📘 Model Test Questions Class 10 Chemistry Test # 3 for Chapter # 2 (Acids, Bases and Salts)
(Three Concepts of acids, bases, pH, pOH, Kw, Salts, its types, preparation and uses, Buffers)
Prepared by Inam Jazbi – Learn Chemistry
📘 Short Answer-Questions (SLO based)
Prepared by Inam Jazbi – Learn Chemistry
Q1.
What is Bronsted-Lowery acid-base theory? Define Bronsted-Lowry base and explain with an example that water is a Bronsted-Lowry base.
Q2.
What are conjugate acid-base pairs? Explain with examples.
Differentiate between proton transfer and electron pair transfer in acid-base reactions.
Q3.
Classify the following solutions as acidic, basic or neutral
(i) A solution that has [H⁺] = 1 x 10⁻⁴ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
(ii) A solution that has [H⁺] = 1 x 10⁻¹¹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iii) A solution that has [H⁺] = 1 x 10⁻⁹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iv) A solution that has [H⁺] = 1 x 10⁻³ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
Q4.
Elaborate the ionization equation of water. Explain in detail that how water ionization is related with pH of solution? Explain the relationship between Kw, pH, and pOH.
Q5.
Define the following terms:
(a) pH (b) Indicator (c) Neutralization (d) Titration (e) Normal salt (f) Basic salt
Q6.
Define buffers. What is the composition of buffers? Discuss its importance in our daily life.
Q7.
Classify a solution with pH = 3, 7, and 10. Name three common household substances having
a. pH value greater than 7 (Bitter-gourd, coffee and chocolate)
b. pH value less than 7 (curd, vinegar, lemon and orange)
c. pH value equal to 7 (sugar, common salt, pure water)
Q8.
Name the acids present in:
i. Vinegar (acetic acid)
ii. Ant sting (formic acid)
iii. Citrus fruit (citric acid)
iv. Sour milk (lactic acid)
Q9.
What are conjugate bases of each of the following?
HS⁻, H₃O⁺, H₂PO₄⁻, HSO₄⁻, HF, CH₃COOH, [Al(H₂O)₆]³⁺
Q10.
Give the conjugate acids of the following:
OH⁻, HCO₃⁻, HPO₄²⁻, CH₃NH₂, CO₃²⁻, CH₃COO⁻
Q11.
Which of the following behave both as Bronsted acids and Bronsted bases?
H₂O, HCO₃⁻, H₂SO₄, H₃PO₄, HS⁻
Q12.
What do you mean by neutralization reaction according to Arrhenius acid-base concept? What do you mean by balancing of neutralization reaction with the help of examples?
Q13.
You are having a strong acid (HNO₃) and strong base (NaOH) on mixing
i. What type of salt you will have?
ii. What type of reaction will it be?
iii. Will it be soluble or insoluble salt?
iv. If it is soluble, how will it be recovered?
Q14.
Give brief answers of following:
(i). Why pure water is not a strong electrolyte?
(ii). Why ionic-product constant of water is temperature dependent?
(iii). Define a base and explain that all alkalis are bases, but all bases are not alkalis.
(iv). Which kind of bond is formed between Lewis acid and a base? Name the product formed between them
(v). Why H⁺ ion acts as a Lewis acid?
(vi). Name two acids used in the manufacture of fertilizers.
(vii).Write the chemical formulae and the names of three Arrhenius acid and bases
(viii).What do you mean by neutralization reaction according to Arrhenius acid-base concept?
(ix).Prove that water is an amphoteric specie.
(x). Identify the acid and base in the reaction:
HCl + H₂O → H₃O⁺ + Cl⁻ (using Brønsted–Lowry concept).
(xi). Classify NH₃ as an acid or base under all three concepts.
(xii). Give one example where a substance acts as a Lewis acid and a Lewis base.
(xiii). Show that pure water is neutral using Kw.
(xiv). How does temperature affect the value of Kw?
(xv). Explain why carbon dioxide gas is released in some salt preparations.
(xvi). Write chemical equations for salt preparation by:
✨Acid + Base
✨ Acid + Metal
✨ Acid + Carbonate
(xvii). Why is the pH of blood important to maintain? Or Why is maintaining pH important in biological systems?
(xviii). A substance does not produce H⁺ ions in water but still behaves as an acid. Explain this using the Lewis concept.
(xix). Analyze a reaction where a substance behaves as both acid and base (amphoteric behavior).
📘 Long Questions (SLO based)
Prepared by Inam Jazbi – Learn Chemistry
Q1.
Describe salts, preparation of salts and types of salts.
Q2.
State and explain Lewis concept of acids and bases with two examples. Explain why the Lewis concept is more general than the other two.
Q3.
Discuss in detail how different solutions in aqueous system exhibit increase in acidity and increase in basicity on the basis of H⁺ and OH⁻?
Q4.
Write down the uses of salt in daily life.
Q5.
Elaborate the Arrhenius concept of acid and base with suitable examples. Why is the Arrhenius concept limited compared to Brønsted–Lowry theory? Which of the following is/are Arrhenius acids and bases?
(a) Ca(OH)₂ (b) HNO₃ (c) NaOH (d) H₂SO₄ (e) KOH
Q6.
A solution of HCl has pH of 2.3. Calculate its pOH and [H⁺]?
Q7.
Find pH, pOH, [OH⁻] and [H⁺] of 2.46 x 10⁻⁹ M KOH solution.
📘 Smart Answers Short Questions of Model Test Questions Class 10 Chemistry Test # 3 for Chapter # 2 (Acids, bases and salts)
Prepared by Inam Jazbi – Learn Chemistry
Q1. What is Bronsted-Lowery acid-base theory? Define Bronsted-Lowry base and explain with an example that water is a Bronsted-Lowry base.
Answer
📌 Brønsted–Lowry Theory:
It states that an acid is a proton (H⁺) donor and a base is a proton (H⁺) acceptor.
📌 Definition of Brønsted-Lowry Base:
A substance that accepts a proton (H⁺) is called a Brønsted-Lowry base.
📌 Example (Water acting as base):
HCl + H₂O ⇌ H₃O⁺ + Cl⁻
🧪 Explanation:
In this reaction, water (H₂O) accepts a proton (H⁺) from hydrochloric acid (HCl) and forms hydronium ion (H₃O⁺). Therefore, water acts as a Brønsted–Lowry base.(H₃O⁺ is called conjugate acid and Cl⁻ is a conjugate base).
