Class 10 : Science (In English) – Lesson 2. Acids, Bases and Salts

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On June 20, 2025

EXPLANATION & SUMMARY

The chapter “Acids, Bases and Salts” from Class 10 Science introduces students to one of the most important topics in chemistry. Acids and bases are substances that we come across in everyday life — in food, cleaning agents, medicines, and even in nature. This lesson explains their chemical properties, reactions, the concept of pH, and the formation and utility of salts.

What are Acids and Bases?

Acids are substances that release hydrogen ions (H⁺) in aqueous solutions. They are sour in taste and turn blue litmus red.
Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Citric acid (in lemons), Acetic acid (in vinegar).

Bases are substances that release hydroxide ions (OH⁻) in aqueous solutions. They are bitter in taste and soapy to touch. They turn red litmus blue.
Examples: Sodium hydroxide (NaOH), Magnesium hydroxide (Mg(OH)₂), Ammonium hydroxide (NH₄OH).
Some bases are soluble in water – these are called alkalis.

Classification of Acids and Bases
Acids:
Strong acids: Completely ionize in water (e.g., HCl, H₂SO₄)
Weak acids: Partially ionize in water (e.g., CH₃COOH)
Bases:
Strong bases: Completely ionize in water (e.g., NaOH, KOH)
Weak bases: Partially ionize (e.g., NH₄OH)

Indicators
Indicators are substances that change color in acidic or basic medium and help identify the nature of a solution.
Common Indicators:
Litmus: Blue in base, red in acid.
Methyl Orange: Red in acid, yellow in base.
Phenolphthalein: Colorless in acid, pink in base.
Natural indicators: Red cabbage juice, turmeric, etc.

Chemical Properties of Acids and Bases

Reaction with Metals
Acid + Metal → Salt + Hydrogen gas
Zn + H₂SO₄ → ZnSO₄ + H₂↑
Base + Metal → Salt + Hydrogen gas (only with amphoteric metals like Al, Zn)
2Al + 2NaOH + 6H₂O → 2Na[Al(OH)₄] + 3H₂↑

Reaction with Metal Carbonates and Bicarbonates
Acid + Metal Carbonate → Salt + CO₂ + H₂O
HCl + Na₂CO₃ → 2NaCl + CO₂ + H₂O
Acid + Metal Bicarbonate → Salt + CO₂ + H₂O
HCl + NaHCO₃ → NaCl + CO₂ + H₂O
Carbon dioxide released turns lime water milky.
Reaction with Bases (Neutralization)

Acid + Base → Salt + Water
HCl + NaOH → NaCl + H₂O
This is a neutralization reaction, producing a neutral product.
Reaction with Oxides

Acids react with metal oxides (basic):
2HCl + CuO → CuCl₂ + H₂O
Bases react with non-metal oxides (acidic):
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
This proves that metal oxides are basic and non-metal oxides are acidic in nature.

How Strong are Acid or Base Solutions?
Strength of an acid or base is measured using the pH scale (Potential of Hydrogen), ranging from 0 to 14.
pH < 7: Acidic
pH = 7: Neutral
pH > 7: Basic
Lower the pH, stronger the acid; higher the pH, stronger the base.
Examples:
Stomach acid (HCl): pH ≈ 1.2
Lemon juice: pH ≈ 2.5
Pure water: pH = 7
Soap: pH ≈ 9
NaOH solution: pH ≈ 13
The pH of a solution affects living organisms. Human blood, for instance, maintains a pH around 7.4.

Importance of pH in Everyday Life
In Plants and Animals: pH stability is crucial. Enzyme activity and cell functions occur within narrow pH ranges.
In Soil: Acidic or basic soils affect plant growth. Farmers use lime (CaO) to neutralize acidic soil.
In Medicine: pH of the stomach (very acidic) aids digestion. Antacids like Mg(OH)₂ neutralize excess acid.
In Tooth Decay: Bacteria produce acids after eating sugary foods, lowering pH. Tooth enamel dissolves below pH 5.5.
In Industry: Acid-base reactions are used in textile, dye, and chemical industries for pH control.

