Class 10 Chapter 2 Acids, Bases and Salt

Key Concept: pH and Composition

b) Strong acid and weak base
[Solution Description] Ammonium chloride is formed from the neutralization of a strong acid (hydrochloric acid, HCl) and a weak base ammonia, $(NH_3)$ This results in an acidic salt solution with pH < 7. Click To Download Notes

Key Concept: Acid-Base Reaction

a) Magnesium chloride and water
[Solution Description] The reaction between magnesium oxide (MgO) and hydrochloric acid (HCl) is given by:
$\text{MgO} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\text{O}$
Thus, the products are magnesium chloride and water.

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Key Concept: Reaction of Metal Carbonates

d) Carbon dioxide
[Solution Description] When magnesium carbonate reacts with hydrochloric acid, carbon dioxide $(CO_2)$ is released as per the equation:
$MgCO_3 + 2HCl \rightarrow MgCl_2 + CO_2 + H_2O$

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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: Salt and Environmental Impact, Salt Reaction Mechanisms

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that excessive use of ammonium nitrate causes water eutrophication, which is a phenomenon where water bodies become overly enriched with nutrients, leading to excessive growth of algae and depletion of oxygen. This process is primarily caused by the presence of nitrate ions, which encourage algal blooms.

The reason mentions that ammonium nitrate dissolves in water to release nitrate ions. This statement is true as ammonium nitrate $(NH_4NO_3)$ dissociates in water into $NH_4^+$ and $NO_3^-$ ions. The nitrate ions $(NO_3^-)$ indeed promote plant growth and are responsible for eutrophication when present in excess.

Hence, both the assertion and reason are true, and the reason correctly explains why excessive use of ammonium nitrate can lead to eutrophication.

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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 Formation

b) $H_2SO_4 \quad \text{and} \quad Ca(OH)_2$
[Solution Description] Calcium sulfate $\text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2$ with calcium hydroxide $\text{Ca(OH)}_2$

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Key Concept: Industrial Salt Process, Salt Family Classification

b) Solvay process; Carbonate family
[Solution Description]
Sodium carbonate is produced via the Solvay process, where the main reactants include sodium chloride and limestone. The production involves bubbling carbon dioxide through a concentrated solution of sodium chloride and ammonia. Sodium carbonate belongs to the carbonate family due to its anion $(CO_3^{2-})$.

Notes: Industrial Salt Process:

• Manufacture of Sodium Chloride: Sodium chloride is obtained mainly from sea water or rock salt.
• Process: The sea water is evaporated in large ponds to obtain salt. In the case of rock salt, it is mined and purified.
• Electrolysis: Sodium chloride is subjected to electrolysis in the industrial process to produce chlorine gas, hydrogen gas, and sodium hydroxide.

Salt Family Classification:

1. Normal Salts: Formed by the neutralization of an acid with a base (e.g., NaCl).
2. Acidic Salts: Formed from the neutralization of a strong acid with a weak base (e.g., NH4Cl).
3. Basic Salts: Formed from the neutralization of a weak acid with a strong base (e.g., Na2CO3).
4. Double Salts: Contain two different salts (e.g., Mohr’s salt).

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Key Concept: Real-world Application

b) It enhances the flavor of the food.
[Solution Description] Table salt, which is sodium chloride (NaCl), is commonly used in food preparation for various reasons including flavor enhancement, preservation, and as an essential nutrient source of sodium, which is vital for normal body function. Additionally, it helps in drawing out moisture and enhancing flavors.

Notes:

Real-world Applications

1. Cleaning Agents: Acids like hydrochloric acid (HCl) remove rust, while bases like sodium hydroxide are used in drain cleaners.
2. Food Industry: Acetic acid (vinegar) is used in food preservation; citric acid adds flavor.
3. Medicines: Antacids like magnesium hydroxide neutralize excess stomach acid.
4. Agriculture: Lime (calcium oxide) neutralizes acidic soil.
5. Manufacturing: Sulfuric acid is essential in fertilizers, and sodium hydroxide is used in soap production.
6. Testing: Litmus and pH indicators help determine substance nature (acidic/basic).
7. Construction: Calcium hydroxide is used in cement and plaster.

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Key Concept: Comparative pH

c) Assertion is true, but Reason is false.
[Solution Description]Sodium acetate has a pH greater than 7.