It states that an acid is a proton (H⁺) donor and a base is a proton (H⁺) acceptor.
📌 Definition of Brønsted-Lowry Base:
A substance that accepts a proton (H⁺) is called a Brønsted-Lowry base.
📌 Example (Water acting as base):
HCl + H₂O ⇌ H₃O⁺ + Cl⁻
🧪 Explanation:
In this reaction, water (H₂O) accepts a proton (H⁺) from hydrochloric acid (HCl) and forms hydronium ion (H₃O⁺). Therefore, water acts as a Brønsted–Lowry base.(H₃O⁺ is called conjugate acid and Cl⁻ is a conjugate base).
Q2. What are conjugate acid-base pairs? Explain with examples. Differentiate between proton transfer and electron pair transfer in acid-base reactions.
Answer
🔗 Conjugate Acid–Base Pair
A conjugate acid–base pair consists of two species that differ by the presence or absence of a proton (H⁺). When an acid loses a proton, its conjugate base is formed, and when a base gains a proton, its conjugate acid is formed.
📌 General Idea:
Acid → loses H⁺ → Conjugate Base
Acid ⇌ Conjugate Base + H⁺
Base → gains H⁺ → Conjugate Acid Base + H⁺ ⇌ Conjugate Acid
📌 Example:
CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺
⚗️ Proton Transfer (Brønsted–Lowry)
Acid donates H⁺ and base accepts H⁺.
Example: HCl + H₂O → H₃O⁺ + Cl⁻
⚡ Electron Pair Transfer (Lewis)
Base donates an electron pair and acid accepts it to form a coordinate bond.
Example: NH₃ + BF₃ → NH₃→BF₃
🧪 Key Difference:
• Brønsted–Lowry theory → transfer of H⁺ • Lewis theory → transfer of electron pair
Q3. Classify the following solutions as acidic, basic or neutral.
(i) A solution that has [H⁺] = 1 x 10⁻⁴ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
(ii) A solution that has [H⁺] = 1 x 10⁻¹¹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iii) A solution that has [H⁺] = 1 x 10⁻⁹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iv) A solution that has [H⁺] = 1 x 10⁻³ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
(i) A solution that has [H⁺] = 1 x 10⁻⁴ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
(ii) A solution that has [H⁺] = 1 x 10⁻¹¹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iii) A solution that has [H⁺] = 1 x 10⁻⁹ mol.dm⁻³ (basic as [H⁺] < 1 x 10⁻⁷ mol.dm⁻³)
(iv) A solution that has [H⁺] = 1 x 10⁻³ mol.dm⁻³ (acidic as [H⁺] > 1 x 10⁻⁷ mol.dm⁻³)
Answer
🧪 Classification of Solutions
A solution is:
• Acidic if [H⁺] > 1 × 10⁻⁷ mol.dm⁻³
• Neutral if [H⁺] = 1 × 10⁻⁷ mol.dm⁻³
• Basic if [H⁺] < 1 × 10⁻⁷ mol.dm⁻³
📌 Classification
(i) [H⁺] = 1 × 10⁻⁴ mol.dm⁻³
Acidic, because [H⁺] > 1 × 10⁻⁷ mol.dm⁻³.
(ii) [H⁺] = 1 × 10⁻¹¹ mol.dm⁻³
Basic, because [H⁺] < 1 × 10⁻⁷ mol.dm⁻³.
(iii) [H⁺] = 1 × 10⁻⁹ mol.dm⁻³
Basic, because [H⁺] < 1 × 10⁻⁷ mol.dm⁻³.
(iv) [H⁺] = 1 × 10⁻³ mol.dm⁻³
Acidic, because [H⁺] > 1 × 10⁻⁷ mol.dm⁻³.
Q4. Elaborate the ionization equation of water. Explain how water ionization is related to the pH of a solution. Explain the relationship between Kw, pH, and pOH.
Answer
💧 Ionization of Water
Water is a weak electrolyte and ionizes slightly into hydrogen ions (H⁺) and hydroxide ions (OH⁻). This process is called self-ionization or auto-ionization of water.
⚖️ Ionic Product of Water (Kw)
The auto-ionization of water is an equilibrium process and is characterized by an equilibrium constant (Kc).
📌 Ionization Equation:
H₂O ⇌ H⁺ + OH⁻
Since only a very small fraction of water molecules ionize, the concentration of unionized water remains nearly constant.
📌 Equilibrium Expression:
Kc = [H⁺][OH⁻] / [H₂O]
As [H₂O] is constant,
Kc × [H₂O] = [H⁺][OH⁻]
Kw = [H⁺][OH⁻]
At 25°C:
Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶
Kw is called the Ionic Product of Water or Dissociation Constant of Water. It determines the relationship between the concentrations of H⁺ and OH⁻ ions in aqueous solutions.
📌 In Pure Water at 25°C:
[H⁺] = [OH⁻]
Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴
[H⁺] = [OH⁻] = 1 × 10⁻⁷ mol.dm⁻³
Therefore, pure water is neutral because it contains equal concentrations of H⁺ and OH⁻ ions.
📊 Relation of Water Ionization with pH
The pH of a solution depends on the concentration of H⁺ ions produced by water ionization.
📌 Formula:
pH = −log[H⁺]
For pure water:
pH = −log(1 × 10⁻⁷) = 7
• If [H⁺] increases, pH decreases and the solution becomes acidic.
• If [H⁺] decreases, pH increases and the solution becomes basic.
🔗 Relationship Between Kw, pH and pOH
📌 Formula:
pOH = −log[OH⁻]
pH + pOH = 14
Since:
Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴
Therefore:
• Acidic solution: pH < 7 and pOH > 7
• Neutral solution: pH = 7 and pOH = 7
• Basic solution: pH > 7 and pOH < 7
Q5. Define the following terms:
(a) pH (b) Indicator (c) Neutralization (d) Titration (e) Normal Salt (f) Basic Salt
Answer
📊 (a) pH
pH is a measure of the hydrogen ion concentration (H⁺) in a solution. It is defined as the negative logarithm of hydrogen ion concentration.
📌 Formula:
pH = −log[H⁺]
The pH scale ranges from 0 to 14.
• pH < 7 → Acidic
• pH = 7 → Neutral
• pH > 7 → Basic
🎨 (b) Indicator
Indicators are weak organic acids or bases that change colour over a specific pH range.
📌 Example:
Litmus is red in acidic solutions and blue in basic solutions.
⚖️ (c) Neutralization
Neutralization is a reaction in which an acid reacts with a base to form salt and water.