Salts

Salts are ionic compounds formed during neutralization reactions between acids and bases.
General Formula:
Acid + Base → Salt + Water
Example:
HCl + NaOH → NaCl + H₂O
Salts can be:
Neutral (e.g., NaCl)
Acidic (e.g., NH₄Cl)
Basic (e.g., Na₂CO₃)

Important Salts and Their Uses
Sodium Chloride (NaCl) – Common Salt
Essential in diet, used in cooking and food preservation.
Raw material for making:
Sodium hydroxide (NaOH)
Baking soda (NaHCO₃)
Washing soda (Na₂CO₃)
Bleaching powder (Ca(OCl)₂)

Sodium Hydroxide (NaOH) – Caustic Soda
Produced by electrolysis of brine (NaCl solution).
Used in making soaps, detergents, paper, synthetic fibers.
Baking Soda (NaHCO₃) – Sodium Bicarbonate
Mild base; used in cooking to make food fluffy.
Reacts with acids to release CO₂: NaHCO₃ + H⁺ → Na⁺ + CO₂ + H₂O
Also used in antacids and fire extinguishers.

Washing Soda (Na₂CO₃·10H₂O)
Prepared from baking soda through heating and recrystallization.
Used in washing clothes, glass, and paper industries.
Removes hardness of water.
Bleaching Powder (Ca(OCl)₂)
Made by reacting chlorine with dry slaked lime: Ca(OH)₂ + Cl₂ → Ca(OCl)₂ + H₂O
Used for bleaching cotton, disinfecting water, and making chloroform.

Crystals of Water of Crystallization
Some salts contain water molecules attached to their structure, known as water of crystallization.
Examples:
CuSO₄·5H₂O (Blue vitriol)
FeSO₄·7H₂O (Green vitriol)
Na₂CO₃·10H₂O (Washing soda)
When heated, they lose water and their color changes: CuSO₄·5H₂O (blue) → CuSO₄ (white) + 5H₂O

Conclusion

The chapter “Acids, Bases, and Salts” provides a deep insight into the nature and behavior of various chemical substances we interact with daily. Acids and bases are not only part of laboratory chemicals but are found in fruits, cleaning agents, and biological systems. The pH scale helps understand the strength and utility of these substances, and salts formed through neutralization have diverse applications, from cooking to industry.
Understanding the chapter empowers students to link textbook chemistry to real life – from toothpaste pH to the fizz in baking. It builds the foundation for further studies in chemistry and various scientific applications in daily life.

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QUESTIONS FROM TEXTBOOK

Question 1
A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10

Answer: The correct answer is (d) 10. When a solution turns red litmus paper blue, it indicates that the solution is basic in nature. Basic solutions have a pH value greater than 7, and among the given options, only 10 represents a basic pH value. Solutions with pH values of 1, 4, and 5 are all acidic and would turn blue litmus paper red instead.

Question 2
A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl

Answer: The correct answer is (b) HCl. Eggshells contain calcium carbonate (CaCO₃), which reacts with hydrochloric acid to produce carbon dioxide gas. The chemical equation for this reaction is: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The carbon dioxide gas produced turns lime water milky due to the formation of calcium carbonate precipitate. Among the given options, only HCl is an acid that can react with calcium carbonate to produce this effect.

Question 3
10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL

Answer: The correct answer is (d) 16 mL. This is a simple proportion problem based on the neutralization reaction. If 10 mL of NaOH requires 8 mL of HCl for complete neutralization, then 20 mL of the same NaOH solution (which is double the original amount) will require double the amount of HCl, which is 8 × 2 = 16 mL. The ratio of acid to base remains constant for the same solutions.

Question 4
Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic

Answer: The correct answer is (c) Antacid. Indigestion occurs due to the excess production of hydrochloric acid in the stomach. Antacids are medicines that contain mild bases which neutralize the excess acid in the stomach and provide relief from indigestion. Examples of antacids include magnesium hydroxide (milk of magnesia) and sodium hydrogencarbonate (baking soda). Antibiotics fight bacterial infections, analgesics relieve pain, and antiseptics prevent infection, but none of these treat indigestion.

Question 5
Write word equations and then balanced equations for the reaction taking place when –

(a) Dilute sulphuric acid reacts with zinc granules.

Answer:
Word equation: Dilute sulphuric acid + Zinc → Zinc sulphate + Hydrogen gas
Balanced chemical equation: H₂SO₄(aq) + Zn(s) → ZnSO₄(aq) + H₂(g)

(b) Dilute hydrochloric acid reacts with magnesium ribbon.

