts crystallizing together (e.g., Mohr’s salt).
• Uses: Salts are used in food preservation, in the manufacturing of soaps, and in industries.
• Common Examples: Sodium chloride (NaCl), potassium nitrate (KNO₃), copper sulfate (CuSO₄).

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Key Concept: Neutralization Reaction

d) Sodium chloride $(NaCl)$
[Solution Description] The neutralization reaction involves a strong acid (HCl) reacting with a strong base (NaOH). The general reaction for neutralization is:
$H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$
For this specific case, we have:$HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$
Hence, sodium chloride (NaCl) is the salt formed.

Notes:

• Definition: A neutralization reaction occurs when an acid reacts with a base to form water and a salt.
• General Equation:
  Acid + Base → Salt + Water
• Example:
  HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water)
• Characteristics:
  • Heat is usually released in the reaction (exothermic).
  • pH of the solution becomes neutral (pH = 7).
• Applications:
  • Used in antacids to neutralize excess stomach acid.
  • Lime (CaO) is used to neutralize acidic soil.
• Important Note: Neutralization can be complete or partial depending on the strength of acid/base.

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Key Concept: Salt Family Identification

b) Nitrate salts
[Solution Description] $\text{KNO}_{3}$ (potassium nitrate) and $\text{NaNO}_{3}$ (sodium nitrate) both share the common negative radical $\text{NO}_3^-$, so they belong to the nitrate family of salts.

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Key Concept: Reaction Conditions

c) Electricity
[Solution Description]
The chlor-alkali process involves the electrolysis of an aqueous solution of sodium chloride NaCl. During this process, electricity is used to decompose the salt into sodium hydroxide NaOH, chlorine gas $(Cl_2)$, and hydrogen gas $(H_2)$. Therefore, electricity is the necessary condition.

Notes:

• Acid-Base Reactions: Occur when an acid reacts with a base to form salt and water.
• Neutralization: The process where an acid neutralizes a base, forming salt and water.
• Temperature: Some reactions are temperature-dependent, such as the dissolution of salts.
• Concentration: The concentration of reactants affects the rate and outcome of reactions.
• Catalysts: May be required to speed up reactions without being consumed.
• Indicators: Used to identify the nature of substances (acidic or basic).
• Dilution: Reduces the reactivity of acids or bases when diluted with water.

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Key Concept: Industrial Process Understanding, Complex Reaction Pathways

c) $NaCl \rightarrow NaHCO_3 \rightarrow Na_2CO_3 \rightarrow Na_2CO_3.10H_2O$
[Solution Description] The production of washing soda from common salt follows: $NaCl \rightarrow NaHCO_3 \rightarrow Na_2CO_3 \rightarrow Na_2CO_3.10H_2O$. This includes initial conversion to sodium bicarbonate and then to sodium carbonate before recrystallization into washing soda.

Notes:

Key Concept: Product Properties

d) It is alkaline
[Solution Description]
Washing soda, or sodium carbonate decahydrate $\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$, is known for being alkaline and is commonly used in cleaning and softening water. It’s not acidic or neutral but rather acts as a strong base.

Notes:

• Acidic Products:
  • Acids release hydrogen ions (H⁺) in water.
  • They have a sour taste (e.g., vinegar, lemon juice).
  • Turn blue litmus paper red.
  • Examples: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄).
• Basic Products:
  • Bases release hydroxide ions (OH⁻) in water.
  • They have a bitter taste and slippery feel.
  • Turn red litmus paper blue.
  • Examples: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂).
• Salt Formation:
  • Neutralization reaction between acid and base forms salts and water.
  • Example: NaOH + HCl → NaCl (salt) + H₂O.
• Properties of Salts:
  • Salts are neutral, conduct electricity in molten or dissolved form.
  • Example: Sodium chloride (NaCl), Copper sulfate (CuSO₄).

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Key Concept: Chlor-Alkali Process Application, Industrial Process Understanding

c) Sodium hydroxide $(NaOH)$
[Solution Description] The chlor-alkali process produces sodium hydroxide (NaOH), chlorine $(Cl_2)$, and hydrogen gas $(H_2)$. Sodium hydroxide is an essential compound used to regulate pH levels in various industrial processes due to its strong basic nature.