Sodium acetate is formed from the neutralization of acetic acid (a weak acid) and sodium hydroxide (a strong base)

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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 pH Analysis, Neutralization Reaction Analysis

c) Sodium sulfate is a neutral salt with a pH of exactly 7.
[Solution Description] Sulfuric acid $(\text{H}_2\text{SO}_4)$ is a strong acid, and sodium hydroxide (NaOH) is a strong base. When they react, they form sodium sulfate $(\text{Na}_2\text{SO}_4)$, a neutral salt because both the acid and base are strong. The balanced equation for the reaction is:
$\text{H}_2\text{SO}_4 + 2\text{NaOH} \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$
Since both components are strong, the resulting solution will have a pH of 7.

Notes:

Salt pH Analysis:

• Salts are formed by the neutralization of acids and bases.
• The pH of a salt depends on the strength of the acid and base used.
  • Neutral salts: Formed from strong acid and strong base (e.g., NaCl, pH = 7).
  • Acidic salts: Formed from strong acid and weak base (e.g., NH4Cl, pH < 7).
  • Basic salts: Formed from weak acid and strong base (e.g., Na2CO3, pH > 7).

Neutralization Reaction Analysis:

• Neutralization is the reaction between an acid and a base to form salt and water.
• General reaction:
  Acid + Base → Salt + Water
• Example:
  HCl + NaOH → NaCl + H2O
• Neutralization reactions are exothermic, releasing heat.

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Key Concept: Reaction Analysis, Chemical Properties

d) Reactant forming ammonium chloride
[Solution Description] Ammonia $(NH_3)$ acts as a reactant that reacts with carbon dioxide $(CO_2)$ and water $(H_2O)$ in the presence of sodium chloride (NaCl) to form ammonium chloride $(NH_4Cl)$ and sodium bicarbonate $(NaHCO_3)$.

Notes:

Key Concept: Intermediate Products

c) Ammonium chloride
[Solution Description]
During the production of baking soda $(NaHCO_3)$, the reaction between sodium chloride (NaCl), water $(H_2O)$, carbon dioxide $(CO_2)$, and ammonia $(NH_3)$ forms ammonium chloride $(NH_4Cl)$ and then sodium bicarbonate precipitates out. Hence, ammonium chloride is the intermediate product formed first.

Notes:

Intermediate Products:

• Neutralization Reaction: Acid + Base → Salt + Water. It forms water and salt as the main products.
• Indicator Use: In neutralization, indicators like litmus or phenolphthalein help identify the point of neutralization.
• pH of Products: The pH of the product depends on the strength of the acid and base. Strong acids and bases produce neutral solutions (pH = 7).
• Salt Formation: Different acids and bases form different salts (e.g., HCl + NaOH → NaCl + H₂O).
• Acid Strength: Strong acids like HCl dissociate completely, while weak acids like acetic acid dissociate partially.

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Key Concept: Baking Soda Composition

b) $\text{NaHCO}_3$
[Solution Description] The chemical formula of baking soda is $ \text{NaHCO}_3 $, which stands for sodium bicarbonate. It consists of sodium, hydrogen, carbon, and oxygen ions.

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Key Concept: Basic Properties

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The assertion states that sodium hydrogencarbonate is used as an antacid, which is true because it neutralizes excess stomach acid. The reason explains that sodium hydrogencarbonate releases carbon dioxide gas when reacting with acids, which is also true and is part of the mechanism by which it works as an antacid. Thus, both the assertion and the reason are true, and the reason correctly explains the assertion.

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Key Concept: Restoration

c) It turns blue again
[Solution Description]
Adding water to the heated (anhydrous) copper sulphate restores its original blue color. This occurs as it regains its water of crystallization and reforms into hydrated copper sulphate.

Notes:

Key Concept: Real-World Application

c) It hardens quickly after mixing with water.
[Solution Description] Plaster of Paris, due to its properties of hardening quickly upon addition of water, makes it an ideal material for casting and mold-making. It allows for easy shaping before setting solidly.