📌 Example:
HCl + NaOH → NaCl + H₂O
🧪 (d) Titration
Titration is a laboratory technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
🧂 (e) Normal Salt (Neutral Salt)
A normal salt is formed by the complete neutralization of an acid with a base and contains no replaceable H⁺ or OH⁻ ions.
📌 Properties:
• Neutral to litmus
• pH = 7
📌 Example:
NaCl (Sodium Chloride)
🧫 (f) Basic Salt
A basic salt is formed by the partial neutralization of a base by an acid and contains replaceable hydroxide (OH⁻) ions.
📌 Properties:
• Produces a basic solution in water
• pH > 7
• Turns red litmus blue
📌 Example:
Mg(OH)Cl
Q6. Define buffers. What is the composition of buffers? Discuss their importance in daily life.
Answer
🧪 Buffer Solution
A buffer is a solution that resists changes in pH when small amounts of acid or base are added. It maintains a nearly constant pH.
⚗️ Composition of Buffers
Buffers are of two types:
📌 Acidic Buffer
Made of a weak acid and its salt (conjugate base).
Example: CH₃COOH + CH₃COONa
📌 Basic Buffer
Made of a weak base and its salt (conjugate acid).
Example: NH₃ + NH₄Cl
📊 Importance of Buffers in Daily Life
• Maintain pH of blood (carbonic acid–bicarbonate system) 🩸
• Help in biological and microbiological processes 🧫
• Used in industries like leather, paper, sugar, and pharmaceuticals 🏭
• Provide suitable pH for growth of microorganisms in culture media 🔬
• Improve crop growth by maintaining soil pH 🌱
• Used in food preservation and quality control 🍎
Q7. Classify a solution with pH = 3, 7, and 10. Name three common household substances having
(a) pH value greater than 7
(b) pH value less than 7
(c) pH value equal to 7
Answer
📊 Classification of pH Values
• pH = 3 → Acidic solution (strongly acidic) 🧪
• pH = 7 → Neutral solution 💧
• pH = 10 → Basic (alkaline) solution 🧼
🍽️ Household Substances (pH > 7)
• Bitter gourd 🥒
• Coffee ☕
• Chocolate 🍫
🍋 Household Substances (pH < 7)
• Curd 🥛
• Vinegar 🧴
• Lemon 🍋
• Orange 🍊
🍬 Household Substances (pH = 7)
• Sugar solution 🍯
• Common salt solution 🧂
• Pure water 💧
Q8. Name the acids present in:
i. Vinegar
ii. Ant sting
iii. Citrus fruit
iv. Sour milk
Answer
🧪 Acids in Common Substances
i. Vinegar → Acetic acid 🍶
ii. Ant sting → Formic acid 🐜
iii. Citrus fruit → Citric acid 🍊🍋
iv. Sour milk → Lactic acid 🥛
Q9. What are conjugate bases of each of the following? HS⁻, H₃O⁺, H₂PO₄⁻, HSO₄⁻, HF, CH₃COOH, [Al(H₂O)₆]³⁺
Answer
🧪 Conjugate Bases (by loss of H⁺)
A conjugate base is formed when a species loses one proton (H⁺).
📌 i. HS⁻ → S²⁻
(loss of H⁺)
📌 ii. H₃O⁺ → H₂O
(loss of H⁺)
📌 iii. H₂PO₄⁻ → HPO₄²⁻
(loss of H⁺)
📌 iv. HSO₄⁻ → SO₄²⁻
(loss of H⁺)
📌 v. HF → F⁻
(loss of H⁺)
📌 vi. CH₃COOH → CH₃COO⁻
(loss of H⁺)
📌 vii. [Al(H₂O)₆]³⁺ → [Al(H₂O)₅OH]²⁺
(loss of H⁺ from coordinated water molecule)
Q11. Which of the following behave both as Brønsted acids and Brønsted bases? H₂O, HCO₃⁻, H₂SO₄, H₃PO₄, HS⁻
Answer
⚖️ Amphiprotic Species (Act as Acid & Base)
A substance that can donate a proton (H⁺) as well as accept a proton is called amphiprotic. Such species behave both as Brønsted acids and Brønsted bases.
📌 From the given list, the amphiprotic species are:
• H₂O 💧 → can gain or lose H⁺
• HCO₃⁻ 🧪 → can act as acid or base
• HS⁻ 🧫 → can donate or accept H⁺
❌ Not amphiprotic:
• H₂SO₄ → only acid
• H₃PO₄ → mainly acid
📌 Final Answer:
H₂O, HCO₃⁻, HS⁻ behave both as Brønsted acids and Brønsted bases.
Q12. What do you mean by neutralization reaction according to Arrhenius acid-base concept? What do you mean by balancing of neutralization reaction with the help of examples?
Answer
⚗️ Neutralization Reaction
According to Arrhenius concept, a chemical reaction between an acid and a base in aqueous solution that produces salt and water is called a neutralization reaction.
Example:
HCl + NaOH → NaCl + H₂O
⚖️ Balancing of Neutralization Reaction
A neutralization reaction is balanced when the number of atoms and the total positive and negative charges are equal on both sides of the equation. It involves the equal consumption of H⁺ and OH⁻ ions.
While balancing, the acidity of the acid and the basicity of the base must be considered.
📌 Example 1:
One mole of HCl provides one mole of H⁺ and one mole of NaOH provides one mole of OH⁻, so the ratio is 1:1.
NaOH + HCl → NaCl + H₂O
📌 Example 2:
NaOH or KOH also reacts with HBr, HI, and HNO₃ in a 1:1 ratio because each acid releases one H⁺ ion.
KOH + HNO₃ → KNO₃ + H₂O
📌 Final Answer:
Neutralization is the reaction of an acid and a base to form salt and water. Balancing ensures equal numbers of atoms and equal amounts of H⁺ and OH⁻ ions in the reaction.
Q13. You are having a strong acid (HNO₃) and strong base (NaOH) on mixing:
i. What type of salt will you have?
ii. What type of reaction will it be?
iii. Will it be a soluble or insoluble salt?
iv. If it is soluble, how will it be recovered?
Answer
🧪 (i) Type of Salt Formed
When a strong acid (HNO₃) reacts with a strong base (NaOH), complete neutralization occurs and a normal salt is formed.
📌 Example:
HNO₃ + NaOH → NaNO₃ + H₂O
⚗️ (ii) Type of Reaction
This is a neutralization reaction in which an acid reacts with a base to form salt and water.