Answer:
Word equation: Dilute hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen gas
Balanced chemical equation: 2HCl(aq) + Mg(s) → MgCl₂(aq) + H₂(g)

Answer:
Word equation: Dilute sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen gas
Balanced chemical equation: 3H₂SO₄(aq) + 2Al(s) → Al₂(SO₄)₃(aq) + 3H₂(g)

(d) Dilute hydrochloric acid reacts with iron filings.

Answer:
Word equation: Dilute hydrochloric acid + Iron → Ferrous chloride + Hydrogen gas
Balanced chemical equation: 2HCl(aq) + Fe(s) → FeCl₂(aq) + H₂(g)

Question 6
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

Answer: To prove that alcohols and glucose are not acids despite containing hydrogen, we can perform the following activity:

Insert two nails into a wooden or rubber cork and place them in a beaker

Connect the nails to a 6-volt battery through a bulb and a switch

Pour some alcohol or glucose solution into the beaker so that the nails are dipped in the solution

Turn on the switch and observe that the bulb does not glow

Empty the beaker and add dilute HCl solution

Turn on the switch again and observe that the bulb now glows

This experiment demonstrates that acids conduct electricity due to the presence of ions, while alcohols and glucose do not conduct electricity because they do not ionize in solution. Although alcohols and glucose contain hydrogen atoms, these hydrogen atoms do not separate as H⁺ ions when dissolved in water, which is why they do not show acidic properties.

Question 7
Why does distilled water not conduct electricity, whereas rain water does?

Answer: Distilled water does not conduct electricity because it does not contain any ionic compounds. Pure distilled water consists only of H₂O molecules and lacks free ions that are necessary for conducting electric current.

Rain water, on the other hand, conducts electricity because it contains dissolved substances. When rain falls through the atmosphere, it dissolves acidic gases such as carbon dioxide from the air, forming carbonic acid (H₂CO₃). This results in the presence of hydrogen ions (H⁺) and carbonate ions (CO₃²⁻) in rain water. These ions enable rain water to conduct electricity. Additionally, rain water may also dissolve other impurities and salts from the atmosphere, further increasing its ionic content.

Question 8
Why do acids not show acidic behaviour in the absence of water?

Answer: Acids do not show acidic behavior in the absence of water because acidic properties are due to the presence of hydrogen ions (H⁺) in solution. Hydrogen ions can only be produced when acids are dissolved in water. In the absence of water, acid molecules remain intact and do not release H⁺ ions.

For example, dry HCl gas does not change the color of dry litmus paper because it cannot produce H⁺ ions without water. However, when HCl gas comes in contact with moist litmus paper (containing water), it ionizes to produce H⁺ ions and shows acidic behavior by turning blue litmus paper red. The ionization process can be represented as: HCl + H₂O → H₃O⁺ + Cl⁻. Therefore, water is essential for acids to exhibit their characteristic acidic properties.

Question 9
Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.

Answer:
Based on the pH values given:

(a) Neutral: Solution D (pH = 7)

(b) Strongly alkaline: Solution C (pH = 11)

(d) Weakly acidic: Solution A (pH = 4)

(e) Weakly alkaline: Solution E (pH = 9)

Arrangement in increasing order of hydrogen-ion concentration:
pH 11(C) < pH 9(E) < pH 7(D) < pH 4(A) < pH 1(B)

This is because hydrogen ion concentration is inversely proportional to pH value. Lower pH means higher hydrogen ion concentration, and higher pH means lower hydrogen ion concentration.

Question 10
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Answer: The fizzing will occur more vigorously in test tube A containing hydrochloric acid. This is because HCl is a strong acid while acetic acid (CH₃COOH) is a weak acid.

Fizzing occurs due to the production of hydrogen gas when the acid reacts with magnesium ribbon. The reaction can be represented as: Mg + 2H⁺ → Mg²⁺ + H₂. Since HCl is a strong acid, it ionizes completely in solution and produces more H⁺ ions compared to acetic acid, which ionizes only partially. The greater availability of H⁺ ions from HCl results in faster reaction rate and more vigorous production of hydrogen gas. Therefore, more fizzing takes place in test tube A.

Question 11
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Answer: When fresh milk turns into curd, its pH will decrease (become more acidic). Fresh milk has a pH of 6, which is slightly acidic. As milk turns into curd, bacteria present in milk convert lactose (milk sugar) into lactic acid.

The production of lactic acid increases the concentration of H⁺ ions in the solution, which causes the pH to drop further below 6. This increase in acidity is responsible for the sour taste of curd. The bacterial fermentation process continues until enough lactic acid is produced to give curd its characteristic tangy flavor and lower pH.