Notes:

• Electricity and Magnetism:
  • Used in transformers, electric motors, and power generation.
  • Magnets in refrigerators, MRI machines, and speakers.
• Chemical Reactions:
  • Essential in industries for producing fertilizers, medicines, and cleaning agents.
  • Combustion reactions power vehicles and generate heat.
• Sound Waves:
  • Used in music systems, hearing aids, and ultrasound imaging.
  • Sonar systems in submarines to detect underwater objects.
• Optics:
  • Applications in eyeglasses, cameras, microscopes, and telescopes.
  • Fiber optics for fast data transmission.
• Motion and Force:
  • Essential in designing vehicles, airplanes, and robotics.
  • Applied in sports for optimizing athlete performance.

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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: Application in Medicine

b) For supporting fractured bones
[Solution Description] In the medical field, Plaster of Paris is primarily used for supporting fractured bones by forming casts that immobilize bone segments, aiding in proper healing. Therefore, the correct answer is b).

Notes:

Key Concept: Comparative Analysis, Chemical Process Insight

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The assertion states that Plaster of Paris has less water of crystallization than gypsum, which is correct. Gypsum $(CaSO_4 \cdot 2H_2O)$ has two water molecules per formula unit, while Plaster of Paris $(CaSO_4 \cdot \frac{1}{2}H_2O)$ has half a water molecule shared between two formula units, effectively having one water per formula unit. This reduction occurs during heating gypsum at 373 K, confirming that both statements are true, and the reason explains why the assertion is true.

Starting with gypsum:

$\text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{373 \, \text{K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \text{H}_2\text{O}$

Thus, this chemical reaction supports the explanation provided in Reason for the Assertion’s truth.

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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: 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: Indicator Identification

c) Onion juice

[Solution Description] An olfactory indicator is a substance whose smell changes in acidic or basic solutions. Onion juice is commonly used as an olfactory indicator.

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Key Concept: Real-world Application, Reaction Equations

a) $\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$

[Solution Description]

The objective is to identify the balanced chemical reaction occurring when calcium hydroxide reacts with carbon dioxide in water to produce calcium carbonate and water. We begin by writing the unbalanced equation:

$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$

To balance, ensure equal numbers of each type of atom on both sides:

Start with calcium (Ca):

– 1 Ca on both sides.

Next, balance the oxygen atoms:

– On the left: 2 from $\text{Ca(OH)}_2$ + 2 from $\text{CO}_2$ = 4 oxygens.

– On the right: 3 in $\text{CaCO}_3$ + 1 in $\text{H}_2\text{O}$ = 4 oxygens.

Finally, check hydrogen:

– 2 H on both sides from $\text{H}_2\text{O}$.

Therefore, the balanced equation is:

$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$

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Key Concept: pH Scale Understanding

c) It is weakly acidic.

[Solution Description] The pH scale ranges from 0 to 14, where values below 7 indicate acidity, and values above 7 indicate alkalinity. A pH of 7 is neutral. Since the given pH value is 5, it indicates that the solution is acidic. The closer the pH value is to 0, the stronger the acid; thus, a pH of 5 represents a weak acid.

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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: Reaction Observation

c) Formation of zinc sulfate and hydrogen gas

[Solution Description]

Acids generally react with metals to release hydrogen gas along with a salt. For sulfuric acid $(\text{H}_2\text{SO}_4)$ reacting with zinc $(\text{Zn}),$ the reaction can be represented as:

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

Therefore, the reaction produces hydrogen gas.

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Key Concept: Conductivity in Solutions, Reaction with Metals

c) Solution A has a higher ionic concentration than Solution B.

[Solution Description]

To solve this problem, we need to understand that the brightness of the bulb is linked to the conductivity of the solution, which is dependent on the concentration of ions present. Acids dissociate in water to release $\text{H}^+$ ions, contributing to conductivity. If Solution A makes the bulb glow brighter than Solution B, it indicates that Solution A has a higher concentration of ions. Since acids react with metals, producing hydrogen gas and releasing more ions, Solution A is likely a stronger acid or at a higher concentration than Solution B.

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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: pH Identification

c) Assertion is true, but Reason is false.

[Solution Description] The pH scale ranges from 0 to 14, where a pH less than 7 indicates an acidic solution, a pH of 7 indicates a neutral solution, and a pH greater than 7 indicates a basic or alkaline solution. Therefore, the assertion is true because a pH of 9 signifies that the solution is indeed basic. However, the reason is false because a pH value greater than 7 actually indicates a basic or alkaline solution, not an acidic one.