💧 (iii) Solubility of Salt
The salt formed, sodium nitrate (NaNO₃), is soluble in water because all nitrate salts are water soluble.
🧂 (iv) Recovery of Salt
If the salt is soluble in water, it can be recovered by crystallization after evaporating excess water.
Q14. Give brief answers of following:
(i) Why pure water is not a strong electrolyte?
(ii) Why ionic-product constant of water is temperature dependent?
(iii) Define a base and explain that all alkalis are bases, but all bases are not alkalis.
(iv) Which kind of bond is formed between Lewis acid and a base? Name the product formed between them
(v) Why H⁺ ion acts as a Lewis acid?
(vi) Name two acids used in the manufacture of fertilizers.
(vii) Write chemical formulae and names of three Arrhenius acids and bases
(viii) What is neutralization reaction according to Arrhenius concept?
(ix) Prove that water is amphoteric.
(x) Identify acid and base in: HCl + H₂O → H₃O⁺ + Cl⁻
(xi) Classify NH₃ under all three acid-base concepts.
(xii) Give one example where a substance acts as both Lewis acid and base.
(xiii) Show that pure water is neutral using Kw.
(xiv) How does temperature affect Kw?
(xv) Why is CO₂ released in some salt preparations?
(xvi) Write equations for salt preparation by acid + base, acid + metal, acid + carbonate
(xvii) Why is pH of blood important?
(xviii) Explain acid behavior without H⁺ using Lewis concept.
(xix) Give one example of amphoteric behavior.
(i) Why pure water is not a strong electrolyte?
(ii) Why ionic-product constant of water is temperature dependent?
(iii) Define a base and explain that all alkalis are bases, but all bases are not alkalis.
(iv) Which kind of bond is formed between Lewis acid and a base? Name the product formed between them
(v) Why H⁺ ion acts as a Lewis acid?
(vi) Name two acids used in the manufacture of fertilizers.
(vii) Write chemical formulae and names of three Arrhenius acids and bases
(viii) What is neutralization reaction according to Arrhenius concept?
(ix) Prove that water is amphoteric.
(x) Identify acid and base in: HCl + H₂O → H₃O⁺ + Cl⁻
(xi) Classify NH₃ under all three acid-base concepts.
(xii) Give one example where a substance acts as both Lewis acid and base.
(xiii) Show that pure water is neutral using Kw.
(xiv) How does temperature affect Kw?
(xv) Why is CO₂ released in some salt preparations?
(xvi) Write equations for salt preparation by acid + base, acid + metal, acid + carbonate
(xvii) Why is pH of blood important?
(xviii) Explain acid behavior without H⁺ using Lewis concept.
(xix) Give one example of amphoteric behavior.
Answer
🧪 (i) Pure water not strong electrolyte
Water ionizes very slightly into H⁺ and OH⁻ (because of its strong hydrogen bonding), so it produces very few ions → weak electrolyte.
🌡️ (ii) Temperature effect on Kw
Higher temperature increases ionization of water, so Kw increases.
⚗️ (iii) Base & alkali
A base produces OH⁻ ions in solution. Alkalis are water-soluble bases. All alkalis are bases, but not all bases dissolve in water.
🔗 (iv) Lewis bond & product
A coordinate covalent bond is formed. Product is called a Lewis adduct.
Example: NH₃ + BF₃ → NH₃→BF₃
⚡ (v) Why H⁺ is Lewis acid
H⁺ has no electrons and accepts an electron pair → acts as Lewis acid.
🧪 (vi) Fertilizer acids
Nitric acid (HNO₃) and Sulphuric acid (H₂SO₄)
📘 (vii) Arrhenius acids & bases
Acids: Hydrochloric acid; HCl, Nitric acid; HNO₃, Sulphuric acid; H₂SO₄
Bases: Sodium hydroxide; NaOH, Potassium hydroxide; KOH, Calcium hydroxide; Ca(OH)₂
💧 (viii) Neutralization (Arrhenius)
According to Arrhenius theory neutralization is a reaction between an acid and a base in their aqueous solutions producing salt and unionized water. Acid + base → salt + water
According to Arrhenius theory, strong acids, strong bases, and salts dissociate completely into ions in aqueous solution. The ions that remain unchanged during the reaction are called spectator ions and can be omitted. The net ionic equation for neutralization is:
H⁺ + OH⁻ → H₂O
Thus, neutralization is the reaction in which H⁺ ions from an acid combine with OH⁻ ions from a base to form unionized water molecules.
💧 (ix) Water is amphoteric
A substance that can behave as both an acid and a base is referred to as an amphoteric substance.Water acts as acid and base:
H₂O + HCl → H₃O⁺ + Cl⁻ (water acts as a base)
H₂O + NH₃ → NH₄⁺ + OH⁻ (water acts as an acid)
⚗️ (x) Brønsted pair
Acid: HCl
Base: H₂O
🧫 (xi) NH₃ classification
Brønsted base, Lewis base, Arrhenius baseArrhenius: NH₃ is a base because it produces OH⁻ ions in water.
Brønsted–Lowry: NH₃ is a base because it accepts a proton (H⁺).
Lewis: NH₃ is a base because it donates a lone pair of electrons.
🔬 (xii) Lewis acid & base example
BF₃ (acid) + NH₃ (base) → NH₃→BF₃
💧 (xiii) Neutral water
Kw = [H⁺][OH⁻] = 1×10⁻¹⁴
⇒ [H⁺] = [OH⁻] = 1×10⁻⁷ → pH = 7 (neutral)
🌡️ (xiv) Effect of temperature
Increasing temperature increases Kw.
🧪 (xv) CO₂ release
Carbonates react with acids where they are decomposed into CO₂ gas along with salt and water.
⚗️ (xvi) Salt preparation
Acid + Base: HCl + NaOH → NaCl + H₂O
Acid + Metal: 2HCl + Zn → ZnCl₂ + H₂
Acid + Carbonate: 2HCl + CaCO₃ → CaCl₂ + CO₂ + H₂O
🩸 (xvii) Blood pH importance
Blood pH must stay ~7.4 for enzyme and body function.
⚡ (xviii) Lewis acid idea
Acids accept electron pairs, not necessarily H⁺ (e.g., BF₃).A substance that does not produce H⁺ ions in water can still be an acid if it accepts an electron pair; such substances are called Lewis acids.
🔄 (xix) Amphoteric example
H₂O acts as acid and base depending on reaction.Example: Auto-ionization of water
2H₂O ⇌ H₃O⁺ + OH⁻
Analysis:
One H₂O molecule donates a proton (H⁺) and acts as an acid.