Notes:

• Chlor-Alkali Process is an industrial method used to produce chlorine (Cl₂), sodium hydroxide (NaOH), and hydrogen (H₂) from the electrolysis of brine (sodium chloride solution).
• Electrolysis of Brine: When electric current passes through brine, chlorine gas forms at the anode, hydrogen gas at the cathode, and sodium hydroxide remains in the solution.
• Applications:
  • Chlorine: Used in disinfectants, PVC plastic, and water purification.
  • Sodium Hydroxide: Used in soap-making, paper production, and textile industries.
  • Hydrogen: Used in hydrogenation of oils and in fuel cells.
• Industrial Importance: Vital for producing chemicals used in various industries like textiles, plastics, and detergents.

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Key Concept: In-depth Analysis, Advanced Chemical Understanding

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] Upon heating, gypsum $(CaSO_4.2H_2O)$ loses its water of crystallization and forms anhydrite $(CaSO_4)$. Anhydrite is indeed more thermally stable compared to plaster of Paris, as it withstands higher temperatures without significant structural changes. On the other hand, plaster of Paris, formed by partial dehydration of gypsum, can absorb moisture to revert to gypsum. Therefore, while both statements are true, the ability of plaster of Paris to reabsorb water does not explain why anhydrite is more stable at elevated temperatures. Hence, the reason is not the correct explanation of the assertion.

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Key Concept: Problem Solving, Critical Thinking

c) 36%
[Solution Description]
Determine the mass of the water lost:$\text{Water lost} = 25 – 16 = 9 \text{ grams}$
Then calculate the percentage of water:$\text{Percentage of Water} = \left(\frac{9}{25}\right) \times 100\% = 36\%$

Notes:

• Problem Solving: Involves identifying a problem, analyzing it, and finding a solution using logical steps.
• Critical Thinking: The ability to think clearly, logically, and objectively. It helps in evaluating information and arguments.
• Steps in Problem Solving:
  • Understanding the problem.
  • Breaking it into smaller parts.
  • Analyzing the components.
  • Testing possible solutions.
  • Reaching a conclusion.
• Importance of Critical Thinking: Helps in making informed decisions, avoiding biases, and solving complex problems effectively.
• Applications: Used in scientific experiments, real-life situations, and daily decision-making processes.

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Key Concept: Process Explanation

b) Dehydration
[Solution Description] The removal of water from crystalline salts by heating is known as dehydration. This process alters the physical properties of the salt such as color change observed in copper sulphate.

Notes:

Process Explanation:

1. Acid-Base Reaction (Neutralization):
   • When an acid reacts with a base, it forms water and salt.
   • Example: HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water).
2. Formation of Salts:
   • Salts are formed when an acid reacts with a base, or when an acid reacts with a metal.
   • Example: HCl + NaOH → NaCl + H₂O.
3. Titration Process:
   • It is a method to determine the concentration of an acid or base by using a neutralization reaction.
   • A known concentration of base (NaOH) is used to neutralize an unknown acid (HCl) and the amount of base used helps calculate the concentration of the acid.
4. Importance of Indicators:
   • Indicators such as litmus paper, phenolphthalein, or methyl orange are used to identify whether a substance is acidic or basic.

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Key Concept: Critical Thinking, Advanced Application

d) They help stabilize active ingredients in formulations.
[Solution Description]
Compounds with water of crystallization often stabilize active ingredients, which helps maintain drug efficacy and shelf life.

Notes:

• Critical Thinking involves analyzing, evaluating, and synthesizing information to form reasoned judgments.
• It is essential in solving complex problems, making decisions, and drawing conclusions based on evidence.
• Key skills:
  • Questioning assumptions
  • Identifying biases
  • Evaluating evidence
  • Recognizing patterns and inconsistencies
• In scientific research, critical thinking helps in formulating hypotheses, designing experiments, and interpreting results.
• Advanced Applications of critical thinking are seen in:
  • Innovative technology development
  • Medical advancements like new treatments
  • Environmental solutions to global challenges.
• It aids in adapting to new information and evolving understanding in various fields.

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Key Concept: Reaction Equation

a) $CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$
[Solution Description] When Plaster of Paris, which is calcium sulphate hemihydrate $(CaSO_4 \cdot \frac{1}{2}H_2O)$, is mixed with water, it forms gypsum $(CaSO_4 \cdot 2H_2O)$. The chemical equation for this reaction is:$CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$

Thus, option a) is correct.