Question 12
A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?

Answer:
(a) The milkman shifts the pH of fresh milk from 6 to slightly alkaline to prevent the milk from getting sour due to the formation of lactic acid. Fresh milk naturally contains bacteria that can convert lactose into lactic acid, making the milk sour. By adding baking soda (sodium hydrogencarbonate), which is a mild base, he neutralizes any acid that might form initially and makes the milk slightly alkaline. This helps preserve the milk for a longer period and prevents it from spoiling quickly.

(b) This milk takes a long time to set as curd because the alkaline environment created by baking soda is not favorable for the bacterial action required for curd formation. The lactic acid bacteria need a slightly acidic environment to thrive and convert lactose into lactic acid. Since the milk is now alkaline, the bacteria first need to neutralize the alkaline pH by producing enough lactic acid. Only after the pH becomes acidic can the milk start setting into curd. This additional step of neutralizing the alkaline pH significantly increases the time required for curd formation.

Question 13
Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer: Plaster of Paris should be stored in a moisture-proof container because it readily absorbs moisture from the air and hardens. Plaster of Paris has the chemical formula CaSO₄·½H₂O (calcium sulphate hemihydrate).

When Plaster of Paris comes in contact with moisture, it undergoes the following reaction:
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O

This reaction converts Plaster of Paris back into gypsum, forming a hard solid mass. If Plaster of Paris absorbs moisture from the atmosphere, it will set and harden in the container itself, making it impossible to use. Therefore, it must be stored in a moisture-proof container to prevent contact with atmospheric moisture and maintain its usability.

Question 14
What is a neutralisation reaction? Give two examples.

Answer: A neutralization reaction is a chemical reaction between an acid and a base that produces a salt and water. In this reaction, the acidic and basic properties of the reactants are neutralized, forming neutral products. The general equation for a neutralization reaction is:

Acid + Base → Salt + Water

Examples:

Sodium hydroxide + Hydrochloric acid → Sodium chloride + Water
NaOH + HCl → NaCl + H₂O

Magnesium hydroxide + Carbonic acid → Magnesium carbonate + Water
Mg(OH)₂ + H₂CO₃ → MgCO₃ + 2H₂O

In both examples, the acid and base react to form a salt and water, with the H⁺ ions from the acid combining with OH⁻ ions from the base to form water molecules.

Question 15
Give two important uses of washing soda and baking soda.

Answer:

Uses of Washing Soda (Na₂CO₃·10H₂O):

It is used in glass, soap and paper industries as a raw material

It is used for removing permanent hardness of water by precipitating calcium and magnesium ions

Uses of Baking Soda (NaHCO₃):

It is used for making baking powder, which helps bread and cakes to rise by producing carbon dioxide gas when heated

It is used as an ingredient in antacids to neutralize excess acid in the stomach and provide relief from acidity

Both washing soda and baking soda are important chemicals derived from common salt and have numerous applications in household and industrial processes.

[CBSE MODEL QUESTION PAPER]

🔹 1. Multiple Choice Questions (10 Questions × 1 mark = 10 Marks)
Q1. Which of the following will have the highest concentration of H⁺ ions?
A. Lemon juice
B. Soap solution
C. Distilled water
D. Baking soda
Answer: A

Q2. Which of these substances will not change the color of red or blue litmus?
A. Vinegar
B. Sugar solution
C. Soap
D. Lime water
Answer: B

Q3. Which of the following is not a property of a base?
A. Bitter taste
B. Slippery touch
C. Produces H⁺ ions
D. Turns red litmus blue
Answer: C

Q4. The reaction of baking soda with acid produces:
A. H₂
B. O₂
C. CO₂
D. Cl₂
Answer: C

Q5. A salt which forms an alkaline solution in water is:
A. NaCl
B. NH₄Cl
C. Na₂CO₃
D. KNO₃
Answer: C

Q6. Which salt contains water of crystallization?
A. NaCl
B. CuSO₄
C. KNO₃
D. NaOH
Answer: B

Q7. Which of the following is used for softening hard water?
A. Bleaching powder
B. Sodium chloride
C. Washing soda
D. Baking soda
Answer: C

Q8. What happens when CO₂ is passed through lime water for a short time?
A. Turns milky
B. Becomes colorless
C. No change
D. Gives off oxygen
Answer: A