The other H₂O molecule accepts a proton (H⁺) and acts as a base.
Conclusion:
Since water can act as both an acid and a base in the same reaction, it exhibits amphoteric (amphiprotic) behavior.
📘 Smart Answers of Long Questions of Model Test Questions Class 10 Chemistry Test # 3 for Chapter # 2 (Acids, Bases and Salts)
Prepared by Inam Jazbi – Learn Chemistry
Q1. Describe salts, preparation of salts and types of salts.
Answer
🧂 Definition of Salt
A salt is an ionic crystalline compound formed during the neutralization of an acid and a base. It consists of a cation (from the base) other than H⁺ and an anion (from the acid) other than OH⁻.
📌 Examples:
NaCl, CuCl₂, K₂SO₄
HCl + NaOH → NaCl + H₂O
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
📚 Three Main Types of Salts
1. Normal Salts
Formed by complete neutralization of an acid and a base. pH = 7.
2. Acid Salts
Formed by partial neutralization of an acid. pH < 7.
3. Basic Salts
Formed by partial neutralization of a base. pH > 7.
🧪 Examples of Salts
Normal Salts:
NaCl, KCl, Na₂SO₄, K₂SO₄, Na₃PO₄
Acid Salts:
NaHCO₃, NaHSO₄, NH₄Cl, Ca(NO₃)₂
Basic Salts:
KCN, K₂CO₃, Na₂CO₃, CH₃COONa, Mg(OH)Cl
⚖️ Normal (Neutral) Salts
Salts obtained by complete neutralization of a strong acid and a strong base. They contain no replaceable H⁺ or OH⁻ ions and are neutral to litmus.
📌 Examples:
NaCl, NaBr, NaNO₃, KCl, Na₂SO₄
🧫 Acid Salts
Salts formed by partial neutralization of an acid and contain replaceable hydrogen ions. Their solutions have pH less than 7.
📌 Examples:
NaHCO₃, NaHSO₄, NH₄Cl, Ca(NO₃)₂
🔵 Basic Salts
Salts formed by partial neutralization of a base and contain replaceable hydroxyl ions. Their solutions have pH greater than 7.
📌 Examples:
KCN, K₂CO₃, Na₂CO₃, CH₃COONa, Mg(OH)Cl
⚗️ Preparation of Salts
Salts are prepared by the action of acids on metals, bases, metal oxides, carbonates and bicarbonates.
1. Acid + Metal → Salt + Hydrogen
2HCl + Mg → MgCl₂ + H₂
2. Acid + Base → Salt + Water
HNO₃ + KOH → KNO₃ + H₂O
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
3. Acid + Metal Oxide → Salt + Water
H₂SO₄ + CaO → CaSO₄ + H₂O
4. Acid + Carbonate → Salt + Water + CO₂
2HNO₃ + BaCO₃ → Ba(NO₃)₂ + H₂O + CO₂
📌 Final Answer:
Salts are ionic compounds formed by the neutralization of acids and bases. They are classified into normal, acid and basic salts and can be prepared by the reaction of acids with metals, bases, metal oxides and carbonates.
Q2. State and explain Lewis concept of acids and bases with two examples. Explain why the Lewis concept is more general than the other two.
Answer
🧪 Lewis Concept of Acids and Bases
Gilbert N. Lewis proposed his concept of acids and bases in 1923.
According to Lewis:
• A Lewis acid is a substance that can accept an electron pair.
• A Lewis base is a substance that can donate an electron pair.
Hence, a Lewis acid is an electron pair acceptor and a Lewis base is an electron pair donor.
⚗️ Example # 1
Consider the reaction between H⁺ and H₂O.
The proton (H⁺) accepts an electron pair, while H₂O donates an electron pair to form a coordinate covalent bond.
H⁺ + H₂O → H₃O⁺
📌 H⁺ is a Lewis acid and H₂O is a Lewis base.
⚗️ Example # 2
Consider the reaction between NH₃ and BF₃.
NH₃ donates a lone pair of electrons and acts as a Lewis base, while BF₃ accepts the electron pair and acts as a Lewis acid.
NH₃ + BF₃ → H₃N→BF₃
The product formed is called an adduct and contains a coordinate covalent bond.
🌍 Why Lewis Concept is More General
The Lewis concept is more general than the Arrhenius and Brønsted-Lowry concepts because it does not require the presence of H⁺ ions.
It explains acid-base reactions involving the transfer of electron pairs, including reactions where no proton is involved.
Therefore, all Arrhenius acids and bases and all Brønsted-Lowry acids and bases can be explained by the Lewis concept, but not all Lewis acids and bases can be explained by the other two concepts.
📌 Final Answer:
A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. The Lewis concept is the most general acid-base concept because it explains reactions involving electron pair transfer even in the absence of H⁺ ions.
Q3. Discuss in detail how different solutions in aqueous system exhibit increase in acidity and increase in basicity on the basis of H⁺ and OH⁻.
Answer
💧 Acidity and Basicity in Aqueous Solutions
In aqueous solutions, the acidic or basic nature of a solution depends upon the concentration of H⁺ and OH⁻ ions.
Acidic Solution:
When the concentration of H⁺ ions is greater than that of OH⁻ ions, the solution is acidic.
[H⁺] > [OH⁻]
Basic Solution:
When the concentration of OH⁻ ions is greater than that of H⁺ ions, the solution is basic.
[OH⁻] > [H⁺]
Neutral Solution:
When the concentrations of H⁺ and OH⁻ ions are equal, the solution is neutral.
[H⁺] = [OH⁻]
📈 Increase in Acidity
Acidity increases when the concentration of H⁺ ions increases and the concentration of OH⁻ ions decreases.
Example:
HCl(aq) → H⁺(aq) + Cl⁻(aq)
Addition of HCl increases the number of H⁺ ions, making the solution more acidic.
📉 Increase in Basicity
Basicity increases when the concentration of OH⁻ ions increases and the concentration of H⁺ ions decreases.
Example:
NaOH(aq) → Na⁺(aq) + OH⁻(aq)
Addition of NaOH increases the number of OH⁻ ions, making the solution more basic.
⚖️ Summary
• Increase in H⁺ concentration → Increase in acidity
• Increase in OH⁻ concentration → Increase in basicity
• Equal concentrations of H⁺ and OH⁻ → Neutral solution
📌 Final Answer:
The acidic or basic nature of an aqueous solution depends on the relative concentrations of H⁺ and OH⁻ ions. Higher H⁺ concentration increases acidity, whereas higher OH⁻ concentration increases basicity.
