Extra 20 long-answer questions for Chapter:2 Acids, Bases, and Salts from Class 10 CBSE Science.
1. Define acids and bases. Explain their physical and chemical properties with examples.
Answer:
Acids
: Substances that release
H⁺ ions
in solution. Example:
HCl, H₂SO₄
.
Bases
: Substances that release
OH⁻ ions
in solution. Example:
NaOH,
Ca(
OH)₂
.
Physical Properties of Acids
:
Sour taste
Turns blue litmus red
Conducts electricity in aqueous solution
Physical Properties of Bases
:
4. Bitter taste
5. Turns red litmus blue
6. Feels slippery
Chemical Properties
:
7. Acids react with metals to form
H₂ gas
8. Bases react with acids to form
salt and water
(Neutralization reaction)
2. What are indicators? Explain different types with examples and their uses.
Answer:
Indicators
: Substances that change
colour
based on
pH.
Types of Indicators
:
Natural Indicators
: Litmus (Acid:
red
, Base:
blue
)
Synthetic Indicators
: Methyl orange (Acid:
red
, Base:
yellow
)
Olfactory Indicators
: Onion, vanilla (Smell changes in bases)
Universal Indicator
: Measures
exact pH
using
color
changes.
Uses
:
5. Testing pH in laboratories.
6. Checking soil acidity for farming.
7. Monitoring acid rain impact.
3. What is the pH scale? How does pH affect daily life?
Answer:
pH scale measures acidity/basicity
(0-14).
Acidic (pH < 7)
,
Neutral (pH = 7)
,
Basic (pH > 7)
.
Daily Life Applications
:
Stomach acid (pH 1.5-3.5)
helps digestion.
Tooth decay (pH < 5.5)
causes enamel erosion.
Soil pH
affects plant growth.
Acid rain (pH < 5.6)
damages buildings and crops.
Aquatic life
requires neutral water
pH.
Antacids (pH > 7)
neutralize excess stomach acid.
4. What happens when acids react with metals, metal oxides, and carbonates? Give examples.
Answer:
Acid + Metal → Salt + Hydrogen gas
Example
: Zn+2HCl→ZnCl2+H2↑Zn + 2HCl → ZnCl_2 + H_2↑Zn+2HCl→ZnCl2+H2↑
Acid + Metal Oxide → Salt + Water
Example
: CuO+H2SO4→CuSO4+H2OCuO + H_2SO_4 → CuSO_4 + H_2OCuO+H2SO4→CuSO4+H2O
Acid + Metal Carbonate → Salt + CO₂ + Water
Example
: Na2CO3+2HCl→2NaCl+CO2+H2ONa_2CO_3 + 2HCl → 2NaCl + CO_2 + H_2ONa2CO3+2HCl→2NaCl+CO2+H2O
Hydrogen gas test
: Burning matchstick produces a
pop sound
.
CO₂ gas test
: Turns
lime water milky
.
5. Explain neutralization reactions with examples and applications.
Answer:
Definition
: Acid + Base → Salt + Water
Examples
:
HCl + NaOH → NaCl + H₂O
H₂SO₄ +
Ca(
OH)₂ →
CaSO
₄ + 2H₂O
Applications
:
3.
Antacids
neutralize stomach acid.
4.
Lime (
Ca(
OH)₂) is used in soil
to reduce acidity.
5.
Factory waste
is neutralized before disposal.
6. Explain the preparation of common salt (NaCl) and its uses.
Answer:
Seawater evaporation
leaves behind salt.
Purification
removes impurities.
Uses
:
Food seasoning.
Preservative.
Making caustic soda.
7. What is bleaching powder? How is it prepared? Give its uses.
Answer:
Formula
:
CaOCl
₂
Preparation
:
Ca(
OH)2+Cl2→CaOCl2+H2OCa(OH)_2 + Cl_2 → CaOCl_2 + H_2OCa(OH)2+Cl2→CaOCl2+H2O
Uses
:
Water purification.
Bleaching fabrics.
8. What is baking soda? How is it prepared? Write its uses.
Answer:
Formula
:
NaHCO
₃
Uses
:
Baking.
Fire extinguishers.
9. What is washing soda? Write its uses.
Answer:
Formula
:
Na₂CO
₃·10H₂O
Uses
:
Glass manufacturing.
Softening water.
10. What is Plaster of Paris? How is it prepared? Write its uses.
Answer:
Formula
:
CaSO
₄·½H₂O
Uses
:
Medical bandages.
Making statues.
11. Explain how antacids work with the help of equations.
Answer:
Antacids
are substances that
neutralize excess stomach acid (HCl)
and provide relief from acidity and heartburn.
Examples of antacids
:
Magnesium hydroxide (Milk of Magnesia)
Aluminium
hydroxide
Sodium bicarbonate (Baking soda)
Chemical Equations:
Magnesium hydroxide reaction:
Mg(
OH)2+2HCl→MgCl2+2H2OMg(OH)_2 + 2HCl → MgCl_2 + 2H_2OMg(OH)2+2HCl→MgCl2+2H2O
Sodium bicarbonate reaction:
NaHCO3+HCl→NaCl+CO2+H2ONaHCO_3 + HCl → NaCl + CO_2 + H_2ONaHCO3+HCl→NaCl+CO2+H2O
Uses of Antacids:
Used in medicines for
acid reflux and indigestion
.
