Acids, Bases, Salts Class 8 Questions and Answers Notes Basic Science Chapter 13 Kerala Syllabus

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Class 8 Basic Science Chapter 13 Acids, Bases, Salts Question Answer Notes

Class 8 Basic Science Chapter 13 Notes Kerala Syllabus Acids, Bases, Salts Question Answer

Acids, Bases, Salts Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
Complete the table

Answer:

Substance	The colour change that occurs when exposed to moist red litmus	The colour change that occurs when exposed to moist blue litmus
Lemon juice	No Change	Turns Red
Lime water	Turns Blue	No Change
Sodium hydroxide	Turns Blue	No Change
Vinegar	No Change	Turns Red
Dilute hydrochloric acid	No Change	Turns Red

Question 2.
Find out which of the following statements is correct.
i. Nitrogen dioxide dissolves in water to form nitric acid.
ii. Phosphorus pentoxide (P₂O₅) is a nonmetal oxide.
iii. Sulphur trioxide turns moist red litmus blue.
Answer:
Statements (i) and (ii) are correct.

Question 3.
Explain any two cases where the importance of neutralisation reaction used in daily life.
Answer:
Neutralisation (Acid + Base → Salt + Water) is used to cancel out the effects of an acid with a base, or vice versa.

1. Treating Indigestion (Acidity): Our stomach produces hydrochloric acid HCl for digestion. If too much acid is produced, it causes acidity and discomfort. We take antacids (like Milk of Magnesia, Mg(OH)₂, which are basic medicines. The antacid (base) neutralizes the excess acid in the stomach, providing relief.

2. Controlling Soil pH: The pH of the soil is crucial for crop growth. If the soil is too acidic, farmers add a base (like slaked lime, Ca(OH)₂ to neutralize it. If the soil is too basic, farmers add an acidic substance (like ammonium sulphate) to neutralize it.

Question 4.
Solutions of some chemicals used in the laboratory are given in Box 1 below. Using these, write which salts given in Box 2 you can identify. Explain the method of experiment and observation.

Answer:
We can identify Ammonium carbonate and Ammonium chloride.
To identify Ammonium carbonate NH₄CO₃
Method: Take a sample of the salt solution. Add a few drops of Dilute HCl.
Observation: You will see bubbles (effervescence). If this gas is passed through lime water, it will turn milky.
Reason: Acids react with carbonates to produce carbon dioxide gas.
To identify Ammonium chloride (NH₄Cl): Method: Take a sample of the salt solution. Add a few drops of Silver nitrate solution.

Observation: A white precipitate (of Silver chloride, AgCl will form.
Reason: Silver nitrate is the test for the chloride ion Cl^–.

Question 5.
A bottle of salt in the lab had its label on it disintegrated. The details of the experiments conducted to identify the salt are given below.
• When a little barium chloride solution was added to the salt solution, a white precipitate formed.
• When dilute hydrochloric acid was added to the white precipitate, no observable change occurred.
Which salt is it? (Ammonium sulphate, Ammonium carbonate)
Answer:
Clues:
A white precipitate formed when Barium chloride BaCl₂ solution was added.
When dilute hydrochloric acid HCl was added to this precipitate, no observable change occurred.
Which salt is it? (Ammonium sulphate, Ammonium carbonate)

Reasoning:
Test 1 (Barium chloride): Both Ammonium sulphate NH₄SO₄ and Ammonium carbonate NH₄CO₃ would form a white precipitate with Barium chloride (BaCl₂).
NH₄SO₄ + BaCl₂ → BaSO₄ (white precipitate) + NH₄Cl
NH₄CO₃ + BaCl₂ → BaCO₃ (white precipitate) + NH₄Cl

Test 2 (Dilute HCl): This is the deciding test.
The precipitate did not change when HCl was added. This is a property of Barium sulphate BaSO₄.
If the precipitate had been Barium carbonate BaCO₃, it would have reacted with the HCl (acid + carbonate) and dissolved. Answer: The salt is Ammonium sulphate.