Q4. Write down the uses of salts in daily life.
Answer
🧂 Uses of Salts in Daily Life
Salts have numerous applications in agriculture, medicine and industry. Some important uses are given below:
🌾 1. Fertilizers
Many chemical fertilizers used in agriculture are salts.
📌 Examples:
Ammonium chloride (NH₄Cl), Ammonium nitrate (NH₄NO₃), Ammonium phosphate and Potassium chloride (KCl).
🐛 2. Pesticides
Certain salts are used as pesticides to destroy insects, pests, weeds and fungi.
📌 Examples:
Copper(II) sulphate (CuSO₄), Iron(II) sulphate (FeSO₄) and Mercury chloride (HgCl₂).
🏥 3. Plaster Casts
Hydrated calcium sulphate (CaSO₄·2H₂O) is used in Plaster of Paris for supporting broken bones.
💊 4. Iron Supplements
Iron(II) sulphate heptahydrate (FeSO₄·7H₂O) is used in iron tablets for patients suffering from anemia.
🍽️ 5. Antacid
Sodium hydrogen carbonate (NaHCO₃) is used as an antacid to neutralize excess stomach acid.
🩻 6. X-Ray Examination
Barium sulphate (BaSO₄) is used in barium meals to make internal organs visible in X-ray films.
🦠 7. Disinfectant
Potassium permanganate (KMnO₄) is used as a disinfectant to kill bacteria.
📌 Final Answer:
Salts are widely used as fertilizers, pesticides, medicines, antacids, disinfectants, plaster casts and X-ray contrast materials, making them essential in daily life.
Q5. Elaborate the Arrhenius concept of acid and base with suitable examples. Why is the Arrhenius concept limited compared to Brønsted–Lowry theory? Which of the following is/are Arrhenius acids and bases?
(a) Ca(OH)₂ (b) HNO₃ (c) NaOH (d) H₂SO₄ (e) KOH
(a) Ca(OH)₂ (b) HNO₃ (c) NaOH (d) H₂SO₄ (e) KOH
Answer
🧪 Arrhenius Concept of Acids and Bases
Svante Arrhenius proposed a theory of acids and bases according to which:
• An acid is a substance that produces H⁺ ions in aqueous solution.
• A base is a substance that produces OH⁻ ions in aqueous solution.
⚗️ Examples of Arrhenius Acids
The acidic properties of acids are due to the presence of H⁺ ions.
General Acid:
HY(aq) → H⁺(aq) + Y⁻(aq)
Hydrochloric Acid:
HCl(aq) → H⁺(aq) + Cl⁻(aq)
Nitric Acid:
HNO₃(aq) → H⁺(aq) + NO₃⁻(aq)
⚗️ Examples of Arrhenius Bases
The basic properties of bases are due to the presence of OH⁻ ions.
General Base:
MOH(aq) → M⁺(aq) + OH⁻(aq)
Sodium Hydroxide:
NaOH(aq) → Na⁺(aq) + OH⁻(aq)
Ammonium Hydroxide:
NH₄OH(aq) → NH₄⁺(aq) + OH⁻(aq)
⚠️ Limitations of Arrhenius Concept
The Arrhenius concept is limited compared to the Brønsted–Lowry theory because:
1. It is applicable only to aqueous solutions.
2. It cannot explain the basic nature of NH₃ and the acidic nature of CO₂ and similar compounds.
3. Free H⁺ ions do not exist in water; they combine with water molecules to form H₃O⁺ ions.
Therefore, the Brønsted–Lowry theory is more general because it explains acid-base reactions in terms of proton transfer.
✅ Identifying Arrhenius Acids and Bases
(a) Ca(OH)₂ → Arrhenius Base
(b) HNO₃ → Arrhenius Acid
(c) NaOH → Arrhenius Base
(d) H₂SO₄ → Arrhenius Acid
(e) KOH → Arrhenius Base
📌 Final Answer:
According to Arrhenius, acids produce H⁺ ions and bases produce OH⁻ ions in water. The concept is limited because it applies only to aqueous solutions and cannot explain all acid-base reactions. Among the given compounds, HNO₃ and H₂SO₄ are Arrhenius acids, while Ca(OH)₂, NaOH and KOH are Arrhenius bases.
Q6. A solution of HCl has pH of 2.3. Calculate its pOH and [H⁺]?
Solution
Calculation of pOH
pH + pOH = 14 ⇒ pH = 14 − pOH ⇒ pOH = 14 − 2.3 = 11.7
Calculation of [H⁺]
pH = − log [H⁺] ⇒ 10ˣ = [H⁺] ⇒ 10−pH = [H⁺] ⇒ 10−2.3 ⇒ [H⁺] = 5.01 x 10−3
Alternate Method
pH of solution = − log [H⁺]
log [H⁺] = − pH of solution = − 2.3 (On rearranging the equation)
Since exponent should be the whole number, we add and subtract the whole number that is closest to and larger than the negative log.
log [H⁺] = − 2.3 = (−2.3 + 3) − 3 = (0.7 − 3)
Taking antilog on both sides
[H⁺] = antilog (0.7 − 3)
[H⁺] = antilog 0.7 x antilog − 3
[H⁺] = 5.01 x 10−3
[H⁺] = 5.01 x 10−3
Q7. Find pH, pOH, [OH⁻] and [H⁺] of 2.46 x 10⁻⁹ M KOH solution. (Book)
Answer
Solution
Ionization Equation
KOH
⇌
K+
+
OH−
2.46 x 10−9 M 2.46 x 10−9 M 2.46 x 10−9 M
2.46 x 10−9 M 2.46 x 10−9 M 2.46 x 10−9 M
Calculation of [OH−]
Since KOH is strong base, it is completely ionized. Hence concentration of KOH is equal to concentration of OH− ions
[OH−] = [KOH] = 2.46 x 10−9 M
Calculation of [H+]
[H+][OH−] = Kw ⇒ [H+] x 2.46 x 10−9 = 1 x 10−14 ⇒
[H+] = 1 x 10−14 / 2.46 x 10−9 = 4.07 x 10−6
Calculation of pH
pH = − log [H+] = − log [4.07 x 10−6]
= − [log 4.07 + log 10−6] (∵ log ab = log a + log b)
pH = − [0.609 + (−6)] (∵ log 4.07 = 0.609 and log 10−6 = −6) = − [0.609 − 6] = 5.39
Calculation of pOH
pH + pOH = 14 ⇒ pOH = 14 − pH = 14 − 5.39 = 8.61
📘 Extra Solved Numericals on Chapter # 2 (Acids, Bases and Salts)
Prepared by Inam Jazbi – Learn Chemistry
Q1. Calculate the pH and pOH of 0.001 M solution of nitric acid (HNO3).