Q9. Which of the following is the correct pH range for an acidic solution?
A. 0–6.9
B. 7.1–14
C. Exactly 7
D. 8–10
Answer: A

Q10. Which of these helps maintain the pH of blood?
A. Sodium bicarbonate
B. Calcium carbonate
C. Ammonia
D. Acetic acid
Answer: A

🔹 2. Fill in the Blanks (3 Questions × 1 mark = 3 Marks)
Q11. The chemical formula of bleaching powder is _.
Answer: Ca(OCl)₂

Q12. The acid produced in the stomach to aid digestion is _.
Answer: Hydrochloric acid (HCl)

Q13. The pH of a neutral solution is _.
Answer: 7

🔹 3. Assertion and Reasoning Questions (3 Questions × 1 mark = 3 Marks)
(Choose: A – Both A and R are true and R explains A, B – Both A and R are true but R does not explain A, C – A is true, R is false, D – A is false, R is true)
Q14.
Assertion (A): The pH of acidic solutions is less than 7.
Reason (R): Acids release hydroxide ions in water.
Answer: C

Q15.
Assertion (A): Toothpaste is basic in nature.
Reason (R): It neutralizes the acid formed in the mouth by bacteria.
Answer: A

Q16.
Assertion (A): Lime water turns milky when CO₂ is passed through it.
Reason (R): CO₂ reacts with Ca(OH)₂ to form CaCO₃, which is insoluble.
Answer: A

🔹 4. Select Right or Wrong (2 Questions × 1 mark = 2 Marks)
(Write “Right” or “Wrong” and justify your answer.)

Q17. All acids contain hydrogen, therefore all hydrogen-containing compounds are acids.
Answer: Wrong. Not all hydrogen-containing compounds release H⁺ ions in water (e.g., CH₄ is not an acid).

Q18. A solution with pH = 9 is more acidic than a solution with pH = 5.
Answer: Wrong. A lower pH indicates higher acidity, so pH 5 is more acidic.

🔹 5. Short Answer Questions (5 Questions × 3 marks = 15 Marks)
(Answer in about 50–70 words each.)

Q19. Why does dry HCl gas not change the color of dry litmus paper, while aqueous HCl does?
Answer: Dry HCl does not produce H⁺ ions as it lacks water. Ionization happens only in aqueous solutions. Since litmus detects H⁺ ions, dry HCl fails to show acidity. Aqueous HCl releases H⁺ ions and changes blue litmus red.

Q20. What is the role of water in the ionization of acids and bases?
Answer: Water acts as a medium in which acids and bases dissociate to release H⁺ and OH⁻ ions respectively. Without water, ionization does not occur, and the substances don’t exhibit their acidic or basic properties.

Q21. How does the pH of soil affect the growth of plants? How can we correct the soil pH?
Answer: Most plants grow best at neutral or slightly acidic pH. If soil is too acidic, growth is hindered. Acidic soil can be corrected using bases like slaked lime (Ca(OH)₂). Similarly, basic soils can be corrected by adding organic matter or mild acids.

Q22. Give one practical application of neutralization in daily life.
Answer: Antacids like magnesium hydroxide neutralize excess stomach acid (HCl), giving relief from acidity or heartburn. This is a neutralization reaction:
Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Q23. How is baking soda used in baking and fire extinguishers?
Answer: In baking, baking soda (NaHCO₃) releases CO₂ when heated with acids, making dough rise. In fire extinguishers, CO₂ released from reaction of baking soda with acid blankets the fire and cuts off oxygen supply.

🔹 6. Long Answer Questions (2 Questions × 5 marks = 10 Marks)
(Answer in about 120–150 words each.)

Q24. Explain the preparation and uses of bleaching powder. Also write the chemical equation involved.
Answer: Bleaching powder (Ca(OCl)₂) is prepared by passing chlorine gas over dry slaked lime:
Ca(OH)₂ + Cl₂ → Ca(OCl)₂ + H₂O
It is a white powder with a strong smell of chlorine. It is used for:
Disinfecting drinking water
Bleaching cotton and linen in the textile industry
Used as an oxidizing agent in chemical industries
Used in making chloroform
It is a powerful disinfectant and is commonly stored in dark containers to prevent decomposition.