Notes:

• Chemical Reaction: A process where reactants are transformed into products, with a change in energy.
• Reactants & Products: Substances before and after the reaction, respectively.
• Chemical Equation: A symbolic representation of a chemical reaction using formulas (e.g.,
  A+B→C+DA + B.
• Balancing Equations: Atoms of each element must be the same on both sides.
• Types of Reactions:
  • Combination: Two or more reactants combine (e.g.,
    A+B→ABA + B .
  • Decomposition: A compound breaks into simpler products (e.g.,
    AB→A+BAB .
  • Displacement: One element replaces another in a compound.
  • Double Displacement: Two compounds exchange ions.

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Key Concept: Material Property

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] The assertion discusses the property of Plaster of Paris as a white powder useful for smoothing surfaces, which is a correct statement. The reason mentions its usage in decoration and medical support, both of which are true. However, the reason does not directly explain why it is suitable for making surfaces smooth. Thus, while both statements are true, the reason is not the direct explanation of the assertion.

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Key Concept: Comparative Analysis, Conceptual Understanding

b) Gypsum has more water of crystallization than Plaster of Paris
[Solution Description] Gypsum $(CaSO_4 \cdot 2H_2O)$ contains more water of crystallization compared to Plaster of Paris $(CaSO_4 \cdot \frac{1}{2}H_2O)$. This gives gypsum a slightly different structural property compared to Plaster of Paris and makes it unsuitable for some applications where rapid setting is required.

Notes:

Key Concept: Industrial Application

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion that “Plaster of Paris is extensively used in making casts for setting broken bones” is true since its ability to form a hard, solid mass upon mixing with water makes it ideal for supporting and immobilizing broken bones. The reason given that “Plaster of Paris cannot be easily molded into desired shapes or forms” is false because one of the principal advantages of Plaster of Paris is its ease of molding when mixed with water before it hardens. This allows it to accurately conform to the shape needed, such as a limb needing support. Therefore, the correct response is (c).

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Key Concept: Indicator Use

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion is about phenolphthalein, which indeed changes color in basic solutions indicating its role as a synthetic indicator – this statement is true. The reason states that a solution with pH 8 will turn blue litmus paper red. However, a solution with pH 8 is considered basic and would actually keep blue litmus paper unchanged while turning red litmus paper blue. Therefore, the reason provided is false.

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Key Concept: Conductivity in Solutions

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion is that acidic solutions can conduct electricity. This is true because when acids dissolve in water, they dissociate to release hydrogen ions $(H^+)$ and other anions, which facilitate the conduction of electricity through the solution.

The reason given is that acids dissociate into ions when mixed with water, which is also true. It explains why the conductivity happens; therefore, the reason supports the assertion.

Since both the assertion and the reason are true, and the reason correctly explains the assertion by providing a cause for the conductivity, option (a) is correct.

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Key Concept: Hydrogen Ion Production, Dilution Effects

b) 0.7

[Solution Description]

First calculate the initial concentration of $\text{H}^+$ ions before dilution using $c_1v_1 = c_2v_2$ where $c_1$ is the initial concentration and $v_1$ the initial volume:

$1 \times 100 = c_2 \times 500$

Solving for $c_2$:

$c_2 = \frac{100}{500} = 0.2 \, \text{M}$

The $\text{pH}$ is given by:

$\text{pH} = -\log_{10}(c_2)$

Calculate:

$\text{pH} = -\log_{10}(0.2) = 0.69897 \approx 0.7$

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Key Concept: Real-world Application, Effect of Dilution

c) Assertion is true, but Reason is false.

[Solution Description] Baking soda, or sodium bicarbonate $(\text{NaHCO}_3),$ reacts with acids present in doughs or batters to neutralize them, producing carbon dioxide which helps baked goods rise. This makes Assertion true as it correctly describes a real-world application of baking soda. However, when you dilute an alkaline solution, the concentration of hydroxide ions decreases, which leads to a decrease in pH rather than an increase, making the Reason false.

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Key Concept: Basic Properties

b) Bitter

[Solution Description] Bases typically have a bitter taste. This is one of the fundamental characteristics of basic substances.

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Key Concept: pH Identification

c) Lemon juice

[Solution Description]

The pH scale measures how acidic or basic a solution is, with values below 7 indicating acidity. Among the options given:

– Lemon juice is known as an acidic substance.

– Detergent solution and baking soda are typically basic.

– Pure water is neutral.

Thus, lemon juice has a pH less than 7.