Solution
Ionization; HNO3(aq) ⇌ H+(aq) + NO3−(aq) (Complete ionization as HNO3 is a strong acid)
1 mol 1 mol 1 mol
[HNO3] = [H+] = 0.001 = 1/1000 = 10−3 M
pH = − log [H+] ⇒ − log [10−3] = − (−3) log 10 = 3 × 1 = 3
pH + pOH = 14 ⇒ pOH = 14 − pH = 14 − 3 = 11
Q2. A solution of hydrochloric acid is 0.01 M. What is its pH value?
Solution
Ionization; HCl(aq) ⇌ H+(aq) + Cl−(aq) (Complete ionization as HCl is a strong acid)
1 mol 1 mol 1 mol
[HCl] = [H+] = 0.01 or 10−2 M
pH = − log [H+] = − log [10−2] = 2
Q3. Find out the pH and pOH of 0.001 M solution of KOH.
Solution
Ionization; KOH(aq) ⇌ K+(aq) + OH−(aq) (Complete ionization as KOH is a strong base)
1 mol 1 mol 1 mol
[KOH] = [OH−] = 0.001 or 1 × 10−3 M
pOH = − log [OH−] ⇒ − log [10−3] = 3 = − [log 1 + log 10−3] (∵ log ab = log a + log b)
pOH = − [0 + (−3)] (∵ log 1 = 0 and log 10−3 = −3) = − [0 − 3] = 3
pH + pOH = 14 ⇒ pH = 14 − pOH = 14 − 3 = 11
📘 Multiple Choice Questions (MCQs) of Acids bases and salts from Text Book (Click to Reveal Answer)
Prepared by Inam Jazbi – Learn Chemistry
1. Corrosive effect on skin is caused by
🟥 (a) Acid
🟦 (b) Base
🟩 (c) Salt
🟨 (d) Both a and b
✔ Correct Answer: 🟨 (d)
Reason: Both strong acids and strong bases are corrosive and can damage skin tissues.
Reason: Both strong acids and strong bases are corrosive and can damage skin tissues.
2. Preservatives are used to preserve
🟥 (a) Acid
🟦 (b) Base
🟩 (c) Food
🟨 (d) Water
✔ Correct Answer: 🟩 (c)
Short Reason: Preservatives are added to prevent spoilage of food.
Short Reason: Preservatives are added to prevent spoilage of food.
3. Which of the following is NOT an Arrhenius acid?
🟥 (a) HCl
🟦 (b) CO₂
🟩 (c) HNO₃
🟨 (d) H₂SO₄
✔ Correct Answer: 🟦 (b)
Short Reason: CO₂ is an acidic oxide, not an Arrhenius acid itself.
Short Reason: CO₂ is an acidic oxide, not an Arrhenius acid itself.
4. NH₃ can be a base according to
🟥 (a) Arrhenius theory
🟦 (b) Brønsted-Lowry theory
🟩 (c) Lewis theory
🟨 (d) both b and c
✔ Correct Answer: 🟨 (d)
Short Reason: NH₃ acts as a proton acceptor and electron pair donor.
Short Reason: NH₃ acts as a proton acceptor and electron pair donor.
5. Which of the following is a Lewis base?
🟥 (a) HNO₃
🟦 (b) CN⁻
🟩 (c) HCl
🟨 (d) AlCl₃
✔ Correct Answer: 🟦 (b)
Short Reason: CN⁻ donates an electron pair, so it acts as a Lewis base.
Short Reason: CN⁻ donates an electron pair, so it acts as a Lewis base.
6. A substance that can donate a pair of electrons to form coordinate covalent bond
🟥 (a) Brønsted-Lowry base
🟦 (b) Brønsted-Lowry acid
🟩 (c) Lewis acid
🟨 (d) Lewis base
✔ Correct Answer: 🟨 (d)
Short Reason: Lewis base donates an electron pair to form a coordinate bond.
Short Reason: Lewis base donates an electron pair to form a coordinate bond.
7. If pH value is greater than 7, then solution is
🟥 (a) acidic
🟦 (b) basic
🟩 (c) amphoteric
🟨 (d) neutral
✔ Correct Answer: 🟦 (b)
Short Reason: pH greater than 7 indicates alkaline (basic) nature.
Short Reason: pH greater than 7 indicates alkaline (basic) nature.
8. Salt among the following is
🟥 (a) HCl
🟦 (b) KCl
🟩 (c) HNO₃
🟨 (d) H₂SO₄
✔ Correct Answer: 🟦 (b)
Short Reason: KCl is a salt formed from acid and base neutralization.
Short Reason: KCl is a salt formed from acid and base neutralization.
9. Substance that reacts with both acids and bases are called
🟥 (a) Amphoteric substances
🟦 (b) Conjugate acids
🟩 (c) Conjugate bases
🟨 (d) Buffers
✔ Correct Answer: 🟨 (a)
Short Reason: Amphoteric substances can act as both acid and base.
Short Reason: Amphoteric substances can act as both acid and base.
10. The reaction of acid and base to form salt and water is called
🟥 (a) Hydration
🟦 (b) Neutralization
🟩 (c) Hydrolysis
🟨 (d) both a and c
✔ Correct Answer: 🟦 (b)
Short Reason: Acid and base react to form salt and water in neutralization reaction.
Short Reason: Acid and base react to form salt and water in neutralization reaction.
11. Which of the following is a strong acid?
🟥 (a) CH₃COOH
🟦 (b) HCl
🟩 (c) NH₄OH
🟨 (d) H₂O
✔ Correct Answer: 🟦 (b)
Short Reason: HCl completely ionizes in water, so it is a strong acid.
Short Reason: HCl completely ionizes in water, so it is a strong acid.
12. Which of the following is a base?
🟥 (a) NaCl
🟦 (b) NaOH
🟩 (c) HCl
🟨 (d) H₂SO₄
✔ Correct Answer: 🟦 (b)
Short Reason: NaOH releases OH⁻ ions in water, so it is a base.
Short Reason: NaOH releases OH⁻ ions in water, so it is a base.