Q25. Describe the chemical properties of acids with suitable examples and equations.
Answer:
With Metals: Produces salt and hydrogen gas
Zn + 2HCl → ZnCl₂ + H₂↑
With Metal Carbonates/Bicarbonates: Produces salt, CO₂, and water
Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
With Bases (Neutralization):
HCl + NaOH → NaCl + H₂O
With Metal Oxides: Forms salt and water
2HCl + CuO → CuCl₂ + H₂O
These reactions demonstrate acids’ ability to donate H⁺ ions and their reactive nature toward metals, bases, and carbonates.

QUESTIONS FROM COMPETITIONS EXAMS

🔵 Question 1:
Which of the following is an acid?
(A) Sodium hydroxide
(B) Ammonia
(C) Hydrochloric acid
(D) Calcium hydroxide
✅ Correct Answer: (C) Hydrochloric acid
📄 Exam: SSC CGL 2017

🟢 Question 2:
Which of these substances turns red litmus blue?
(A) Lemon juice
(B) Vinegar
(C) Baking soda solution
(D) Carbonated water
✅ Correct Answer: (C) Baking soda solution
📄 Exam: NDA 2016

🔴 Question 3:
Which is a neutral substance among the following?
(A) Pure water
(B) Lemon juice
(C) Sodium hydroxide
(D) Vinegar
✅ Correct Answer: (A) Pure water
📄 Exam: RRB ALP 2018

🟡 Question 4:
Common salt is chemically known as:
(A) Sodium bicarbonate
(B) Sodium chloride
(C) Sodium carbonate
(D) Potassium chloride
✅ Correct Answer: (B) Sodium chloride
📄 Exam: IBPS Clerk 2019

🔵 Question 5:
Which gas is released when dilute hydrochloric acid reacts with zinc?
(A) Hydrogen
(B) Oxygen
(C) Nitrogen
(D) Carbon dioxide
✅ Correct Answer: (A) Hydrogen
📄 Exam: SSC CHSL 2018

🟢 Question 6:
Which acid is present in vinegar?
(A) Hydrochloric acid
(B) Acetic acid
(C) Citric acid
(D) Sulphuric acid
✅ Correct Answer: (B) Acetic acid
📄 Exam: UPPSC PCS 2020

🔴 Question 7:
The nature of lime water is:
(A) Acidic
(B) Basic
(C) Neutral
(D) Amphoteric
✅ Correct Answer: (B) Basic
📄 Exam: SSC GD 2021

🟡 Question 8:
Which salt is used to remove permanent hardness of water?
(A) Baking soda
(B) Washing soda
(C) Common salt
(D) Potash alum
✅ Correct Answer: (B) Washing soda
📄 Exam: SBI PO 2017

🔵 Question 9:
Which of the following indicators is natural?
(A) Methyl orange
(B) Phenolphthalein
(C) Litmus
(D) Methyl red
✅ Correct Answer: (C) Litmus
📄 Exam: SSC MTS 2020

🟢 Question 10:
Which acid is produced in our stomach?
(A) Acetic acid
(B) Sulphuric acid
(C) Hydrochloric acid
(D) Nitric acid
✅ Correct Answer: (C) Hydrochloric acid
📄 Exam: CDS 2019

🔴 Question 11:
What is the pH value of pure water?
(A) 4
(B) 5
(C) 7
(D) 9
✅ Correct Answer: (C) 7
📄 Exam: AFCAT 2020

🟡 Question 12:
Which of the following substances is alkaline in nature?
(A) Vinegar
(B) Soap solution
(C) Lemon juice
(D) Carbonated water
✅ Correct Answer: (B) Soap solution
📄 Exam: SSC JE 2022

🔵 Question 13:
Plaster of Paris is chemically known as:
(A) Calcium carbonate
(B) Calcium oxide
(C) Calcium sulphate hemihydrate
(D) Calcium chloride
✅ Correct Answer: (C) Calcium sulphate hemihydrate
📄 Exam: RRB JE 2019

🟢 Question 14:
Which of the following can neutralize an acid?
(A) Vinegar
(B) Water
(C) Baking soda
(D) Citric acid
✅ Correct Answer: (C) Baking soda
📄 Exam: SSC CGL 2016

🔴 Question 15:
Which of the following is used in antacid tablets?
(A) Sodium chloride
(B) Sodium bicarbonate
(C) Calcium chloride
(D) Potassium nitrate
✅ Correct Answer: (B) Sodium bicarbonate
📄 Exam: NDA 2017