Question 6.
A colourless acid solution is in a bottle in the laboratory. 5 mL of it is taken in a test tube. 2 mL of dilute hydrochloric acid is added to it, no observable changes occur. After taking 5 ml. of the solution in another test tube, when 2 mL of silver nitrate solution is added, a white precipitate is formed.
i) Which acid is the solution in the bottle? When NaOH solution is added dropwise to 5 mL of the solution, it is observed that the pH gradually increases.
ii) When the pH reaches 7, what are the possible compounds present in the solution?
iii) Write the chemical equation for the reaction between NaOH and the acid solution.
Answer:
Test 1: Solution + dilute HCl → No observable change.
Test 2: Solution + Silver nitrate → A white precipitate is formed.
Test 3: When NaOH (base) is added, the pH gradually increases (this confirms the initial solution is an acid).
i) Test 2 (Silver nitrate) gives a white precipitate. This is the positive test for the Chloride ion Cl^–.
Since the solution is an acid and it contains Cl^– ions, the acid must be Hydrochloric acid (HCl).
(Test 1 confirms it’s not a carbonate solution, which we already know since it’s an acid).

ii) When pH = 7, the solution is neutral. This is the exact point of neutralisation.
The reaction is: HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water).
Answer:
The compounds present are Sodium chloride (NaCl) and Water (H₂O).

iii) Write the chemical equation for the reaction between NaOH and the acid solution.
Answer:
NaOH + HCl → NaCl + H₂O

Basic Science Class 8 Chapter 13 Question Answer Kerala Syllabus

Textbook Page No : 219 & 220

Question 1.
What taste do they have in common?
Answer:
They are all sour in taste.

Question 2.
What could be the reason?
Answer:
The sour taste is due to the presence of acids, which are substances that produce hydrogen ions (H⁺) in aqueous solution.

Question 3.
What colour changes occur when red litmus paper and blue litmus paper are used to test these food items?
Answer:
Acids turn blue litmus paper red. Red litmus paper will show no change.

Question 4.
Conduct an experiment to note the colour change to litmus paper with hydrochloric acid, sulphuric acid and nitric acid…
Answer:
Observation: All three strong acids will turn blue litmus paper red.

Question 5.
Reaction of Zinc with dilute Hydrochloric acid (Observation and Reason):
Answer:
Observation: A pop sound will be heard when a burning matchstick is brought near the test tube.
Reason: This observation confirms the production of hydrogen gas (H₂), which is liberated when highly reactive metals (like zinc and magnesium) react with acids.

Question 6.
Reaction with Carbonates (Observation when gas is passed through clear lime water):

Answer:
Observation: The clear lime water turns milky (or cloudy).

Question 7.
Complete the table given below (Table 13.1):

Answer:

Metal	Acid	Chemical equation
Zinc	Hydrochloric acid	Zn + 2HCl → ZnCl2 + H2
Zinc	Sulphuric acid	Zn + H2SO4 → ZnSO4 +H2
Magnesium	Hydrochloric acid	Mg + 2HCl → MgCl2 + H2
Magnesium	Sulphuric acid	Mg + H2SO2 → MgSO2 + H2

Textbook Page No : 221 & 222

Question 8.
Which gas is released through the delivery tube?
Answer:
Carbon dioxide gas (CO₂).

Question 9.
What is the symbol for hydrogen?
Answer:
H.

Question 10.
What is the chemical formula of hydrochloric acid?
Answer:
HCl.

Question 11.
Which are the ions formed when nitric acid dissolves in water?
Answer:
H⁺ (hydrogen ion) and NO₃^– (nitrateion).

Question 12.
Complete the table given below (Table 13.2):

Answer:

Name of acid	Chemical formula	Ions liberated when dissolved in water
Hydrochloric acid	HCl	H+, Cl–
Sulphuric acid	H2SO4	2H+, SO42-
Carbonic acid	H2CO3	2H+, CO32-
Phosphoric acid	H3PO4	3H+, PO43-

Question 13.
Which is the gas liberated when a soda bottle is opened?
Answer:
Carbon dioxide gas (CO₂).

Question 14.
Is soda water acidic or basic?
Answer:
Soda water is acidic.