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Key Concept: Hydronium Ion Formation, Real-world Application

b) Hydronium ion formation leads to the evolution of carbon dioxide gas.

[Solution Description]

The reaction between citric acid in lemon juice and sodium bicarbonate is a typical acid-base reaction where citric acid donates protons to the bicarbonate ions, forming water and carbon dioxide gas, which is responsible for the effervescence observed. The crucial part of this reaction is the formation of $\text{H}_3\text{O}^+$ ions when the acid dissolves in water, which then participates in forming $\text{CO}_2$ gas:

$\text{C}_6\text{H}_8\text{O}_7 + 3\text{NaHCO}_3 \rightarrow 3\text{CO}_2 + 3\text{H}_2\text{O} + \text{Na}_3\text{C}_6\text{H}_5\text{O}_7$

Here, the hydronium ions ($\text{H}_3\text{O}^+$) formed by citric acid are directly involved in the reaction process.

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Key Concept: Neutralization Reaction

c) Salt, water, and carbon dioxide

[Solution Description] When an acid reacts with a metal carbonate, it produces a salt, water, and carbon dioxide gas. This reaction is a typical characteristic of acids reacting with carbonates.

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Key Concept: Gas Identification

b) Hydrogen

[Solution Description]

Zinc $(\text{Zn})$ reacts with sodium hydroxide $(\text{NaOH})$ to produce sodium zincate $(\text{Na}_2\text{ZnO}_2)$ and hydrogen gas $(\text{H}_2)$. The reaction is:

$2\text{NaOH} + \text{Zn} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2$

Therefore, hydrogen gas is evolved during this reaction.

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Key Concept: Reaction Mechanism, Reaction Application

b) Zinc oxide forms water-soluble zinc sulfate and water.

[Solution Description]

The reaction between zinc oxide and sulfuric acid follows the equation:

$\text{ZnO} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O}$

The mechanism involves protonation from the sulfuric acid to convert ZnO into soluble zinc sulfate while releasing water. This reaction is favored in industry because it efficiently converts insoluble zinc compounds into valuable zinc sulfate, used widely as a dietary supplement and in agriculture.

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Key Concept: Reaction Conditions

a) At room temperature

[Solution Description]

Magnesium reacts with hydrochloric acid under normal conditions to form magnesium chloride and hydrogen gas. The reaction happens readily at room temperature without the need for heating or pressure. The balanced chemical equation is:

$\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$

No special condition like heating is required for this reaction to proceed.

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Key Concept: Basic Reaction

b) Salt and hydrogen gas

[Solution Description]

When hydrochloric acid $(\text{HCl})$ reacts with magnesium $(\text{Mg})$, it forms magnesium chloride $(\text{MgCl}_2)$ and hydrogen gas $(\text{H}_2)$. The reaction is represented as:

$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$

So, the products are salt (magnesium chloride) and hydrogen gas.

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Key Concept: Ion Formation

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion is true because when acids are dissolved in water, they dissociate to produce hydrogen ions $(H^+),$ which are responsible for their acidic properties. However, the reason is false because hydrogen ions do not contribute to an alkaline nature; rather, they make the solution acidic. In reality, hydroxide ions $(OH^-)$ contribute to an alkaline nature.

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Key Concept: Ion Formation

c) $Na^+$ and $OH^-$

[Solution Description] Sodium hydroxide $(NaOH)$ is a strong base and dissociates completely in water to produce sodium ions $(Na^+)$ and hydroxide ions $(OH^-)$. The dissociation can be represented by the equation:

$NaOH_{(s)} \rightarrow Na^+_{(aq)} + OH^-_{(aq)}$.

This means that in an aqueous solution, $NaOH$ produces $Na^+$ and $OH^-$ ions.

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Key Concept: Common Ion

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description] The assertion states a fundamental property of acids: they release hydrogen ions $(H^+)$ when dissolved in water, which gives them their characteristic acidic nature. This is true as per the syllabus. The reason correctly identifies that bases release hydroxide ions $(OH^-)$ in water, but it is not an explanation for why acids have acidic properties. Therefore, both statements are true, but the reason does not explain the assertion.

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Key Concept: Dilution Process

b) The concentration decreases.

[Solution Description] When hydrochloric acid ($HCl$) is diluted with water, the concentration of hydronium ions ($H_3O^+$) decreases. This is because dilution involves adding more solvent (water), which increases the volume of the solution while keeping the amount of solute (the acid) constant. The relationship is given by:

$\text{Concentration}_{\text{final}} = \frac{\text{Concentration}_{\text{initial}} \times \text{Volume}_{\text{initial}}}{\text{Volume}_{\text{final}}}$.