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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: eaction Products

a) Calcium sulfate, carbon dioxide, and water

[Solution Description]

Calcium carbonate $(\text{CaCO}_3)$ reacts with sulfuric acid $(\text{H}_2\text{SO}_4)$ to form calcium sulfate $(\text{CaSO}_4),$ carbon dioxide $(\text{CO}_2),$ and water $(\text{H}_2\text{O}).$ The balanced chemical equation is:

$\text{CaCO}_3\text{(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{CaSO}_4\text{(s)} + \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)}$

This reaction produces a salt, gas, and water as expected.

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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: 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: Complex Reaction Mechanism, Advanced Conductivity

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

[Solution Description] When a strong acid is mixed with a strong base, they undergo a neutralization reaction:

$H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$

Initially, both the strong acid and base have high concentrations of ions, leading to high conductivity. As they neutralize each other, forming water, the concentration of ions in the solution decreases, resulting in reduced conductivity.

Water itself has very low ionic mobility compared to $H^+$ and $OH^-$ ions because it does not dissociate significantly into ions under normal conditions, thus reducing the overall conductivity. Eventually, when all ions are neutralized, the conductivity stabilizes at a lower level corresponding to the presence of any remaining minor ionic impurities.

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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: pH Scale Understanding, Hydrogen Ion Formation

c) 4.3

[Solution Description]

The initial concentration of hydrogen ions $[H^+]$ in the solution can be calculated from its pH using the formula:

$[H^+] = 10^{-4} \, M$

When the solution is diluted by adding an equal volume of water, the concentration of hydrogen ions becomes half because the volume doubles. Therefore, the new concentration is:

$[H^+]_{\text{new}} = \frac{10^{-4}}{2} = 5 \times 10^{-5} \, M$

To find the new pH:

$\text{New pH} = -\log(5 \times 10^{-5})$

By calculating:

$\text{New pH} = 4.3 \text{ (approximately)}$

So, the new pH of the solution is approximately 4.3.

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Key Concept: pH Scale

c) The solution is basic.

[Solution Description] The pH scale measures the acidity or alkalinity of a solution. A pH less than 7 indicates an acidic solution, a pH of 7 is neutral, and a pH greater than 7 indicates a basic or alkaline solution. Since the given solution has a pH of 10, it is basic or alkaline.

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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: Use of universal indicators

d) Violet

[Solution Description]

Universal indicators provide a color change across a wide pH spectrum. When added to a strong base, which has a high pH typically greater than 11, a universal indicator will show a violet or purple color.

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Key Concept: pH and Chemical Reactions, pH Sensitivity in Organisms

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

[Solution Description]

The assertion states that a change in pH from 6 to 5 impacts aquatic life, which is true because many aquatic organisms are sensitive to changes in pH, as their biological processes depend on stable conditions. Even small shifts can cause stress or harm.

The reason accurately refers to the nature of the pH scale: it is logarithmic, where each integer drop in pH corresponds to a tenfold increase in $H^+$ ion concentration. Therefore, a change from pH 6 to pH 5 indicates a significant increase in acidity.

Both statements individually are correct, and the reason that describes the logarithmic pH scale correctly explains why a shift from pH 6 to 5 has such a substantial impact on aquatic life.

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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: Complex Salt Families, Chlor-Alkali Process

a) Successful production of KOH but no $Cl_2$

[Solution Description] In the chlor-alkali process, the electrolysis of NaCl produces NaOH, $Cl_2$, and $H_2$. The replacement of NaCl with $K_2SO_4$ would not work directly since $K_2SO_4$ dissociates into $K^+$ and $SO_4^{2-}$, and sulfate ions do not undergo the same electrochemical reactions. $Cl_2(g)$ production depends on chloride ions, which aren’t present in $K_2SO_4$.

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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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Key Concept: Chlor-alkali Process

c) Sodium hydroxide, chlorine, hydrogen

[Solution Description] The chlor-alkali process involves the electrolysis of sodium chloride $(NaCl)$ in water, which produces three primary products: sodium hydroxide $(NaOH),$ chlorine $(Cl_2),$ and hydrogen $(H_2).$ These substances have a wide range of industrial and commercial uses.

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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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