Question 15.
Which is the acid in soda water?
Answer:
Carbonic acid.

Question 16.
Write the chemical formula of the acid in soda water.
Answer:
H₂CO₃.

Question 17.
Complete the chemical equation for the reaction of sulphur dioxide (SO₂) gas in water to form acid:
Answer:
SO₂ + H₂O → H₂SO₃ (sulphurous acid).

Textbook Page No : 223

Question 18.
Write the chemical formula and chemical name of the acids formed when the oxides given in the table react with water (Table 13.5):

Answer:

Main oxide of the element	Chemical formula of the acid formed by reacting with water	Chemical name of the acid formed by reacting with water
Nitrogen dioxide (NO2)	HNO3	Nitric acid
Phosphorus pentoxide (P2O5)	H3PO4	Phosphoric acid
Sulphur trioxide (SO3)	H2SO4	Sulphuric acid

Textbook Page No : 224 & 225

Question 19.
List the General properties of bases:
Answer:

1. Turns red litmus blue.
2. Has a bitter taste.
3. Feels soapy or slippery to the touch.

Question 20.
White powder obtained after burning magnesium ribbon:
Answer:
The white powder is Magnesium oxide (MgO).

Question 21.
Nature of the product when MgO is added to water:
Answer:
The product is Magnesium hydroxide (Mg(OH)₂). It is basic and will turn red litmus paper blue.

Question 22.
Complete the chemical equation of the reaction of quicklime (CaO) with water:
Answer:
CaO + H₂O → Ca(OH)₂ (Calcium hydroxide).

Question 23.
Are CaO and MgO, metal oxides or nonmetal oxides?
Answer:
They are metal oxides. (Metal oxides generally show basic properties).

Question 24.
Complete the ionisation equation for calcium hydroxide:
Answer:
Ca(OH)₂ → Ca²⁺ + 2OH^–

Question 25.
What is the common ion liberated when alkalies dissolve in water?
Answer:
The common ion is the hydroxide ion (OH^–).

Textbook Page No : 226 & 227

Question 26.
Which was the colour of NaOH solution when phenolphthalein was added?
Answer:
The solution turned pink or magenta.

Question 27.
What property of NaOH solution does this indicate?
Answer:
It indicates that the solution is basic.

Question 28.
Will NaOH remain in the conical flask when the colour completely disappears?
Answer:
No. The disappearance of color (endpoint) means the acid has neutralized the base, leaving mostly salt and water.

Question 29.
What is the pH value of a neutral solution?
Answer:
The pH value of a neutral solution is 7.

Question 30.
What characteristics do solutions with a pH value greater than 7 show?
Answer:
They are basic.

Question 31.
What characteristics do solutions with a pH value less than 7 show?
Answer:
They are acidic.

Textbook Page No : 228 & 229

Question 32.
Complete Table 13.7 (using typical nature):

Answer:

Name of substance	pH value (Typical)	Acidic/Basic/Neutral
Lemon juice	< 7	Acidic
Dilute Hydrochloric acid	< 7	Acidic
Water	≈ 7	Neutral
Common salt solution	≈ 7	Neutral
Sodium hydroxide solution	> 7	Basic
Soap solution	> 7	Basic

Question 33.
As the pH value increases, does it become more acidic or more basic?
Answer:
It becomes more basic.

Question 34.
What are the products formed when sodium hydroxide and dilute hydrochloric acid react?
Answer:
Sodium chloride (NaCl) (a salt) and water (H₂O).

Question 35.
What is the product formed when the common component of the acid (H⁺) and the common component of the alkali (OH^–) combine?
Answer:
Water (H₂O).

Question 36.
What is the product formed when the positive ion in sodium hydroxide (Na⁺) and the negative ion in hydrochloric acid (Cl^–) combine?
Answer:
The salt Sodium chloride (NaCl).

Question 37.
Complete the chemical equation for the reaction between dilute sulphuric acid and magnesium hydroxide solution:
Answer:
Mg(OH)₂ + H₂SO₄ → MgSO₄ + 2H₂O

Question 38.
What is the salt formed?
Answer:
Magnesium sulphate (MgSO₄).