Provides relief from
ulcers and gastritis
.
Used in
first-aid treatments
for acid burns.
12. Why is water pH important for aquatic life?
Answer:
Water pH
affects the survival of
fish, plants, and microorganisms
in water bodies.
Ideal pH for aquatic life
: 6.5 to 8.5
Effects of low pH (Acidic water)
:
Kills fish
and aquatic plants.
Dissolves toxic metals
from rocks and pipes, contaminating water.
Leads to
acid rain
, which lowers the pH of lakes and rivers.
Effects of high pH (Basic water)
:
4. Reduces
oxygen solubility
, suffocating fish.
5. Promotes
excessive algae growth
(Eutrophication).
6. Hardens fish scales and
damages gills
.
13. How do bases react with ammonium salts? Give an example.
Answer: Reaction of Bases with Ammonium Salts
When a
base
reacts with an
ammonium salt
, it produces
ammonia gas (NH₃)
, along with
water and a salt
.
This is an example of a
neutralization reaction
, where the base removes
H⁺ ions
from the ammonium salt, releasing ammonia gas.
Example: Reaction of Ammonium Chloride (NH₄Cl) with Sodium Hydroxide (NaOH)
NH4Cl+NaOH→NaCl+NH3↑+H2ONH_4Cl + NaOH → NaCl + NH_3↑ + H_2ONH4Cl+NaOH→NaCl+NH3↑+H2O
14. Why are food packets filled with nitrogen instead of oxygen?
Answer:
Oxygen causes food to spoil
due to oxidation and bacterial growth.
Nitrogen is used because:
It is an inert gas
– does not react with food.
Prevents the growth of bacteria
and fungi.
Keeps chips and snacks fresh
for a longer time.
Prevents rancidity
of oils and fats.
Maintains crispness
of packaged food.
15. Why does milk turn sour over time? What chemical change occurs?
Answer:
Milk
contains lactose (a type of sugar)
.
When left open,
lactic acid bacteria (Lactobacillus)
convert
lactose into lactic acid
.
Chemical reaction:
C12H22O11+H2O→4C3H6O3C
_{
12}H_{22}O_{11} + H_2O → 4C_3H_6O_3C12H22O11+H2O→4C3H6O3
Effects:
Increase in acidity
(Lower pH).
Coagulation of proteins
(Milk curdles).
Formation of curd
(Fermented milk).
Prevention:
Refrigeration
slows bacterial growth
.
Pasteurization
kills bacteria
.
16. What is the role of pH in agriculture?
Answer:
Soil pH affects plant growth
and nutrient absorption.
Optimal soil pH:
6-7.5
Acidic Soil (pH < 6):
Deficiency of
calcium and magnesium
.
Solution:
Add
slaked lime (
Ca(
OH)₂) or quicklime (
CaO
)
.
Alkaline Soil (pH > 7.5):
3. Poor absorption of
iron, zinc, phosphorus
.
4.
Solution:
Add
organic matter like manure or
sulphur
.
Farmers use pH meters
to test soil acidity and apply fertilizers accordingly.
17. Explain the effect of acid rain on monuments like the Taj Mahal.
Answer:
Acid rain contains sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
Reaction with Marble (
CaCO
₃):
CaCO3+H2SO4→CaSO4+CO2+H2OCaCO_3 + H_2SO_4 → CaSO_4 + CO_2 + H_2OCaCO3+H2SO4→CaSO4+CO2+H2O
Effects on Taj Mahal:
Marble
loses its shine
(Marble cancer).
Formation of
yellowish patches
.
Erosion of
carved designs
.
Weakens
structural strength
.
Prevention Measures:
5.
Restrict industrial pollution
near monuments.
6.
Use cleaner fuels
to reduce emissions.
7.
Regular cleaning and maintenance
of heritage sites.
18. How does acid rain affect aquatic life and soil?
Answer:
Acid rain contains sulfuric and nitric acid
from pollution.
Effects on Aquatic Life:
Lowers water pH
, making it toxic.
Kills fish and amphibians
.
Dissolves heavy metals
like lead into water.
Effects on Soil:
4. Reduces
fertility
by removing nutrients.
5. Kills
useful soil bacteria
.
6. Increases
soil erosion
.
19. Why does tamarind taste sour? Explain the chemical reason.
Answer:
Tamarind contains
tartaric acid
(C₄H₆O₆), which is responsible for its sour taste.
Acidic substances taste sour
due to
H⁺ ions
.
Other natural acids:
Citric acid
– Lemons, oranges.
Acetic acid
– Vinegar.
Lactic acid
– Curd.
20. Why do acids conduct electricity while solid salt does not?
Answer:
Acids release free H⁺ ions in aqueous solution
, allowing current flow.
Solid salt (NaCl) does not conduct electricity
because:
No free ions in solid form
.
When dissolved in water
, Na⁺ and Cl⁻ become free, making it conductive.
Example:
HCl in water
: Conducts electricity.
Glucose in water
: Does not conduct (No ions).