🟡 Question 16:
Which is a weak acid?
(A) Hydrochloric acid
(B) Nitric acid
(C) Acetic acid
(D) Sulphuric acid
✅ Correct Answer: (C) Acetic acid
📄 Exam: SSC CPO 2020

🔵 Question 17:
Which of the following is formed when an acid reacts with a base?
(A) Salt
(B) Water
(C) Both salt and water
(D) Hydrogen gas
✅ Correct Answer: (C) Both salt and water
📄 Exam: CAPF 2019

🟢 Question 18:
Which of the following is not acidic?
(A) Orange juice
(B) Tomato
(C) Milk of magnesia
(D) Vinegar
✅ Correct Answer: (C) Milk of magnesia
📄 Exam: SSC CHSL 2021

🔴 Question 19:
Which of these turns blue litmus red?
(A) Soap solution
(B) Baking soda solution
(C) Lemon juice
(D) Milk
✅ Correct Answer: (C) Lemon juice
📄 Exam: IBPS PO 2016

🟡 Question 20:
Tartaric acid is present in:
(A) Apple
(B) Grapes
(C) Tamarind
(D) Milk
✅ Correct Answer: (C) Tamarind
📄 Exam: SSC JE 2018

🔵 Question 21:
The formula of baking soda is:
(A) Na₂CO₃
(B) NaHCO₃
(C) NaOH
(D) NaCl
✅ Correct Answer: (B) NaHCO₃
📄 Exam: CDS 2021

🟢 Question 22:
Which of the following gives CO₂ with dilute acid?
(A) CaCO₃
(B) NaOH
(C) KOH
(D) CaCl₂
✅ Correct Answer: (A) CaCO₃
📄 Exam: NDA 2019

🔴 Question 23:
Blue vitriol is:
(A) CuSO₄·5H₂O
(B) FeSO₄
(C) Na₂CO₃
(D) MgSO₄
✅ Correct Answer: (A) CuSO₄·5H₂O
📄 Exam: SSC GD 2020

🟡 Question 24:
Which one is not a salt?
(A) NaCl
(B) Na₂CO₃
(C) NaHCO₃
(D) HCl
✅ Correct Answer: (D) HCl
📄 Exam: SSC CGL 2022

🔵 Question 25:
What is the chemical name of gypsum?
(A) Calcium sulphate dihydrate
(B) Calcium sulphate hemihydrate
(C) Calcium carbonate
(D) Calcium oxide
✅ Correct Answer: (A) Calcium sulphate dihydrate
📄 Exam: SSC MTS 2019

ONE PAGE REVISISON SHEET

Acids:
Acids are sour in taste and turn blue litmus red.
They release H⁺ ions in aqueous solutions.
Types:
Mineral Acids: HCl, H₂SO₄, HNO₃
Organic Acids: Citric acid, Acetic acid
Strong acids: Completely ionize (e.g., HCl)
Weak acids: Partially ionize (e.g., CH₃COOH)

Bases:
Bitter in taste, soapy to touch, turn red litmus blue.
They release OH⁻ ions in aqueous solutions.
Examples: NaOH, KOH, Ca(OH)₂
Water soluble bases are called alkalis.
Indicators:
Used to identify acids and bases.
Litmus: Acid → Red, Base → Blue
Methyl orange: Acid → Red, Base → Yellow
Phenolphthalein: Acid → Colourless, Base → Pink

Reactions of Acids and Bases:
Neutralization:
Acid + Base → Salt + Water
e.g., HCl + NaOH → NaCl + H₂O
Reaction with metal:
Acid + Metal → Salt + H₂ gas
Base + Metal → Salt + H₂ gas (less reactive metals)
Reaction with metal carbonate/hydrogencarbonate:
Acid + Metal carbonate → Salt + CO₂ + H₂O

Salts:
Formed by reaction of acids and bases.
Can be neutral, acidic, or basic in nature.
Examples: NaCl, (NH₄)₂SO₄, CH₃COONa
Family of salts: Common cation or anion
Used in food, industry, and daily life.
pH Scale:
Ranges from 0 to 14
<7: Acidic, =7: Neutral, >7: Basic
Universal indicator shows exact pH value.
Common Salts and Their Uses:
NaCl: Table salt
Baking soda (NaHCO₃): Used in baking
Washing soda (Na₂CO₃): Cleaning agent
Plaster of Paris (CaSO₄·½H₂O): Used in casts, sculptures