Question 39.
Find and write the acid and alkali/base that must be reacted to obtain the salts:

Answer:

Salt	Chemical Formula	Acid	Alkali/Base
Calcium sulphate	CaSO4	H2SO4 (Sulphuric acid)	Ca(OH)2 (Calcium hydroxide)
Aluminium sulphate	Al2(SO4)3	H2SO4 (Sulphuric acid)	Al(OH)3 (Aluminium hydroxide)
Barium nitrate	Ba(NO3)2	HNO3 (Nitric acid)	Ba(OH)2 (Barium hydroxide)

Textbook Page No : 230

Question 40.
What are the products formed when sodium hydroxide and dilute nitric acid react?
Answer:
NaOH + HNO₃ → NaNO₃ + H₂O

Question 41.
What is the salt formed here?
Answer:
Sodium nitrate (NaNO₃).

Question 42.
Identifying Nitrate Salts (Brown Ring Test)
Answer:
The experiment involves mixing a nitrate salt solution (like Ammonium nitrate) with freshly prepared ferrous sulphate solution and then carefully adding concentrated sulphuric acid.
Observation: A distinct brown ring will form at the junction of the two liquid layers (the aqueous solution and the concentrated sulphuric acid).

Question 43.
Identifying Carbonate Salts
Answer:
The experiment involves reacting a carbonate salt solution (like Sodium carbonate) with an acid (Dilute Hydrochloric Acid) and passing the resultant gas through clear lime water.
Observation: The clear lime water will turn milky (or cloudy). This observation confirms that the gas released is carbon dioxide (CO₂), which is characteristic of the reaction between an acid and a carbonate salt.

Class 8 Basic Science Chapter 13 Question Answer Extended Activities

Question 1.
Collect soil from different parts around your house. Mix it with some water and stir it well. After some time, collect the clear water and find its pH value using pH solution, pH paper or pH meter. Similarly, find the pH of water from different sources and display it on a chart.

Question 2.
Collect information from farmers about the methods they use to increase or decrease the acidity of the soil while preparing the soil suitable for different crops in your area and prepare a report.

Acids, Bases, Salts Class 8 Notes

Class 8 Basic Science Acids, Bases, Salts Notes Kerala Syllabus
Acid

• Acids are substances that can increase the concentration of hydrogen ions (H⁺) in an aqueous solution (in
• water).
  Properties: Acids have a sour taste and turn blue litmus paper red.
• Common Component: The common component in all acids is Hydrogen (H). which is liberated as H+ ions (or hydronium ions, H₃O⁺) in water. These ions are the basis for all acidic properties.
• Acids have several key chemical properties that can be used to identify them.
  1. Taste: They have a sour taste. (Note: It is dangerous to taste chemicals in a lab).
  2. Litmus Test: Acids turn blue litmus paper red.
  3. Reaction with Reactive Metals: Acids react with highly reactive metals (like Zinc and Magnesium) to liberate Hydrogen gas (H₂).
  4. Reaction with Carbonates: Acids react with carbonates (like calcium carbonate/marble) to liberate Carbon Dioxide gas (CO₂).

ആസിഡുകൾക്ക് പ്രധാനമായും 4 സ്വഭാവങ്ങ ളുണ്ട്

• പുളി രുചി.
• നീല ലിറ്റ്മസിനെ ചുവപ്പ് ആക്കുന്നു.
• സിങ്ക് (Zinc), മഗ്നീഷ്യം (Magnesium) തുട ങ്ങിയ ക്രിയാശീലമുള്ള ലോഹങ്ങളുമായി പ വർത്തിച്ച് ഹൈഡ്രജൻ (H₂) വാതകം ഉണ്ടാ ക്കുന്നു.
• കാർബണേറ്റുകളുമായി (ഉദാഹരണത്തിന്, മാ ർബിൾ) പ്രവർത്തിച്ച് കാർബൺ ഡൈ ഓക് സൈഡ് (CO₂) വാതകം ഉണ്ടാക്കുന്നു.

Organic Acids: These are generally weaker acids found in food.