Thus, the concentration of $H_3O^+$ ions decreases.

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Key Concept: Strong vs Weak Acids

a) Hydrochloric acid

[Solution Description]

Hydrochloric acid is a strong acid that fully dissociates into hydrogen ions and chloride ions in water, making it a strong electrolyte.

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Key Concept: Dilution Effects

d) Assertion is false, but Reason is true.

[Solution Description]

When an acidic solution is diluted, water is added which leads to a decrease in the concentration of hydrogen ions $[H^+]$. Since pH is inversely related to the concentration of hydrogen ions $(pH = -\log_{10}[H^+])$, as the concentration of $[H^+]$ decreases, the pH value actually increases, not decreases. Therefore, Assertion is incorrect. The Reason is also incorrect because the concentration of hydrogen ions decreases with dilution, not increases.

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Key Concept: Relationship between pH values and hydrogen ion concentration

b) Decreases

[Solution Description]

The pH scale is logarithmic and inversely related to hydrogen ion concentration. Therefore, as the pH value increases, indicating a more basic solution, the concentration of $H^+$ ions decreases.

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Key Concept: pH and Chemical Reactions, pH and Industrial Applications

d) 7

[Solution Description] To find the pH after the reaction, we need to understand the products formed. The reaction between $\text{HCl}$ and $\text{Fe}$ can be represented as:

$\text{Fe} + 2\text{HCl} \rightarrow \text{FeCl}_2 + \text{H}_2$

After the reaction, there is no $\text{HCl}$ left, and $\text{FeCl}_2$ is formed. Since $\text{FeCl}_2$ does not affect the pH significantly compared to $\text{HCl}$, the initial acidic condition is neutralized. Therefore, the solution becomes closer to neutral, leading to a pH around 7.

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Key Concept: Baking Soda Reaction

c) Na_2CO_3, H_2O, and CO_2

[Solution Description]

Baking soda, which is chemically known as sodium bicarbonate $(\text{NaHCO}_3),$ decomposes upon heating to form sodium carbonate $(\text{Na}_2\text{CO}_3),$ water $(\text{H}_2\text{O}),$and carbon dioxide ($\text{CO}_2$). The decomposition reaction is given by:

$2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$

Thus, the products are sodium carbonate, water, and carbon dioxide.

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Key Concept: Real-world Application, Complex Reactions

c) Assertion is true, but Reason is false.

[Solution Description]

Sodium carbonate is indeed used in the glass industry because it acts as a flux, which helps lower the melting point of silica, allowing for easier and less costly processing. This statement is true. However, regarding the reason, sodium carbonate is a basic salt formed from a strong base (sodium hydroxide) and a weak acid (carbonic acid). When added to any mixture, including that for glass production, it would actually increase or maintain the alkalinity rather than reduce the pH, which means the solution becomes less acidic or remains basic. Hence, the assertion about its use is correct, but the explanation provided by the reason is incorrect since it inaccurately describes the effect on pH.

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Key Concept: Chlor-Alkali Process

a) $NaOH$, $Cl_2$, and $H_2$

[Solution Description]

In the chlor-alkali process, when aqueous sodium chloride $(\text{NaCl(aq)})$ undergoes electrolysis, it produces sodium hydroxide $(\text{NaOH})$, chlorine gas $(\text{Cl}_2)$, and hydrogen gas $(\text{H}_2).$ The balanced chemical equation for this process is:

$2\text{NaCl(aq)} + 2\text{H}_2\text{O(l)} \rightarrow 2\text{NaOH(aq)} + \text{Cl}_2\text{(g)} + \text{H}_2\text{(g)}$

Therefore, the products are sodium hydroxide, chlorine gas, and hydrogen gas.

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Key Concept: Salt pH Analysis, Industrial Processes

c) Neutral

[Solution Description] Potassium sulphate $K_2SO_4$ comes from a strong base KOH and a strong acid $H_2SO_4$, which makes it neutral. Calcium chloride $CaCl_2$ originates from a strong base $Ca(OH)_2$ and a strong acid HCl, also making it neutral. When both are mixed in equal moles, no significant hydrolysis occurs as both components produce neutral solutions. Thus, the overall solution is expected to be neutral.

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