13. Which of the following is a neutral salt?
🟥 (a) NH₄Cl
🟦 (b) NaCl
🟩 (c) CH₃COONa
🟨 (d) NH₄OH
✔ Correct Answer: 🟦 (b)
Short Reason: NaCl is formed from strong acid and strong base, so it is neutral.
Short Reason: NaCl is formed from strong acid and strong base, so it is neutral.
14. A solution with pH = 2 is:
🟥 (a) basic
🟦 (b) acidic
🟩 (c) neutral
🟨 (d) amphoteric
✔ Correct Answer: 🟦 (b)
Short Reason: pH less than 7 indicates acidic solution.
Short Reason: pH less than 7 indicates acidic solution.
15. Which gas is released when acid reacts with metal?
🟥 (a) Oxygen
🟦 (b) Hydrogen
🟩 (c) Carbon dioxide
🟨 (d) Nitrogen
✔ Correct Answer: 🟦 (b)
Short Reason: Acid reacts with metal to produce hydrogen gas.
Short Reason: Acid reacts with metal to produce hydrogen gas.
16. Which of the following is a weak acid?
🟥 (a) HCl
🟦 (b) HNO₃
🟩 (c) CH₃COOH
🟨 (d) H₂SO₄
✔ Correct Answer: 🟩 (c)
Short Reason: Acetic acid partially ionizes in water, so it is a weak acid.
Short Reason: Acetic acid partially ionizes in water, so it is a weak acid.
17. Which indicator turns red in acidic solution?
🟥 (a) Phenolphthalein
🟦 (b) Litmus
🟩 (c) Methyl orange
🟨 (d) All of these
✔ Correct Answer: 🟩 (c)
Short Reason: Methyl orange turns red in acidic medium.
Short Reason: Methyl orange turns red in acidic medium.
18. Which of the following is a basic salt?
🟥 (a) NaCl
🟦 (b) Na₂CO₃
🟩 (c) KNO₃
🟨 (d) HCl
✔ Correct Answer: 🟦 (b)
Short Reason: Na₂CO₃ is formed from strong base and weak acid, so it is basic.
Short Reason: Na₂CO₃ is formed from strong base and weak acid, so it is basic.
19. Which of the following increases pH of a solution?
🟥 (a) Adding acid
🟦 (b) Adding base
🟩 (c) Adding salt
🟨 (d) Adding water only
✔ Correct Answer: 🟦 (b)
Short Reason: Bases increase hydroxide ions, raising pH.
Short Reason: Bases increase hydroxide ions, raising pH.
20. Which of the following is used to test acids and bases?
🟥 (a) Oxygen gas
🟦 (b) Litmus paper
🟩 (c) Salt
🟨 (d) Sugar solution
✔ Correct Answer: 🟦 (b)
Short Reason: Litmus paper changes color in acids and bases.
Short Reason: Litmus paper changes color in acids and bases.
21. pH is defined as:
🟥 (a) negative log of OH⁻
🟦 (b) negative log of H⁺
🟩 (c) positive log of H⁺
🟨 (d) positive log of OH⁻
✔ Correct Answer: 🟦 (b)
Short Reason: pH = -log[H⁺].
Short Reason: pH = -log[H⁺].
22. pOH of a solution is defined as:
🟥 (a) -log[H⁺]
🟦 (b) -log[OH⁻]
🟩 (c) log[OH⁻]
🟨 (d) log[H⁺]
✔ Correct Answer: 🟦 (b)
Short Reason: pOH = -log[OH⁻].
Short Reason: pOH = -log[OH⁻].
23. The sum of pH and pOH at 25°C is:
🟥 (a) 14
🟦 (b) 7
🟩 (c) 1
🟨 (d) 10
✔ Correct Answer: 🟥 (a)
Short Reason: pH + pOH = 14 at 25°C.
Short Reason: pH + pOH = 14 at 25°C.
24. Kw represents:
🟥 (a) equilibrium constant of water
🟦 (b) ionic product of water
🟩 (c) acidity of water
🟨 (d) basicity of water
✔ Correct Answer: 🟦 (b)
Short Reason: Kw is the ionic product of water = [H⁺][OH⁻].
Short Reason: Kw is the ionic product of water = [H⁺][OH⁻].
25. At 25°C, the value of Kw is:
🟥 (a) 1 × 10⁻⁷
🟦 (b) 1 × 10⁻¹⁴
🟩 (c) 1 × 10⁻¹⁰
🟨 (d) 1 × 10⁻⁵
✔ Correct Answer: 🟦 (b)
Short Reason: Kw of water at 25°C is 1 × 10⁻¹⁴.
Short Reason: Kw of water at 25°C is 1 × 10⁻¹⁴.
26. If [H⁺] = 1 × 10⁻³ M, the pH of solution is:
🟥 (a) 1
🟦 (b) 3
🟩 (c) 11
🟨 (d) 7
✔ Correct Answer: 🟦 (b)
Short Reason: pH = -log(10⁻³) = 3.
Short Reason: pH = -log(10⁻³) = 3.
27. If pH = 9, then pOH will be:
🟥 (a) 3
🟦 (b) 5
🟩 (c) 7
🟨 (d) 14
✔ Correct Answer: 🟥 (a)
Short Reason: pOH = 14 − pH = 14 − 9 = 5.
Short Reason: pOH = 14 − pH = 14 − 9 = 5.
28. A solution has pOH = 2. Its pH is:
🟥 (a) 12
🟦 (b) 10
🟩 (c) 7
🟨 (d) 2
✔ Correct Answer: 🟥 (a)
Short Reason: pH = 14 − pOH = 12.
Short Reason: pH = 14 − pOH = 12.
29. If [OH⁻] = 1 × 10⁻⁵ M, the pOH is:
🟥 (a) 5
🟦 (b) 9
🟩 (c) 7
🟨 (d) 3
✔ Correct Answer: 🟥 (a)
Short Reason: pOH = -log(10⁻⁵) = 5.
Short Reason: pOH = -log(10⁻⁵) = 5.
30. In pure water at 25°C, [H⁺] is:
🟥 (a) 1 × 10⁻⁷ M
🟦 (b) 1 × 10⁻¹⁴ M
🟩 (c) 1 × 10⁻⁵ M
🟨 (d) 7 × 10⁻¹ M
✔ Correct Answer: 🟥 (a)
Short Reason: Neutral water has [H⁺] = 10⁻⁷ M at 25°C.
Short Reason: Neutral water has [H⁺] = 10⁻⁷ M at 25°C.