• Lemon: Citric acid
• Yoghurt/Curd: Lactic acid
• Tamarind: Tartaric acid
• Vinegar: Acetic acid

Mineral Acids : These are stronger acids typically prepared in a lab from minerals (e.g., Hydrochloric acid, Sulphuric acid).

Common Acids

Name of Acid	Chemical Formula	Used/Found In
Hydrochloric Acid	HCl	Gastric juice, industrial cleaning
Sulphuric Acid	H2SO4	Batteries, fertilizers, King of Chemicals
Carbonic Acid	H2CO3	Soda water, soft drinks
Acetic Acid	CH3COOH	Vinegar (food preservative)

Acid Reactions
1. With Reactive Metals: Acids react with metals like Zinc (Zn) and Magnesium (Mg) to liberate Hydrogen gas (H₂).
Mg + HCl → MgCl₂ + H₂

2. With Carbonates: Acids react with car-bonates (like marble, CaCO₃) to liberate Carbon Dioxide gas (CO₂).
Test for CO₂: It turns clear lime water milky.

3. With Non-metal Oxides: Non-metal oxides (like CO₂, SO₂) dissolve in water to form acids.
CO₂ + H₂O → H₂CO₃ (Carbonic acid)

Substance Acidic

• The general properties of all acids (like sour taste, turning blue litmus red, and reacting with metals) are because of a common component.
• The Common Component: Hydrogen (H) is the common component in all acids.
• Acids are substances that can increase the concentration of hydrogen ions (H⁺) in an aqueous solution (in water).
• Hydronium Ions (H₃O⁺): These liberated H⁺ ions are highly reactive and combine with water (H₂O) molecules to form hydronium ions (H₃O⁺).
  H⁺ + H₂O → H₃O⁺

എല്ലാ ആസിഡുകളിലും പൊതുവായി അടങ്ങിയി രിക്കുന്ന ഘടകമാണ് ഹൈഡ്രജൻ (H). ആസിഡു കൾ ജലത്തിൽ ലയിക്കുമ്പോൾ (aqueous solu tion) ഹൈഡ്രജൻ അയോണുകൾ (H⁺) സ്വതന്ത്ര മാക്കുന്നു. ഈ H⁺ അയോണുകളാണ് ആസിഡു കളുടെ എല്ലാ പൊതു സ്വഭാവങ്ങൾക്കും കാരണം.

Acids from Non-metal Oxides
A major category of acids is formed when non-metal oxides (oxides of elements like Carbon, Sulphur, Nitrogen) react with water.

• General Rule: The substances formed when nonmetal oxides react with water generally show acidic properties.
• Formula: Non-metal Oxide + Water → Acid

അലോഹ ഓക്സൈഡുകൾ (Non-metal oxides) ജലവുമായി (Water) പ്രവർത്തിക്കുമ്പോൾ ആസിഡുകൾ ഉണ്ടാകുന്നു. അതുകൊണ്ട് അലോ ഹ ഓക്സൈഡുകളെ ‘ആസിഡ് അൻഹൈ ഡ ഡുകൾ’ എന്നും വിളിക്കാറുണ്ട്.

Examples:
1. Soda Water:

• The gas liberated when a soda bottle is opened is Carbon dioxide (CO₂).
• This CO₂ (a nonmetal oxide) reacts with water (H₂O) to form Carbonic acid (H₂CO₃), which makes soda water acidic.
• CO₂ + H₂O → H₂CO₃ (Carbonic acid)

2. Sulphur Dioxide:
• SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

Acid Rain
Acid rain refers to any precipitation (rain, snow, fog, etc.) that has a pH below 5.6, making it significantly more acidic than normal rainwater.

Formation
Acid rain is primarily caused by two major air pollutants released from human activities, mainly the burning of fossil fuels (coal and petroleum) in industries and vehicles:

1. Sulphur Dioxide (SO₂): Released mainly from power plants. This gas dissolves in atmospheric water to form Sulphuric Acid (H₂SO₄).
2. Nitrogen Oxides (NO₂): Released mainly from vehicles. These gases dissolve in atmospheric water to form Nitric Acid (HNO₃).

These strong mineral acids then fall to the Earth as acid rain.

Effects
Acid rain has severe detrimental effects:

• Corrosion: It accelerates the corrosion of metal structures and the deterioration of stone buildings and monuments (like marble, which is calcium carbonate), leading to “stone cancer.”
• Aquatic Life: It lowers the pH of lakes and rivers, making the water toxic and threatening the survival of fish and other aquatic organisms.
• Vegetation/Soil: It damages leaves and increases the acidity of the soil, leaching essential nutrients and hindering the growth of crops and forests.

Bases (ബേസുകൾ)
Just as we studied acids, let’s look at the properties of bases.

General properties of bases:

• They have a bitter taste and feel soapy to the touch.
• Bases turn red litmus paper blue.
• Source: Metal oxides (ലോഹ ഓക്സൈഡുകൾ) (e.g., Magnesium oxide MgO, Calcium oxide CaO) generally show basic properties.
• Metal Oxide + Water → Base
  MgO + H₂O → Mg(OH)₂ (Magnesium hydroxide)

ആസിഡുകൾ അലോഹ ഓക്സൈഡുകൾ (nonmetal oxides) ജലത്തിൽ ലയിക്കുമ്പോൾ ഉണ്ടാ കുന്നതുപോലെ, ലോഹ ഓക്സൈഡുകൾ (metal oxides) ജലത്തിൽ ലയിക്കുമ്പോഴാണ് ബേസു കൾ ഉണ്ടാകുന്നത്. ഉദാഹരണത്തിന്, മഗ്നീഷ്യം ഓക്സൈഡ് അല്ലെങ്കിൽ കാൽസ്യം ഓക്സൈഡ്.

Alkalis

• Alkalis are bases that dissolve in water. (Not all bases dissolve in water).
• (Chemical): Alkalis are substances that can increase the concentration of hydroxide ions (OH^–) in an aqueous solution.
• The hydroxide ion (OH^–) is the common ion liberated by all alkalis when dissolved in water. This ion is responsible for all the general properties of bases.

Dissociation of Alkalis:
NaOH → Na⁺ + OH^– (hydroxide ion)
Ca(OH)² → Ca²⁺ + 2OH^–
ആസിഡുകളുടെ പൊതുസ്വഭാവത്തിന് കാരണം H⁺ അയോണുകൾ ആയതുപോലെ, ബേസുകളുടെ പൊതുസ്വഭാവത്തിന് കാരണം ഹൈഡ്രോക്സൈ ഡ് അയോണുകൾ (OH^–) ആണ്. ജലത്തിൽ ലയി ക്കുമ്പോൾ OH^– അയോണുകൾ സ്വതന്ത്രമാക്കാൻ കഴിയുന്ന ബേസുകളെയാണ് ക്ഷാരങ്ങൾ (Alkalis) എന്ന് വിളിക്കുന്നത്.

Common name	Chemical name	Chemical formula
Caustic soda	Sodium hydroxide	NaOH
Milk of lime	Calcium hydroxide	Ca(OH)2
Caustic potash	Potassium hydroxide	KOH

Neutralisation Reaction
The chemical reaction in which an acid and a base react and lose their properties to form water and a salt is known as neutralisation reaction. The common H⁺ ions from the acid and OH^– ions from the base combine to form H₂O.
Acid + Base → Salt + Water

• Example: NaOH + HCl → NaCl +H₂O
  (Sodium Hydroxide + Hydrochloric Acid → Sodium Chloride + Water)
• Indicator Use: Phenolphthalein is an indicator used in neutralisation. It is pink in a basic solution and turns colourless when the solution becomes neutral or acidic.
• Example (Antacid): Taking a basic antacid (like Mg(OH)₂, Milk of Magnesia) to neutralize excess stomach acid (HCl).
• Example (Soil): Adding slaked lime (base) to reduce soil acidity.

ആസിഡും ബേസും തമ്മിൽ പ്രവർത്തിച്ച് അവ യുടെ ഗുണങ്ങൾ പരസ്പരം ഇല്ലാതാവുകയും, തത്ഫലമായി ലവണവും (Salt) ജലവും (Water) ഉണ്ടാകുകയും ചെയ്യുന്ന പ്രവർത്തനമാണ് നിർവീ രീകരണം (Neturalisation).

pH Value

• To measure the “degree” of acidic or basic nature of a substance, we use the pH scale.
• The pH scale is used to determine the degree of acidic or basic nature of a substance. It was developed by the Danish scientist Sorensen and is based on the concentration of H⁺ ions in the solution.

• The Scale (Fig 13.4): The scale ranges from 1 to 14.
  • pH value less than 7 (< 7): The solution is Acidic (ആസിഡ് സ്വഭാവം).
  • pH value of 7: The solution is Neutral (നിർവീരും).
  • pH value greater than 7 (> 7): The solution is Basic (ബേസിക് സ്വഭാവം).
• Measurement: We can measure pH using pH paper, pH solution, or a pH meter.
• Trend: As the pH value increases, the substance becomes more basic (and less acidic).

ഒരു പദാർത്ഥം ആസിഡ് ആണോ ബേസ് ആണോ എന്നും, അതിന്റെ ശക്തി എത്രത്തോളമുണ്ടെന്നും അളക്കാനുള്ള ഒരു സ്കെയിൽ ആണ് pH കയിൽ. ഇത് 1 മുതൽ 14 വരെയാണ്.

Application: pH in Soil (മണ്ണിലെ pH)
The pH of the soil is a critical factor for the proper growth of crops.

• To reduce acidity (if soil is too acidic):
  A base like slaked lime (Calcium hydroxide) is added.
• To reduce basicity (if soil is too basic):
  An acidic substance like ammonium sulphate or aluminium sulphate is added.

Salts

• Salts are ionic compounds formed by the reaction of an acid and a base (neutralisation reaction).
• Formation:
  1. The common component of the acid (H⁺) and the common component of the base (OH^–) combine to form Water (H₂O).
  2. The positive ion from the base (e.g., Na+ from NaOH) combines with the negative ion from the acid (e.g., Cl^– from HCl) to form the Salt.

ഒരു ആസിഡും ബേസും തമ്മിൽ പ്രവർത്തിക്കു മ്പോൾ (neturalisation), ആസിഡിലെ H⁺ അയോ ണും ബേസിലെ OH^– അയോണും ചേർന്ന് ജലം (Water) ഉണ്ടാകുന്നു. ബാക്കിയുള്ള, ബേസിലെ പോസിറ്റീവ് അയോണും ആസിഡിലെ നെഗറ്റീവ് അയോണും ചേർന്ന് ഉണ്ടാകുന്ന പദാർത്ഥമാണ് ലവണം (Salt).

Examples of Salt Formation:

• HCl (acid) + NaOH (base) → NaCl(salt) + H₂O (water)
• H₂SO₄ (acid) + Mg(OH)₂ (base) → MgSO₄ (salt) + H₂O (water)
• HNO₃ (acid) + NaOH (base) → NaNO₃(salt) + H₂O(water)

Identification of Ions in Salts (അയോണുകളെ തിരിച്ചറിയൽ)
We can use chemical tests to identify the negative ions present in a salt.

• Test for Chloride (Cl^–) ion:
  Reagent: Add Silver Nitrate (AgNO₃) solution.
  Observation: A white precipitate (വെളുത്ത അവക്ഷിപ്തം)) of Silver Chloride (AgCl) is formed.
• Test for Sulphate (SO₄^2-) ion:
  Reagent: Add Barium Chloride (BaCl₂) solution.
  Observation: A white precipitate of Barium Sulphate (BaSO₄) is formed. Confirmation: This precipitate does not dissolve when dilute HCl is added to it.
• Test for Nitrate (NO₃^–) ion (Brown Ring Test):
  Reagent: Add freshly prepared Ferrous Sulphate (FeSO₄) solution, and then add concentrated Sulphuric Acid (H₂SO₄) slowly down the sides of the test tube.
  Observation: A brown ring forms at the junction where the two liquids meet.